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Solar Arrays

Spacewalking astronautsunfold one of Hubble's newhighly efficient solar arraysthat will provide 20 percentmore power to the orbitingobservatory.

Power Control Unit

SM3B astronautinstalls replacementfor Telescope's agingPower Control Unit.

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Hubble Space TelescopeServicing Mission 3BMedia Reference Guide

Prepared by Lockheed Martin forthe National Aeronautics and Space Administration

Special thanks to everyone whohelped pull this book together.

Buddy Nelson – Chief writer/editorMel Higashi – Design and layoutPat Sharp – Text and graphics integration

Computer generated 3-D illustrations provided byTim Cole, Kevin Balch, David Green, Nick Dellwo

Background information provided byBrian Woodworth, Donna Weaver, Ann Jenkins,Monty Boyd, Ray Villard, Dave Leckrone

Who Was Edwin P. Hubble?

ne of the great pioneers of modern astronomy,the American astronomer Edwin Powell Hubble

(1889–1953), started out by getting a law degreeand serving in World War I. However, after prac-ticing law for one year, he decided to “chuck law forastronomy and I knew that, even if I were secondrate or third rate, it was astronomy that mattered.”

He completed a Ph.D. thesis on the PhotographicInvestigation of Faint Nebulae at the University ofChicago and then continued his work at MountWilson Observatory, studying the faint patches ofluminous “fog” or nebulae in the night sky.

Using the largest telescope of its day, a 2.5-mreflector, he studied Andromeda and a number ofother nebulae and proved that they were other starsystems (galaxies) similar to our own Milky Way.

He devised the classification scheme for galaxiesthat is still in use today, and obtained extensiveevidence that the laws of physics outside the Galaxy are the same as on Earth—in his own words:“verifying the principle of the uniformity of nature.”

In 1929, Hubble analyzed the speeds of recessionof a number of galaxies and showed that the speedat which a galaxy moves away from us is propor-tional to its distance (Hubble’s Law). Thisdiscovery of the expanding universe marked thebirth of the “Big Bang Theory” and is one of thegreatest triumphs of 20th-century astronomy.

In fact, Hubble’s remarkable discovery could havebeen predicted some 10 years earlier by none otherthan Albert Einstein. In 1917, Einstein applied hisnewly developed General Theory of Relativity tothe problem of the universe as a whole. Einsteinwas very disturbed to discover that his theorypredicted that the universe could not be static, buthad to either expand or contract. Einstein foundthis prediction so unbelievable that he went backand modified his original theory in order to avoidthis problem. Upon learning of Hubble’s discov-eries, Einstein later referred to this as “the biggestblunder of my life.”

— ESA Bulletin 58

Edwin Hubble (1889–1953) at the 48-inchSchmidt telescope on Palomar Mountain

O

Photo courtesy of the Carnegie Institution of Washington

INTRODUCTION 1-1Hubble Space Telescope Configuration 1-2

Optical Telescope Assembly 1-2Science Instruments 1-4Support Systems Module 1-6Solar Arrays 1-6Computers 1-6

The Hubble Space Telescope Program 1-6The Value of Servicing 1-7

HST SERVICING MISSION 3B 2-1Reasons for Orbital Servicing 2-1Orbital Replacement Units 2-1Shuttle Support Equipment 2-4

Remote Manipulator System 2-4Space Support Equipment 2-4Flight Support System 2-5Rigid Array Carrier 2-5Second Axial Carrier 2-5Multi-Use Lightweight Equipment Carrier 2-6

Astronaut Roles and Training 2-6Extravehicular Crew Aids and Tools 2-7

Astronauts of Servicing Mission 3B 2-8Servicing Mission Activities 2-10

Rendezvous With Hubble 2-10Extravehicular Servicing Activities—Day by Day 2-11

Future Servicing Plans 2-18

HST SCIENCE AND DISCOVERIES 3-1Evolution of Stars and Planets 3-2

Elusive Planets 3-2Stars Under Construction 3-4Most Luminous Star 3-5

Earth’s Solar System 3-6Death of a Comet 3-6Crash on Jupiter 3-7Mars Close-up 3-7Dances of Light 3-8

Galaxies and Cosmology 3-9“Dark Energy” 3-9Black Holes 3-9Starburst Galaxies 3-9Stellar Kindergartens 3-10The Evolving Universe 3-10

Summary 3-11

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CONTENTS

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SCIENCE INSTRUMENTS 4-1Advanced Camera for Surveys 4-1

Physical Description 4-3ACS Optical Design 4-3Filter Wheels 4-4

Observations 4-4Near Infrared Camera and Multi-Object Spectrometer 4-4

Instrument Description 4-5NICMOS Specifications 4-6Observations 4-7

Space Telescope Imaging Spectrograph 4-7Physical Description 4-7STIS Specifications 4-10Observations 4-10

Wide Field and Planetary Camera 2 4-11Physical Description 4-11WFPC2 Specifications 4-13Observations 4-14

Astrometry (Fine Guidance Sensors) 4-14Fine Guidance Sensor Specifications 4-14Operational Modes for Astrometry 4-14Fine Guidance Sensor Filter Wheel 4-15Astrometric Observations 4-15

HST SYSTEMS 5-1Support Systems Module 5-2

Structures and Mechanisms Subsystem 5-3Instrumentation and Communications Subsystem 5-6Data Management Subsystem 5-7Pointing Control Subsystem 5-9Electrical Power Subsystem 5-11Thermal Control 5-12Safing (Contingency) System 5-13

Optical Telescope Assembly 5-14Primary Mirror Assembly and Spherical Aberration 5-15Secondary Mirror Assembly 5-18Focal Plane Structure Assembly 5-19OTA Equipment Section 5-19

Fine Guidance Sensor 5-20FGS Composition and Function 5-20Articulated Mirror System 5-21

Solar Arrays 5-21Science Instrument Control and Data Handling Unit 5-22

Components 5-22Operation 5-23

Space Support Equipment 5-24Orbital Replacement Unit Carrier 5-25Crew Aids 5-25

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HST OPERATIONS 6-1Space Telescope Science Institute 6-1

Scientific Goals 6-2STScI Software 6-2Selecting Observation Proposals 6-2Scheduling Telescope Observations 6-2Data Analysis and Storage 6-2

Space Telescope Operations Control Center 6-2Operational Characteristics 6-3

Orbital Characteristics 6-3Celestial Viewing 6-3Solar System Object Viewing 6-3Natural Radiation 6-4Maneuvering Characteristics 6-4Communications Characteristics 6-5

Acquisition and Observation 6-6

VALUE ADDED: The Benefits of Servicing Hubble 7-1Cost-Effective Modular Design 7-1

Processor 7-2Data Archiving Rate 7-3Detector Technology 7-3Cryogenic Cooler 7-3Solar Arrays 7-4Simultaneous Science 7-4

GLOSSARY 8-1

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ILLUSTRATIONS

1-1 The Hubble Space Telescope (HST)—shown in a clean room at Lockheed Martin 1-3Space Systems Company – Missiles & Space in Sunnyvale, California, beforeshipment to Kennedy Space Center—is equipped with science instrumentsand engineering subsystems designed as Orbital Replacement Units.

1-2 HST overall configuration 1-41-3 HST exploded view 1-51-4 HST specifications 1-61-5 Organization summary for HST program operational phase 1-72-1 Hubble Space Telescope Servicing Mission 3B Orbital Replacement Units 2-32-2 Servicing Mission 3B Payload Bay configuration 2-42-3 Flight Support System configuration—aft view 2-52-4 Rigid Array Carrier configuration 2-52-5 Second Axial Carrier configuration 2-62-6 Multi-Use Lightweight Equipment Carrier configuration 2-62-7 Neutral Buoyancy Laboratory at Johnson Space Center 2-72-8 The STS-109 mission has seven crewmembers: (clockwise from top) Commander 2-9

Scott D. Altman, Pilot Duane G. "Digger" Carey, Mission Specialist Nancy Jane Currie, Mission Specialist John M. Grunsfeld, Mission Specialist Richard M. Linnehan, Mission Specialist James H. Newman and Mission Specialist Michael J. Massimino.

2-9 Detailed schedule of extravehicular activities during SM3B 2-112-10 Deployment of new rigid solar array 2-142-11 Change-out of Power Control Unit 2-152-12 Installation of the Advanced Camera for Surveys 2-162-13 Installation of NICMOS cooling system radiator 2-172-14 Redeploying the Hubble Space Telescope 2-173-1 A vast “city” of stars in 47 Tucanae 3-2 3-2 Planetary nurseries under fire in Orion 3-33-3 Vast star-forming region in 30 Doradus Nebula 3-43-4 A brilliant star at the Milky Way’s core 3-53-5 Hubble discovers missing pieces of Comet LINEAR 3-63-6 Mars at opposition in 2001 3-73-7 Auroral storms on Jupiter 3-83-8 Galaxy NGC 3310 ablaze with active star formation 3-103-9 Spiral galaxy NGC 4013 viewed edge-on 3-104-1 Advanced Camera for Surveys (ACS) configuration 4-24-2 ACS Wide Field Channel optical design 4-34-3 ACS High Resolution/Solar Blind Channels optical design 4-34-4 ACS CCD filters 4-44-5 SBC filters 4-44-6 NICMOS Cooling System (NCS) 4-54-7 Near Infrared Camera and Multi-Object Spectrometer (NICMOS) 4-54-8 NICMOS optical characteristics 4-64-9 NICMOS specifications 4-7

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4-10 Space Telescope Imaging Spectrograph 4-74-11 STIS components and detectors 4-84-12 Simplified MAMA system 4-94-13 STIS specifications 4-104-14 Wide Field and Planetary Camera (WFPC) overall configuration 4-124-15 WFPC optics design 4-134-16 WFPC2 specifications 4-134-17 Fine Guidance Sensor (FGS) 4-144-18 FGS specifications 4-145-1 Hubble Space Telescope—exploded view 5-25-2 Hubble Space Telescope axes 5-25-3 Design features of Support Systems Module 5-35-4 Structural components of Support Systems Module 5-35-5 Aperture door and light shield 5-45-6 Support Systems Module forward shell 5-45-7 Support Systems Module Equipment Section bays and contents 5-55-8 Support Systems Module aft shroud and bulkhead 5-65-9 High Gain Antenna 5-65-10 Data Management Subsystem functional block diagram 5-75-11 Advanced computer 5-85-12 Data Management Unit configuration 5-85-13 Location of Pointing Control Subsystem equipment 5-105-14 Reaction Wheel Assembly 5-115-15 Electrical Power Subsystem functional block diagram 5-125-16 Placement of thermal protection on Support Systems Module 5-135-17 Light path for the main Telescope 5-155-18 Instrument/sensor field of view after SM3B 5-165-19 Optical Telescope Assembly components 5-165-20 Primary mirror assembly 5-175-21 Primary mirror construction 5-175-22 Main ring and reaction plate 5-175-23 Secondary mirror assembly 5-185-24 Focal plane structure 5-195-25 Optical Telescope Assembly Equipment Section 5-195-26 Cutaway view of Fine Guidance Sensor 5-205-27 Optical path of Fine Guidance Sensor 5-215-28 Solar Array wing detail comparison 5-225-29 Science Instrument Control and Data Handling unit 5-235-30 Command flow for Science Instrument Control and Data Handling unit 5-245-31 Flow of science data in the Hubble Space Telescope 5-25

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6-1 “Continuous-zone” celestial viewing 6-46-2 HST single-axis maneuvers 6-46-3 Sun-avoidance maneuver 6-56-4 TDRS-HST contact zones 6-57-1 Advanced scientific instruments installed (or to be installed) on HST pave the 7-1

way to new discoveries.7-2 Systems maintained and upgraded during each servicing mission 7-27-3 Processor improvements 7-27-4 Data archiving rate improvements 7-37-5 Increase in onboard pixels 7-37-6 Increase in HST infrared capability 7-37-7 Productivity gains with new solar arrays 7-47-8 Simultaneous use science instruments 7-4

hroughout history, humankind hasexpanded its knowledge of the universe by

studying the stars. Great scientists such asNicholaus Copernicus, Galileo Galilei, JohannesKepler, Issac Newton, Edwin Hubble andAlbert Einstein contributed significantly to ourunderstanding of the universe.

The launch of the Hubble Space Telescope in1990 signified another great step toward unraveling the mysteries of space. Spectaculardiscoveries such as massive black holes at thecenter of galaxies, the existence of precursorplanetary systems like our own, and the quan-tity and distribution of cold dark matter arejust a few examples of the Telescope’s findings.

With NASA’s Servicing Mission 3B, wecontinue to carry the quest for knowledge inthe 21st century.

Another Step in Our Journey to the Stars

T

About the Inside Covers

Three-dimensional computer models illustrate tasks that theSTS-109 crew will perform in orbit during Servicing Mission 3B.The models enable engineers to study task feasibility and toconfirm that astronauts can safely reach and service componentsand locations on the spacecraft. These dimensionally accurate,visually correct images help the extravehicular activity servicingteam prepare to install new components and upgrade functionalsystems on the Telescope.

1-1

azing through his firstcrude telescope in the 17thcentury, Galileo discovered

the craters of the Moon, thesatellites of Jupiter and the ringsof Saturn. These observations ledthe way to today’s quest for in-depth knowledge and under-standing of the cosmos. And fornearly 12 years NASA’s HubbleSpace Telescope (HST) hascontinued this historic quest.

Since its launch in April 1990,Hubble has provided scientificdata and images of unprecedentedresolution from which many newand exciting discoveries have beenmade. Even when reduced to raw

numbers, the accomplishments ofthe 12.5-ton orbiting observatoryare impressive:

• Hubble has taken about420,000 exposures.

• Hubble has observed nearly17,000 astronomical targets.

• Astronomers using Hubble datahave published over 3,200scientific papers.

• Circling Earth every 90minutes, Hubble has traveledabout 1.7 billion miles.

This unique observatory operatesaround the clock above theEarth’s atmosphere gatheringinformation for teams of scien-

tists who study the origin, evolu-tion and contents of the universe.The Telescope is an invaluabletool for examining planets, stars,star-forming regions of the MilkyWay, distant galaxies and quasars,and the tenuous hydrogen gaslying between the galaxies.

The HST can produce images ofthe outer planets in our solarsystem that approach the clarity ofthose from planetary flybys.Astronomers have resolved previ-ously unsuspected details ofnumerous star-forming regions ofthe Orion Nebula in the Milky Wayand have detected expanding gasshells blown off by exploding stars.

INTRODUCTION

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INTRODUCTION

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Using the Telescope’s high-resolution and light-gatheringpower, scientists have calibratedthe distances to remote galaxiesto precisely measure the expan-sion of the universe and therebycalculate its age. They havedetected and measured the rota-tion of dust, gas and stars trappedin the gravitational field at thecores of galaxies that portend thepresence of massive black holes.

Hubble’s deepest views of theuniverse, unveiling a sea ofgalaxies stretching back nearly tothe beginning of time, haveforced scientists to rethink someof their earlier theories aboutgalactic evolution. (Section 3 ofthis guide contains additionalinformation on the Telescope’sscientific discoveries.)

The Telescope’s mission is to spend20 years probing the farthest andfaintest reaches of the cosmos.Crucial to fulfilling this objective isa series of on-orbit manned serv-icing missions. During thesemissions astronauts performplanned repairs and maintenanceactivities to restore and upgrade theobservatory’s capabilities. To facili-tate this process, the Telescope’sdesigners configured science instru-ments and several vital engineeringsubsystems as Orbital ReplacementUnits (ORU)—modular packageswith standardized fittings acces-sible to astronauts in pressurizedsuits (see Fig. 1-1).

The First Servicing Mission (SM1)took place in December 1993 andthe Second Servicing Mission(SM2) in February 1997. Hubble’sThird Servicing Mission was sepa-rated into two parts: ServicingMission 3A (SM3A) flew inDecember 1999 and ServicingMission 3B (SM3B) is scheduledfor an early 2002 launch.

SM3B astronauts will:• Install a new science instru-

ment, the Advanced Camerafor Surveys (ACS).

• Fit Hubble with a new pair ofrigid solar arrays.

• Replace the Power Control Unit(PCU).

• Replace a Reaction WheelAssembly (RWA).

• Retrofit the Near InfraredCamera and Multi-ObjectSpectrometer (NICMOS).

• Install New Outer BlanketLayer (NOBL) insulation panels.

The ACS consists of three elec-tronic channels and a complementof filters and dispersers thatdetect light from the ultravioletto the near infrared (1200 to10,000 angstroms). This camerawill be able to survey a field with2.3 times the area of the WideField and Planetary Camera 2(WFPC2) currently on Hubble. Itwill provide four times as muchspatial information and up to fivetimes the sensitivity of WFPC2.The ACS will not replace WFPC2,however. WFPC2 will continuewith its spectacular observationson the Telescope.

Designed and built by GoddardSpace Flight Center (GSFC), theEuropean Space Agency (ESA)and Lockheed Martin SpaceSystems Company, the new solararrays will produce 20 percentmore power than the currentarrays. In addition, they are lesssusceptible to damage and theextreme temperature swingsinduced by Hubble’s orbit.

The PCU controls and distributeselectricity from the solar arraysand batteries to other parts of theTelescope. Although it is stillfunctioning, this PCU has beenon the Telescope since 1990 andsome of its relays have failed.Replacement will ensure properoperation over the long term.

One of four RWAs will be replaced.The reaction wheels are part of anactuator system that moves thespacecraft into commanded posi-tions. Using spin momentum, thewheels move HST into positionand then keep the spacecraftstable. The wheel axes areoriented so that Hubble canoperate with only three wheels.

The NICMOS, a dormant instru-ment, will be retrofitted with anew, experimental NICMOSCooling System (NCS) to returnit to active duty.

If time permits, NOBL insulationpanels will be installed to preventdamage to Hubble from sunlightand extreme temperature changesand to maintain the Telescope’snormal operating temperature.

Hubble Space TelescopeConfiguration

Figures 1-2 and 1-3 show theoverall Telescope configuration.Figure 1-4 lists specifications forthe Telescope. The majorelements are:• Optical Telescope Assembly

(OTA)—two mirrors and asso-ciated structures that collectlight from celestial objects

• Science instruments—devicesused to analyze the imagesproduced by the OTA

• Support Systems Module(SSM)—spacecraft structurethat encloses the OTA andscience instruments

• Solar Arrays (SA).

Optical Telescope Assembly

The OTA consists of twomirrors, support trusses and thefocal plane structure. The opticalsystem is a Ritchey-Chretiendesign, in which two specialaspheric mirrors form focusedimages over the largest possiblefield of view. Incoming lighttravels down a tubular baffle thatabsorbs stray light. The concaveprimary mirror—94.5 in. (2.4 m)in diameter—collects the lightand converges it toward theconvex secondary mirror, whichis only 12.2 in. (0.3 m) in diam-eter. The secondary mirror directsthe still-converging light backtoward the primary mirror andthrough a 24-in. hole in its centerinto the Focal Plane Structure,where the science instrumentsare located.

INTRODUCTION

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Fig. 1-1The Hubble Space Telescope (HST)—shown in a clean room at Lockheed MartinSpace Systems Company – Missiles & Space Operations in Sunnyvale, California,before shipment to Kennedy Space Center—is equipped with science instrumentsand engineering subsystems designed as Orbital Replacement Units.

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INTRODUCTION

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Science Instruments

Hubble can accommodate eight science instruments.Four are aligned with the Telescope’s main opticalaxis and are mounted immediately behind theprimary mirror. These axial science instruments are:• Space Telescope Imaging Spectrograph (STIS)• Faint Object Camera (FOC)• Near Infrared Camera and Multi-Object

Spectrometer (NICMOS)• Corrective Optics Space Telescope Axial

Replacement (COSTAR).

In addition to the four axial instruments, four otherinstruments are mounted radially (perpendicular to themain optical axis). These radial science instruments are:• Wide Field and Planetary Camera 2 (WFPC2)• Three Fine Guidance Sensors (FGS).

Space Telescope Imaging Spectrograph. STIS separates incoming light into its component wave-lengths, revealing information about the atomiccomposition of the light source. It can detect abroader range of wavelengths than is possible fromEarth because there is no atmosphere to absorb

certain wavelengths. Scientists can determine thechemical composition, temperature, pressure andturbulence of the target producing the light—all fromspectral data.

Faint Object Camera. The FOC was decommissionedin 1997 to better allocate existing resources. However,the camera remains turned on and available to scien-tists if needed. The FOC will be returned to Earthafter the ACS is installed in its place during SM3B.

Near Infrared Camera and Multi-ObjectSpectrometer. Use of this now-dormant instrumentwill resume after successful installation of NCSduring SM3B.

Corrective Optics Space Telescope AxialReplacement. COSTAR was installed on HST in 1993to fix a flaw in the shape of the primary mirror (acommon mirror fabrication defect called spherical aber-ration) that was detected shortly after Hubble’s launchin 1990. Because all the instruments now on theTelescope are equipped with corrective optics, COSTARno longer is needed, but it will remain on the Telescopeuntil its slot is filled by a new science instrument on SM4.

Fig. 1-2 HST overall configuration

Forward Shell

Primary Mirror

Aft Shroud

COSTAR andScienceInstruments

Axial (4)

Radial (1)

Solar Array (2)Fine Guidance Sensor (3)

Light Shield

Aperture DoorSecondaryMirror (2)

High Gain Antenna (2)

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INTRODUCTION

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Wide Field and Planetary Camera 2. WFPC2 is anelectronic camera that records images at two magnifi-cations. A team at the Jet Propulsion Laboratory (JPL)

in Pasadena, California,built the first WFPC anddeveloped the WFPC2.The team incorporated anoptical correction byrefiguring relay mirrors inthe optical train of thecameras. Each relay mirroris polished to a prescrip-tion that compensates forthe incorrect figure onHST’s primary mirror.Small actuators fine-tunethe positioning of thesemirrors on orbit.

Fine Guidance Sensors.The three FGSs have twofunctions: (1) providedata to the spacecraft’spointing system to keepHST pointed accurately ata target when one ormore of the science

instruments is being used to take data and (2) act as ascience instrument. When functioning as a scienceinstrument, two of the sensors lock onto guide stars

Fig. 1-3 HST exploded view

Hubble Space Telescope (HST)

WeightLength

DiameterOptical systemFocal lengthPrimary mirrorSecondary mirrorField of viewPointing accuracyMagnitude rangeWavelength rangeAngular resolutionOrbitOrbit timeMission

24,500 lb (11,110 kg)43.5 ft (15.9 m)10 ft (3.1 m) Light Shield and Forward Shell14 ft (4.2 m) Equipment Section and Aft ShroudRitchey-Chretien design Cassegrain telescope189 ft (56.7 m) folded to 21 ft (6.3 m)94.5 in. (2.4 m) in diameter12.2 in. (0.3 m) in diameterSee instruments/sensors0.007 arcsec for 24 hours5 mv to 30 mv (visual magnitude)1100 to 24,000 Å0.1 arcsec at 6328 Å320 nmi (593 km), inclined 28.5 degrees from equator97 minutes per orbit20 years

Fig. 1-4 HST specifications

Magnetic Torquer (4)


Support Systems Module Forward Shell

Optical Telescope AssemblySecondary Mirror Assembly

Secondary Mirror Baffle

Central Baffle

Optical Telescope AssemblyPrimary Mirror and Main Ring

Fine Guidance Optical Control Sensor (3)

Optical TelescopeAssembly FocalPlane Structure

SupportSystemsModule Aft Shroud

Fixed HeadStar Tracker (3)and Rate GyroAssembly

Radial ScienceInstrument Module (1)

Optical Telescope AssemblyEquipment Section

Optical Telescope AssemblyMetering Truss

Main Baffle

Light Shield

ApertureDoor

Magnetom-eter (2)

Solar Array (2)

Low GainAntenna (2)

Support Systems ModuleEquipment Section

AxialScienceInstrumentModule (3)andCOSTAR

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INTRODUCTION

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and the third measures thebrightness and relative positionsof stars in its field of view. Thesemeasurements, referred to asastrometry, are helping toadvance knowledge of thedistances and motions of starsand may be useful in detectingplanetary-sized companions ofother stars.

Support Systems Module

The SSM encloses the OTA andthe science instruments like thedome of an Earth-based observa-tory. It also contains all of thestructures, mechanisms, commu-nications devices, electronics andelectrical power subsystemsneeded to operate the Telescope.

This module supports the lightshield and an aperture door that,when opened, admits light. Theshield connects to the forwardshell on which the SAs and HighGain Antennas (HGA) aremounted. Electrical energy fromthe SAs charges the spacecraftbatteries to power all HSTsystems. Four antennas, twohigh-gain and two low-gain, sendand receive information betweenthe Telescope and the SpaceTelescope Operations ControlCenter (STOCC). Allcommanding occurs through theLow Gain Antennas (LGA).

Behind the OTA is the EquipmentSection, a ring of bays that housethe batteries and most of the elec-tronics, including the computerand communications equipment.At the rear of the Telescope, theaft shroud contains the scienceinstruments.

Solar Arrays

The SAs provide power to thespacecraft. They are mounted likewings on opposite sides of theTelescope, on the forward shell ofthe SSM. The SAs are rotated so

each wing’s solar cells face theSun. The cells absorb the Sun’slight energy and convert it into electrical energy to power theTelescope and charge the space-craft’s batteries, which are partof the Electrical Power Subsystem(EPS). Batteries are used whenthe Telescope moves into Earth’sshadow during each orbit.

Computers

Hubble’s Data ManagementSubsystem (DMS) contains twocomputers: the AdvancedComputer, installed duringSM3A, and the ScienceInstrument Control and DataHandling (SI C&DH) unit. TheAdvanced Computer performsonboard computations andhandles data and command trans-missions between the Telescopesystems and the ground system.The SI C&DH unit controlscommands received by thescience instruments, formatsscience data and sends data tothe communications system fortransmission to Earth.

The Hubble SpaceTelescope Program

Hubble Space Telescope repre-sents the fulfillment of a 50-yeardream and 25 years of dedicatedscientific effort and politicalvision to advance humankind’sknowledge of the universe. TheHST program comprises an inter-national community of engi-neers, scientists, contractors andinstitutions. It is managed byGSFC for the Office of SpaceScience (OSS) at NASAHeadquarters.

The program falls under theSearch for Origins and PlanetarySystems scientific theme. WithinGSFC, the program is in the FlightPrograms and Projects Directorate,under the supervision of theAssociate Director/ Program

Manager for HST. It is organizedas two flight projects: (1) theHST Operations Project and (2)the HST Development Project.

Responsibilities for scientific over-sight on HST are divided amongthe members of the Project ScienceOffice (PSO). The PSO is designedto interact effectively and effi-ciently with the HST Program andthe wide range of external organi-zations involved with the HST.The senior scientist for the HSTand supporting staff work in theOffice of the Associate Director/Program Manager for HST. Thisgroup is concerned with thehighest level of scientific manage-ment for the project. Figure 1-5summarizes the major organiza-tions that oversee the program.

The roles of NASA centers andcontractors for on-orbit servicingof the HST are:• Goddard Space Flight Center

(GSFC)—Overall managementof daily on-orbit operations ofHST and the development, inte-gration and test of replacementhardware, space support equip-ment and crew aids and tools

• Johnson Space Center (JSC)—Overall servicing missionmanagement, flight crewtraining, and crew aids and tools

• Kennedy Space Center (KSC)—Overall management of launchand post-landing operations formission hardware

• Ball Aerospace—Design, devel-opment and provision of axialscience instruments

• JPL—Design, development andprovision of WFPC1 and WFPC2

• Lockheed Martin—Personnelsupport for GSFC to accomplish(1) development, integrationand test of replacement hard-ware and space support equip-ment; (2) system integrationwith the Space TransportationSystem (STS); (3) launch andpost-landing operations and (4)daily HST operations.

Major subcontractors for SM3Binclude Goodrich Corporation,Honeywell, Jackson and Tull, Orbital Sciences Corporation,Computer Sciences Corporation,Association of Universities forResearch in Astronomy (AURA),Swales Aerospace, QSS, Creareand L-3 Communications.

The HST program requires acomplex network of communica-tions among GSFC, the Telescope,Space Telescope Ground Systemand the Space Telescope ScienceInstitute. Figure 1-6 showscommunication links.

The Value of Servicing

Hubble’s visionary modular designallows NASA to equip it with new,state-of-the-art instruments everyfew years. These servicing missionsenhance the Telescope’s sciencecapabilities, leading to fascinatingnew discoveries about theuniverse. Periodic service calls alsopermit astronauts to “tune up” theTelescope and replace limited-lifecomponents.

INTRODUCTION

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Organization

NASA HeadquartersOffice of Space ScienceDirectorate of Astronomy and Physics

Function

• Overall responsibility for the program

Space Telescope Science Institute

Goddard Space Flight Center– HST Flight Systems and Servicing Project

• Provides minute-to-minute spacecraft control• Schedules, plans and supports all science operations when required• Monitors telemetry communications data to the HST

• Selects observing programs from numerous proposals• Analyzes astronomical data

• Responsible for implementing HST Servicing Program• Manages development of new HST spacecraft hardware and service instruments• Manages HST Servicing Payload Integration and Test Program• Primary interface with the Space Shuttle Program at JSC

Goddard Space Flight Center– Office of the Associate Director/ Program Manager for HST– HST Operations Project– HST Development Project

Space Telescope OperationsControl Center

• Overall HST program management• HST project management• Responsible for overseeing all HST operations

Fig. 1-5 Organizationsummary for HSTprogram operationalphase

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Fig. 1-6 HSTdata collectingnetwork

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Starlight

Tracking andData RelaySatellite System(TDRSS)

Payload OperationsControl Center

SpaceTelescopeScienceInstitute(STScI)

Space TelescopeOperationsControl Center(STOCC)

TDRSSGroundStation

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he Hubble Space Telescope(HST) is the first observa-tory designed for extensive

maintenance and refurbishmentin orbit. Its science instrumentsand many other componentswere planned as OrbitalReplacement Units (ORU)—modular in construction withstandardized fittings and acces-sible to astronauts. Handrails,foot restraints and other built-infeatures help astronauts performservicing tasks in the Shuttlecargo bay as they orbit Earth at17,500 mph.

NASA plans to launch HSTServicing Mission 3B (SM3B) in

early 2002. The third servicingmission (SM3), originally plannedfor June 2000, had six scheduledextravehicular activity (EVA)days, followed by a reboost ofthe Telescope. However, whenthe progressive failure of severalRate Sensor Unit gyros left thespacecraft unable to performscience operations, NASA splitSM3 into two separate flights.The first flight, designated SM3Aand manifested as STS-103, waslaunched in December 1999 andincluded four scheduled EVAdays. After the flight was delayeduntil late December, NASAreduced the number of scheduledEVAs to three to ensure that the

Shuttle would be on the groundbefore the year 2000 rollover.

SM3A accomplishments includereplacement of all three RateSensor Units (six gyros), NICMOSvalve reconfiguration, installationof six Voltage/TemperatureImprovement Kits, replacementof the DF-224 Computer withthe Advanced Computer, change-out of the Fine Guidance SensorUnit-2 and mate of the associatedOptical Control ElectronicsEnhancement Kit connectors,change-out of the S-Band SingleAccess Transmitter-2, replace-ment of the Engineering/ScienceTape Recorder-3 with a Solid

HST SERVICINGMISSION 3B

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HST SERVICING MISSION 3B

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State Recorder and installation ofNew Outer Blanket Layers(NOBLs) over Bays 1, 9 and 10.

SM3B is manifested as STS-109aboard the Space ShuttleColumbia (OV-102) to belaunched to a rendezvous altitudeof approximately 315 nauticalmiles. During the planned 11-daymission, the Shuttle willrendezvous with, capture andberth the HST to the FlightSupport System (FSS). Followingservicing, the Shuttle willunberth Hubble and redeploy itto its mission orbit.

Five EVA days are scheduledduring the SM3B mission.Columbia’s cargo bay is equippedwith several devices to help theastronauts: • The FSS will berth and rotate

the Telescope. • Large, specially designed equip-

ment containers will house theORUs.

• Astronauts will work and bemaneuvered as needed from theShuttle robot arm.

SM3B will benefit from lessonslearned on NASA’s previous on-orbit servicing missions: the 1984Solar Maximum repair mission,the 1993 HST First ServicingMission (SM1), the 1997 HSTSecond Servicing Mission (SM2)and the 1999 HST ThirdServicing Mission (SM3A). NASAhas incorporated these lessons indetailed planning and trainingsessions for Columbia crewmem-bers Scott Altman, Duane Carey,Nancy Currie, John Grunsfeld,James Newman, MichaelMassimino and RichardLinnehan.

Reasons for OrbitalServicing

HST is a national asset and aninvaluable international scientificresource that has revolutionizedmodern astronomy. To achieve itsfull potential, the Telescope will

continue to conduct extensive,integrated scientific observations,including follow-up work on itsmany discoveries.

Although the Telescope hasnumerous redundant parts andsafemode systems, such acomplex spacecraft cannot bedesigned with sufficient backupsto handle every contingencylikely to occur during a 20-yearmission. Orbital servicing is thekey to keeping Hubble in oper-ating condition. NASA’s orbitalservicing plans address threeprimary maintenance scenarios:• Incorporating technological

advances into the scienceinstruments and ORUs

• Normal degradation of components

• Random equipment failure ormalfunction.

Technological Advances.Throughout the Telescope’s life,scientists and engineers haveupgraded its science instrumentsand spacecraft systems. Forexample, when Hubble waslaunched in 1990, it wasequipped with the Goddard HighResolution Spectrograph and theFaint Object Spectrograph. Asecond-generation instrument,the Space Telescope ImagingSpectrograph, took over the func-tion of those two instruments—adding considerable new capabili-ties—when it was installedduring SM2 in 1997. A slot wasthen available for the NearInfrared Camera and Multi-Object Spectrometer (NICMOS),which expanded the Telescope’svision into the infrared region ofthe spectrum. In addition, onboth SM2 and SM3A a newstate-of-the-art Solid StateRecorder (SSR) replaced anEngineering/Science TapeRecorder (E/STR). Similarly,during SM3A the original DF-224Computer was replaced with afaster, more powerful AdvancedComputer based on the Intel80486 microchip.

Component Degradation.Servicing plans take into accountthe need for routine replacements,for example, restoring HST systemredundancy and limited-life itemssuch as spacecraft thermal insula-tion and gyroscopes.

Equipment Failure. Given theenormous scientific potential ofthe Telescope—and the invest-ment in designing, developing,building and putting it intoorbit—NASA must be able tocorrect unforeseen problems thatarise from random equipmentfailures or malfunctions. TheSpace Shuttle program provides aproven system for transportingastronauts fully trained for on-orbit servicing of the Telescope.

Originally, planners consideredusing the Shuttle to return theTelescope to Earth approximatelyevery 5 years for maintenance.However, the idea was rejectedfor both technical and economicreasons. Returning Hubble toEarth would entail a significantlyhigher risk of contaminating ordamaging delicate components.Ground servicing would requirean expensive clean room andsupport facilities, including alarge engineering staff, and theTelescope would be out of actionfor a year or more—a long time tosuspend scientific observations.

Shuttle astronauts can accom-plish most maintenance andrefurbishment within a 10-dayon-orbit mission with only abrief interruption to scientificoperations and without the addi-tional facilities and staff neededfor ground servicing.

Orbital ReplacementUnits

Advantages of ORUs includemodularity, standardization andaccessibility.

Modularity. Engineers studiedvarious technical and human


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factors criteria to simplifyTelescope maintenance.Considering the limited timeavailable for repairs and theastronauts’ limited visibility,mobility and dexterity in theEVA environment, designerssimplified the maintenance tasksby planning entire componentsfor replacement.

ORUs are self-contained boxesinstalled and removed usingfasteners and connectors. Theyrange from small fuses to phone-booth-sized science instrumentsweighing more than 700 pounds(318 kg). Figure 2-1 shows theORUs for SM3B.

Standardization. Standardizedbolts and connectors also

simplify on-orbit repairs. Captivebolts with 7/16-inch, double-height hex heads hold manyORU components in place. Toremove or install the bolts, astro-nauts need only a 7/16-inchsocket fitted to a power tool ormanual wrench. Some ORUs donot contain these fasteners.When the maintenance philos-ophy changed from Earth-returnto on-orbit servicing, othercomponents were selected asreplaceable units after theirdesign had matured. This added agreater variety of fasteners to theservicing requirements, includingnon-captive 5/16-inch hex headbolts and connectors withoutwing tabs. Despite these excep-tions, the high level of standardi-zation among units reduces the

number of tools needed for theservicing mission and simplifiesastronaut training.

Accessibility. To be serviced inspace, Telescope componentsmust be seen and reached by anastronaut in a bulky pressuresuit, or they must be withinrange of an appropriate tool.Therefore, most ORUs aremounted in equipment baysaround the perimeter of thespacecraft. To access these units,astronauts simply open a large doorthat covers the appropriate bay.

Handrails, foot restraint sockets,tether attachments and othercrew aids are essential to safe,efficient on-orbit servicing. Inanticipation of such missions,

Fig. 2-1 Hubble Space Telescope Servicing Mission 3B Orbital Replacement UnitsK1175_201

31 foot-restraint sockets and 225 feet of handrails weredesigned into the Telescope. Footrestraint sockets and handrailsgreatly increase astronauts’mobility and stability, affordingthem safe worksites convenientlylocated near ORUs.

Crew aids such as portable lights,special tools, installationguiderails, handholds andportable foot restraints (PFR) alsoease servicing of Hubble compo-nents. Additionally, footrestraints, translation aids andhandrails are built into variousequipment and instrumentcarriers specific to each servicingmission.

Shuttle Support Equipment

To assist astronauts in servicingthe Telescope, Columbia will carryinto orbit several thousandpounds of hardware and SpaceSupport Equipment (SSE),including the RemoteManipulator System (RMS), FSS,Rigid Array Carrier (RAC),Second Axial Carrier (SAC) andMulti-Use LightweightEquipment (MULE) carrier.

Remote Manipulator System

The Columbia RMS, also knownas the robotic arm, will be usedextensively during SM3B. Theastronaut operating this device

from inside the cabin is desig-nated the intravehicular activity(IVA) crewmember. The RMSwill be used to:• Capture, berth and release the

Telescope• Transport new components,

instruments and EVA astro-nauts between worksites

• Provide a temporary work platform for one or both EVAastronauts.

Space Support Equipment

Ground crews will install fourmajor assemblies essential forSM3B—the FSS, RAC, SAC andMULE—in Columbia’s cargo bay(see Fig. 2-2).


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Fig. 2-2 Servicing Mission 3B Payload Bay configuration

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0 50 100 150 200 250 300

Solar Array IIStowed

Power ControlUnitReplacement(PCU-R)

Second AxialCarrier (SAC)

HST PortableFoot Restraint(PFR)

Solar Array 3Deployed 180 deg(Cell Side Up) HST Outline

MULE

LOPE

NCS Radiator

SOPE

ESM (in SoftEnclosure)

HST PortableFoot Restraint(PFR)

Flight SupportSystem (FSS)Outline

ManipulatorFoot Restraint(MFR)

Aft Fixture

NICMOS CryoCooler (NCC)

Solar Array IIStowagePlatform

Rigid ArrayCarrier (RAC)

ASIPE

AcronymsESMASIPE LOPE MULE NCS NOBL SOPE

AxialScientificInstrumentProtectiveEnclosure

ElectronicsSupportModule

Large OrbitalReplacementUnit (ORU)ProtectiveEnclosure

Multi-UseLightweightEquipmentCarrier

NICMOSCoolingSystem

Small ORUProtectiveEnclosure

New OuterBlanketLayer(StowedUnder SAC)

Inches


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Flight Support System

The FSS is a maintenance platform used to berththe HST in the cargo bay after the Columbia crewhas rendezvoused with and captured the Telescope(see Fig. 2-3). The platform was adapted from theFSS first used during the 1984 Solar Maximumrepair mission. It has a U-shaped cradle that spansthe rear of the cargo bay. A circular berthing ringwith three latches secures the Telescope to thecradle. The berthing ring can rotate the Telescopealmost 360 degrees (176 degrees clockwise or coun-terclockwise from its null position) to give EVAastronauts access to every side of the Telescope.

The FSS also pivots to lower or raise the Telescope asrequired for servicing or reboosting. The FSS’sumbilical cable provides power from Columbia tomaintain thermal control of the Telescope during theservicing mission.

Rigid Array Carrier

The RAC is located in Columbia’s forward cargo bay. Ithas provisions for safe transport to orbit of the third-generation Solar Arrays (SA3) and associated second-generation Diode Box Assemblies (DBA2), and forreturn from orbit of the second-generation Solar Arrays(SA2) and their associated Diode Box Assemblies(DBA). The RAC also includes the MLI Repair Tool,two SA2 Spines, spare PIP pins, a spareDBA2, two portable connector trays,two spare SADA Clamps, the MLI Tent,Large and Small MLI Patches, four SA2Bistem Braces, a Jettison Handle andtwo Auxiliary Transport Modules (ATM)to house miscellaneous smaller hardware(see Fig. 2-4).

Second Axial Carrier

The SAC is centered in Columbia’s cargobay. It has provisions for safe transport ofORUs to and from orbit (see Fig. 2-5). Inthe SM3B configuration:• The Advanced Camera for Surveys

(ACS) is stored in the AxialScientific Instrument ProtectiveEnclosure (ASIPE).

• The Power Control Unit (PCU)and PCU Transport Handle arestored on the starboard side.

• The NICMOS Cryo Cooler (NCC), WFPC ThermalCover and Fixed Head Star Tracker (FHST) Coversare stored on the port side.

• The NOBL Transporter (NT) contains the newprotective coverings to be installed on theTelescope equipment bay doors.

• The SAC houses other hardware, including theMLI Recovery Bag, eight Aft Shroud Latch RepairKits, Handrail Covers and Caddies, PCU HarnessRetention Device, Scientific Instrument Safety Bar,Cross Aft Shroud Harness (CASH), an Aft Fixture,two STS PFRs and an Extender, two Translation

Fig. 2-3 Flight Support System configuration – aft view

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AcronymsAMSB Advanced Mechanism Selection BoxCEP Contamination Environment PackageCMP Contamination Monitoring PackageEPDSU Enhanced Power Distribution and Switching UnitIPCU Interface Power Control UnitPDSU Power Distribution and Switching UnitPPCU Port Power Conditioning UnitSIP Standard Interface PanelSPCU Starboard Power Conditioning Unit

CEP-2

BAPS Support Post

EPDSUBracket

SIP DepartureBracket

CEP-1

Fig. 2-4 Rigid Array Carrier configuration

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SA3Forward X-Constraint

Spare PIP-PinBracket

DBA2

ATM1ATM2

SA2 Spines

CTSB

SADA CPUA

Jettison Handle

SA2 Aft Latch

SA2 ForwardLatch

Note: For clarity, MLI coversare not shown

Aids (TA), one ASIPE mini-TAand the Bays 5, 10 and DBAThermal Covers.

The protective enclosure, itsheaters and thermal insulationcontrol the temperature of thenew ORUs, providing an environ-ment with normal operatingtemperatures. Struts between theASIPE enclosure and the palletprotect Science Instruments fromloads generated at liftoff andduring Earth return.

Multi-Use Lightweight Equipment

Carrier

The MULE is located in Columbia’saft cargo bay (see Fig. 2-6). It hasprovisions for safe transport ofthe NCS Radiator, ElectronicsSupport Module (ESM), LargeORU Protective Enclosure (LOPE)and Small ORU ProtectiveEnclosure (SOPE).

Astronaut Roles and Training

To prepare for SM3B, the seven-member Columbia crew trainedextensively at NASA’s Johnson

Space Center (JSC) in Houston,Texas, and Goddard Space FlightCenter (GSFC) in Greenbelt,Maryland.

Although there has been exten-sive cross training, eachcrewmember also has trained forspecific tasks. Training forMission Commander ScottAltman and Pilot Duane Carey

focused on rendezvous and prox-imity operations, such asretrieval and deployment of theTelescope. The two astronautsrehearsed these operations usingJSC’s Shuttle Mission Simulator,a computer-supported trainingsystem. In addition, they receivedIVA training: helping the EVAastronauts into suits and moni-toring their activities outside theColumbia cabin.

The five Mission Specialists alsoreceived specific training, startingwith classroom instruction onthe various ORUs, tools and crewaids, SSE such as the RMS (therobotic arm) and the FSS.Principal operator of the roboticarm is Mission Specialist NancyCurrie, who also performs IVAduties. The alternate RMS oper-ator is Commander Altman.

Currie trained specifically forcapture and redeployment of theTelescope, rotating and pivotingthe Telescope on the FSS andrelated contingencies. Theseoperations were simulated withJSC’s Manipulator DevelopmentFacility, which includes a mockupof the robotic arm and a


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Fig. 2-5 Second Axial Carrier configuration

Fig. 2-6 Multi-Use Lightweight Equipment Carrier configuration

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K1175_206

OPA

TranslationAid

Translation Aid

EPDSU

ASLR Kits

SOPE

Aft Fixture

ASIPE

NT

2-Axis1/4-turnLatch

EVA Center Bolts

1-Axis 1/4-turnLatch

3-Axis1/4-turnLatch

NCS Radiator

ESM(Soft EnclosureShown in Phantom)

NCC(Soft Enclosure Shown in Phantom)

LOPE

PFR


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suspended helium balloon withdimensions and grapple fixturessimilar to those on theTelescope. RMS training alsotook place at JSC’s NeutralBuoyancy Laboratory (NBL),enabling the RMS operator andalternates to work with indi-vidual team members. Forhands-on HST servicing, EVAcrewmembers work in teams oftwo in the cargo bay. AstronautsJohn Grunsfeld, RichardLinnehan, James Newman andMichael Massimino loggedmany days of training for thisimportant role in the NBL, a 40-foot (12-m)-deep water tank(see Fig. 2-7).

In the NBL, pressure-suitedastronauts and their equipmentare made neutrally buoyant, acondition that simulatesweightlessness. Underwatermockups of the Telescope, FSS,RAC, SAC, MULE, RMS and theShuttle cargo bay enabled theastronauts to practice the entireSM3B EVA servicing. Suchtraining activities help the astro-nauts efficiently use the limitednumber of days (5) and duration(6 hours) of each EVA period.

Other training aids at JSChelped recreate orbital condi-tions for the Columbia crew. Inthe weightlessness of space, thetiniest movement can set instru-ments weighing several hundredpounds, such as ACS, intomotion. To simulate the delicateon-orbit conditions, models ofthe instruments are placed onpads above a stainless steel floorand floated on a thin layer ofpressurized gas. This allows crewmembers to prac-tice carefully nudging the instruments into theirproper locations.

Astronauts also used virtual reality technologies intheir training. This kind of ultrarealistic simulationenabled the astronauts to “see” themselves next tothe Telescope as their partners maneuver them intoposition with the robotic arm.

Extravehicular Crew Aids and Tools

Astronauts servicing HST use three different kindsof foot restraints to counteract the weightless envi-ronment. When anchored in a Manipulator FootRestraint (MFR), an astronaut can be transportedfrom one worksite to the next with the RMS. Usingeither the STS or HST PFR, an astronaut establishesa stable worksite by mounting the restraint to any of

Fig. 2-7 Neutral Buoyancy Laboratory at Johnson Space Center

K1175_207


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31 different receptacles placedstrategically around the Telescopeor 17 receptacles on the RAC, SAC,FSS and MULE.

In addition to foot restraints, EVAastronauts have more than 150tools and crew aids at their disposal.Some of these are standard itemsfrom the Shuttle’s toolbox whileothers are unique to SM3B. Alltools are designed for use in aweightless environment by astro-nauts wearing pressurized gloves.

The most commonly used ORUfasteners are those with 7/16-inch,double-height hex heads. Thesebolts are used with three differentkinds of fittings: J-hooks, captivefasteners and keyhole fasteners. Toreplace a unit, an astronaut uses a7/16-inch extension socket on apowered or manual ratchet wrench.Extensions up to 2 feet long areavailable to extend his or her reach.Multi-setting torque limitersprevent over-tightening of fastenersor latch systems.

For units with bolts or screws thatare not captive in the ORU frame,astronauts use tools fitted withsocket capture fittings and speciallydesigned capture tools so thatnothing floats away in the weight-less space environment. To gripfasteners in hard-to-reach areas,they can use wobble sockets.

Some ORU electrical connectorsrequire special devices, such as aconnector tool, to loosen circularconnectors. If connectors have nowing tabs, astronauts use a specialtool to get a firm hold on theconnector’s rotating ring.

Portable handles have beenattached to many larger ORUs tofacilitate removal or installation.Other tools and crew aids includetool caddies (carrying aids), tethers,transfer bags and a protective coverfor the Low Gain Antenna (LGA).

When working within theTelescope’s aft shroud area, astro-nauts must guard against opticscontamination by using specialtools that will not outgas or shedparticulate matter. All tools arecertified to meet this requirement.

Astronauts of Servicing Mission 3B

NASA carefully selected andtrained the SM3B STS-109 crew(see Fig. 2-8). Their unique set ofexperiences and capabilities makesthem ideally qualified for thischallenging assignment. Brief biog-raphies of the astronauts follow.

Scott D. Altman, NASA Astronaut (Commander, USN)

Scott Altman of Pekin, Illinois, iscommander of SM3B. He receiveda bachelor of science degree inaeronautical and astronauticalengineering from the Universityof Illinois in 1981 and a master ofscience degree in aeronauticalengineering from the NavalPostgraduate School in 1990.Altman has logged over 4000flight hours in more than 40 typesof aircraft, and over 664 hours inspace. He was the pilot on STS-90in 1998, a 16-day Spacelab flight.He also was the pilot on STS-106in 2000, a 12-day mission toprepare the International SpaceStation for the arrival of its firstpermanent crew. Altman was oneof two operators of the robot armtransporting the EVA crew duringthe STS-106 space walk. Altmanwill command the crew of STS-109for SM3B and serve as the alternateRMS operator.

Duane G. “Digger” Carey, NASA Astronaut (Lieutenant Colonel, USAF)

Duane Carey, Columbia pilot onSM3B, is from St. Paul, Minnesota.He received a bachelor of sciencedegree in aerospace engineering and

mechanics and a master of sciencedegree in aerospace engineeringfrom the University of Minnesota-Minneapolis in 1981 and 1982,respectively. Carey flew the A10Aduring tours in England, Louisianaand the Republic of Korea and theF-16 in Spain. He worked as an F-16 experimental test pilot andSystem Safety Officer at EdwardsAir Force Base. He has logged over3700 hours in more than 35 typesof aircraft. Carey was selected as anastronaut candidate by NASA in1996 and, having completed 2 yearsof training and evaluation, hasqualified for flight assignment as apilot on STS-109.

Nancy Jane Currie, Ph.D., NASA Astronaut (Lieutenant Colonel, USA)

Nancy Currie, the RMS operatoron SM3B, is from Troy, Ohio.Currie received her bachelor of artsdegree in biological science fromOhio State University in 1980, amaster of science degree in safetyfrom the University of SouthernCalifornia in 1985 and a doctoratein industrial engineering from theUniversity of Houston in 1997. AMaster Army Aviator, she haslogged 3900 flying hours in avariety of rotary and fixed wingaircraft. She was selected by NASAin 1990 and became an astronautafter completion of her training in1991. Currie has logged over 737hours in space. She was a missionspecialist on STS-57 in 1993, STS-70in 1995 and STS-88 in 1998.

John M. Grunsfeld, Ph.D., NASA Astronaut

John Grunsfeld is an astronomerand an EVA crewmember (EV1 onEVA Days 1, 3 and 5) on the SM3Bmission. He was born in Chicago,Illinois. Grunsfeld received a bach-elor of science degree in physicsfrom the Massachusetts Institute ofTechnology in 1980 and a master ofscience degree and a doctor ofphilosophy degree in physics from


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Fig. 2-8 The STS-109 mission has seven crewmembers: (clockwise from top) Commander Scott D. Altman, Pilot Duane G. “Digger” Carey, Mission Specialist Nancy Jane Currie, Mission Specialist John M. Grunsfeld,Mission Specialist Richard M. Linnehan, Mission Specialist James H. Newman and Mission Specialist Michael J. Massimino.

K1175_208


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the University of Chicago in 1984 and 1988, respec-tively. Grunsfeld reported to the Johnson Space Centerin 1992 for a year of training and became qualified forflight selection as a mission specialist. He has loggedover 835 hours in space. On his first mission, STS-67 in1995, Grunsfeld and the crew conducted observationsto study the far ultraviolet spectra of faint astronomicalobjects and the polarization of ultraviolet light comingfrom hot stars and distant galaxies. Grunsfeld flew onSTS-81 in 1997 on the fifth mission to dock withRussia’s Space Station Mir and the second to exchangeU.S. astronauts. Grunsfeld’s latest flight was aboardSTS-103 in 1999 where he performed two space walksto service Hubble on SM3A.

Richard M. Linnehan, DVM, NASA Astronaut

Rick Linnehan is a doctor of veterinary medicine andan EVA crewmember (EV2 on EVA Days 1, 3 and 5) onSM3B. He was born in Lowell, Massachusetts.Linnehan received a bachelor of science degree inAnimal Sciences from the University of NewHampshire in 1980 and his DVM degree from the OhioState University College of Veterinary Medicine in1985. Linnehan reported to the Johnson Space Centerin 1992 for a year of training and became qualified forflight selection as a mission specialist. He has logged786 hours in space. His first mission was aboard theSTS-78 Life and Microgravity Spacelab, the longestSpace Shuttle mission to date (17 days). This missioncombined both microgravity studies and a life sciencespayload. STS-90 was his second Spacelab mission.During the 16-day flight, Linnehan and the crew servedas both experimental subjects and operators for 26 indi-vidual life science experiments focusing on the effectsof microgravity on the brain and nervous system.

James H. Newman, Ph.D., NASA Astronaut

Jim Newman is an EVA crewmember (EV1 on EVADays 2 and 4) on SM3B. He was born in the TrustTerritory of the Pacific Islands (now the FederatedStates of Micronesia), but considers San Diego,California, to be his hometown. Newman received abachelor of arts degree in physics (graduating cumlaude) from Dartmouth College in 1978, and a masterof arts degree and a doctorate in physics from RiceUniversity in 1982 and 1984, respectively. Selected byNASA in 1990, Newman flew as a mission specialiston STS-51 in 1993, STS-69 in 1995 and STS-88 in1998. He has logged over 32 days in space, includingfour space walks. On STS-51, Newman and the crewdeployed the Advanced Communications TechnologySatellite and the Orbiting and Retrievable Far andExtreme Ultraviolet Spectrometer on the Shuttle PalletSatellite. On STS-69, Newman and the crew deployedand retrieved a SPARTAN satellite and the Wake Shield

Facility. On STS-88, the first International SpaceStation assembly mission, Newman performed threespace walks to connect external power and dataumbilicals between Zarya and Unity.

Michael J. Massimino, Ph.D., NASA Astronaut

Mike Massimino is an EVA crewmember (EV2 on EVADays 2 and 4) on the SM3B mission. He was born inOceanside, New York. He attended ColumbiaUniversity, receiving a bachelor of science degree inindustrial engineering with honors in 1984. He alsoreceived master of science degrees in mechanical engi-neering and in technology and policy, a mechanicalengineering degree and a doctorate in mechanical engi-neering from the Massachusetts Institute ofTechnology (MIT) in 1988, 1990 and 1992, respec-tively. Massimino was selected as an astronaut candi-date by NASA in 1996 and, having completed 2 yearsof training and evaluation, is qualified for flightassignment as a mission specialist. STS-109 will beMassimino’s first space flight, where he will performtwo space walks to service the HST.

Servicing Mission Activities

After berthing the Telescope on Flight Day 3 of SM3B,the seven-person Columbia crew will begin an ambi-tious servicing mission. Five days of EVA tasks arescheduled. Each EVA session is scheduled for 6 hours(see Fig. 2-9).

Rendezvous With Hubble

Columbia will rendezvous with Hubble in orbit 315nautical miles (504 km) above the Earth. Prior toapproach, in concert with the Space TelescopeOperations Control Center (STOCC) at GSFC,Mission Control at JSC will command HST to stowthe High Gain Antennas (HGA) and close the aperturedoor. As Columbia approaches the Telescope,Commander Altman will control the thrusters toavoid contaminating HST with propulsion residue.During the approach the Shuttle crew will remain inclose contact with Mission Control.

As the distance between Columbia and HST decreasesto approximately 200 feet (60 m), the STOCC groundcrew will command the Telescope to perform a finalroll maneuver to position itself for grappling. TheSolar Arrays (SA) will remain fully deployed parallel toHubble’s optical axis.

When Columbia and HST achieve the proper position,Mission Specialist Currie will operate the robotic armto grapple the Telescope. Using a camera mounted atthe berthing ring of the FSS platform in the cargo bay,


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she will maneuver it to the FSS, where the Telescopewill be berthed and latched.

Once the Telescope is secured, the crew will remotelyengage the electrical umbilical and switch Hubble frominternal power to external power from Columbia. PilotCarey will then maneuver the Shuttle so that the HSTSAs face the Sun, recharging the Telescope’s sixonboard nickel-hydrogen (NiH2) batteries.

Extravehicular Servicing Activities—Day by Day

Each EVA servicing period shown in Fig. 2-9 is a planning estimate; the schedule will be modified asneeded as the mission progresses. During the EVAs,HST will be vertical relative to Columbia’s cargo bay.Four EVA mission specialists will work in two-personteams on alternate days. John Grunsfeld and RickLinnehan comprise one team, and Jim Newman andMike Massimino the other.

One astronaut, designated EV1, accomplishes prima-rily the free-floating portions of the EVA tasks. Hecan operate from a PFR or while free floating. Theother astronaut, EV2, works primarily from an MFR

mounted on Columbia’s robotic arm (RMS), removingand installing the ORUs on the Hubble. EV1 assistsEV2 in removal of the ORUs and installation of thereplaced units in the SM3B carriers.

To reduce crew fatigue, EVA crewmembers swapplaces once during each EVA day: the free floatergoes to the RMS MFR and vice versa. InsideColumbia’s aft flight deck, the off-shift EVAcrewmembers and the designated RMS operatorassist the EVA team by reading out procedures andoperating the RMS.

EVA Day 1: Replace –V2 Solar Array and DiodeBox Assembly and install Diode Box Controllercross-strap harness.

At the beginning of EVA Day 1 (the fourth day of themission), the first team of EVA astronauts, Grunsfeldand Linnehan, suit up, pass through the Columbiaairlock into the cargo bay and perform the initialsetup. To prevent themselves from accidentallyfloating off, they attach safety tethers to a cablerunning along the cargo bay sills.

6-hour EVA period

EVA 1

EVA 2

EVA 3

EVA 4

UnschEVA

Contingencies (unscheduled)

EVA 5

Hubble Space TelescopeHST Development Project

SA and Diode Box-V2

HGA Deploy**

Setup:55

HST SM–3B EVA Scenario

Reboost**

r

ACS-V2

NCS/ESM-V2

PCUcleanup

SA and Diode Box+V2

PCU-V3

PCU-V3

Priority Task Times

1. RW 1:052. -V2 SA-3/Diode Box 4:352. +V2 SA-3/Diode Box 4:052. Diode Box Controller3. PCU Prep3. PCU 5:353. PCU Cleanup 0:404. ACS 2:505. NCS/ASCS (CASH) 0:155. NCS/ASCS (ESM) 1:305. NCS (NCC) 2:305. NCS (CPL and radiator) 2:356. RSU 2:307. MLI Repair 5 and 6 1:007. MLI Repair 7 and 8 1:05

RW

Close:30

NCS/NCC+V2-V3

Set:30

NCS/CPL/radiator+V2-V3

PCUPrep

PCUPrep

DBCconn

Set:15

Close:40

R.MFRPCU

Prep

PCUPrep

MFR

MFR

Set:15

Set:15

CASH

Close:30

Closeout1:00

MFR

Close:30

DBCConn

Goddard Space Flight Center

PCU

NOBL

-V3

-V2 +V2

+V3SA-3ACS

ASCS

SA-3NCS

Fig. 2-9 Detailed schedule of extravehicular activities during SM3BK1175_209


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Grunsfeld (EV1) does varioustasks to prepare for that day’sEVA servicing activities. Theseinclude deploying the ASIPEmini-Translation Aid (TA),deploying the port and starboardTAs as required, removing theMFR from its stowage locationand installing it on the RMSgrapple fixture, installing theLow Gain Antenna ProtectiveCover (LGAPC), removing theBerthing and Positioning System(BAPS) Support Post (BSP) fromits stowage location andinstalling it on the FSS, andinspecting the P105 and P106umbilical covers. Meanwhile,Linnehan (EV2) brings out of theairlock the Crew Aids and Tools(CATs) and installs the MFRhandrail to the MFR on the RMS.

The BSP is required to dampenthe vibration that the servicingactivities will induce into thedeployed SAs. Prior to the BSPinstallation, the IVA teamcommands the HST to an 85-degree pivot angle. The twocenter push-in-pull-out (PIP) pinsare installed each day andremoved each night in case theShuttle must make an emergencyreturn to Earth. EV1 removes theBSP from its stowage position inthe FSS cradle, and then installsone end to the BAPS ring with aPIP pin and the aft end to theFSS cradle with another PIP pin.Finally the BSP is commanded toits 90-degree limit and the twocenter PIP pins are installed.

After the initial setup, the EVAcrew will replace the –V2 SolarArray and Diode Box Assemblyon the Telescope. They will alsoinstall the Diode Box Controller(DBC) cross-strap harness. FirstEV1, who is free floating,retrieves the HST PFR and APEand transfers them to EV2 in theMFR. EV2 moves to the HST andinstalls the PFR on HST footrestraint receptacle 8 for the freefloater’s use. EV1 translates to

the RAC to retrieve the DBCcross-strap harness and a PortableConnector Tray, and temporarilystows them on the Telescope.Then he ingresses the PFR.Together the astronauts retractthe –V2 SA2 PrimaryDeployment Mechanism (PDM).EV1 then engages the PDM lockand installs the PortableConnector Tray. While still in thePFR, EV1 demates the SA2connectors from the DBA whileEV2 retrieves the WFPC Coverand installs it on the –V3 AftShroud in support of the PCUchange-out on EVA Day 3.

Next the astronauts remove the–V2 SA2 from the Telescope.They disengage the SADAClamp, remove SA2, translate itto the RAC and install it on thestarboard shelf via the SADAClamp and forward constraintPIP pin mechanical attachments.

EV1 translates back to theTelescope and removes the –V2DBA by disengaging theremaining X-connector drivemechanism and releasing thefour J-hook bolts while EV2retrieves the DBA2 from theRAC and translates it to EV1 atthe Telescope worksite. Theastronauts swap hardware andEV1 installs the DBA2 on theTelescope while EV2 translates tothe RAC with the DBA andinstalls it and closes its thermalcover. EV1 installs the DBCcross-strap harness onto theTelescope and mates it to the–V2 DBA2.

With the DBA2 now installed onthe Telescope, the astronautsbegin the installation work forthe replacement Solar Array.Both translate to the RAC. EV2disengages Latch 5, deploys themast and engages the two mastbolts. EV1 ingresses the aft PFR,releases and pivots Latch 3 toclear the tang, disengages thetwo tang bolts, stows the tang

and engages the two tang bolts.EV2 disengages Latch 2. EV1pivots Latch 3 to the stowedposition and installs the PIP pin,deploys the MLI flap over thetang interface and releases Latch4. EV1 stabilizes SA3 while EV2releases Latch 1. The astronautsthen remove SA3 from the RAC.

Both crewmembers install SA3onto the Telescope by properlyorienting SA3 and inserting theSADA into the SADA Clampuntil the three soft dock tangsengage. EV1 engages the SADAClamp closed and mates the SA3electrical interfaces. EV2 trans-lates back to the RAC andperforms the SA2 close-out work:engaging the aft latch, theforward latch and the twoforward constraint bolts.

Then the astronauts deploy theSA3 panel, engage the panellocking bolts and release the SA3brake. EV1 routes the DBC cross-strap harness to the +V2 side,removes the HST PFR andtemporarily stows it on theASIPE, and removes and stows aPortable Connector Tray on theRAC. Meanwhile, EV2 maneu-vers to the –V3 aft shroud andinstalls the two FHST covers inpreparation for the PCU change-out on EVA Day 3.

At this time, the astronautsperform the MFR swap:Grunsfeld ingresses the MFR andLinnehan becomes the free floater.EV1 (the free floater) translates tothe ASIPE, retrieves the PFR fromtemporary stowage and transfersit to EV2, who installs it in footrestraint receptacle 19 in prepara-tion for EVA Day 2. EV1 retrievesthe Bay 10 Thermal Cover andinstalls it over Bay 10 of theTelescope while EV2 disengagesand removes the Telescope’s +V2trunnion EPS panel, mates theDBC cross-strap harness andinstalls an MLI tent over the EPSpanel cavity.


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For the daily close-out, EV1inspects the FSS main umbilicalmechanism, disengages the twocenter PIP pins on the BSP,retracts the mini-TA, retracts theport and starboard TAs ifrequired, and takes a tool inven-tory. Meanwhile EV2 preparesthe CATs installed on the MFRhandrail for return into theairlock and egresses the MFR.EV1 releases the MFR safetytether from the grapple fixturefor contingency Earth return.After completing the EVA Day 1tasks, both astronauts return tothe airlock and perform theairlock ingress procedure.

EVA Day 2: Replace +V2 SolarArray and Diode BoxAssembly and Reaction WheelAssembly – 1 (RWA-1)

During EVA Day 2, Newman(EV1) and Massimino (EV2) willreplace the +V2 Solar Array andDiode Box Assembly on theTelescope and complete the DBCinstallation by mating it to the+V2 SA3. They also will replacethe RWA-1.

Fewer daily setup tasks arerequired for EVA Day 2 than forEVA Day 1. After completing theairlock egress procedure, EV1reconnects the safety strap on theMFR, installs the two BSP centerPIP pins and deploys the mini-TA. EV2 exits the airlock withthe EVA Day 2 required CATsinstalled on the MFR handrailand installs the MFR handrail.

After completing the daily setuptasks, the astronauts begin thetasks for the +V2 Solar Arrayand Diode Box Assemblychange-outs, which are similarto the –V2 Solar Array andDiode Box Assembly change-outsperformed during EVA Day 1.First EV1 and EV2 retrieve theHST PFR and APE and installthem on HST foot restraintreceptacle 19. EV1 translates to

the RAC to retrieve a PortableConnector Tray and temporarilystows it on the Telescope. Thenhe ingresses the PFR.

Together the astronauts retractthe +V2 SA2 PDM. EV1 thenengages the PDM lock andinstalls the Portable ConnectorTray. Still in the PFR, EV1demates the SA2 connectorsfrom the DBA while EV2 disen-gages five of six bolts on eachdoor of Telescope Bays 2, 3 and 4in support of the PCU change-out on EVA Day 3.

Next the astronauts remove the+V2 SA2 from the Telescope.They disengage the SADAClamp, remove SA2, translate itto the RAC and install it on theport shelf via the SADA Clampand forward constraint PIP pinmechanical attachments.

EV1 translates back to theTelescope and removes the +V2DBA by disengaging the remainingX-connector drive mechanism andreleasing the four J-hook boltswhile EV2 retrieves the DBA2 fromthe RAC and translates it to EV1 atthe Telescope worksite. The astro-nauts swap hardware and EV1installs the DBA2 on the Telescopewhile EV2 translates to the RACwith the DBA and installs it andcloses its thermal cover.

With the +V2 DBA2 nowinstalled on the Telescope, theybegin installation work for thereplacement Solar Array. Bothastronauts translate to the RAC.EV2 disengages Latch 5, deploysthe mast and engages the twomast bolts. EV1 ingresses theforward PFR, releases and pivotsLatch 3 to clear the tang, disen-gages the two tang bolts, stowsthe tang and engages the two tangbolts. EV2 disengages Latch 2.EV1 pivots Latch 3 to the stowedposition and installs the PIP pin,deploys the MLI flap over the tanginterface and releases Latch 4.

EV1 stabilizes SA3 while EV2releases Latch 1. Both removeSA3 from the RAC.

Working together, the astronautsinstall SA3 onto the Telescope byproperly orienting SA3 andinserting the SADA into theSADA Clamp until the three softdock tangs engage. EV1 engagesthe SADA Clamp closed andmates the SA3 electrical inter-faces, then mates the DBC cross-strap harness to the +V2 DBA2.EV2 translates back to the RACand performs the SA2 close-outwork: engaging the aft latch, theforward latch and the twoforward constraint bolts.

Both astronauts work togetheragain to deploy the SA3 panel,engage the panel locking boltsand release the SA3 brake (seeFig. 2-10). EV1 removes the HSTPFR and APE and stows them onthe FSS, and removes and stowsthe Portable Connector Tray onthe RAC.

Upon completion of the SAchangeout task, the EVA crewwill replace the RWA-1. EV1translates to the LOPE on the aftstarboard side of the MULE,opens the lid, removes the twoRWA1-R wing tab connectorsfrom the LOPE pouch andsecures them to the RWA1-Rhandle Velcro, disengages thethree keyway bolts, removes thereplacement RWA-1 (RWA1-R)and translates to the top of thestarboard MULE.

EV2 maneuvers to Bay 6 andopens the Bay 6 door, dematesthe two RWA-1 wing tab heaterconnectors from the heaterbracket, demates the two RWA-1wing tab connectors from RWA-1, disengages the three RWA-1 keyway bolts andremoves RWA-1 from HST Bay 6.Then he maneuvers to the starboard MULE location andperforms an RWA swap with EV2.


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EV1 maneuvers with RWA1-R to the Bay 6 worksite,installs it on HST, engages the three keyway boltsand mates the four wing tab electrical connectors.Then he closes the Bay 6 door.

After transferring the RWA1-R to EV2 and receivingRWA-1 from EV2, EV1 translates back to the LOPE,installs the RWA-1 in the LOPE, engages the threekeyway bolts, stows the two wing tab connectors inthe LOPE pouch and closes the LOPE lid.

EV1 retrieves the Bay 5 Thermal Cover and installsit in the retracted position on the Telescope Bay 5 inpreparation for the PCU change-out on EVA Day 3.EV1 also retrieves the doorstop extensions andinstalls them on the +V2 aft shroud doorstops inpreparation for the NCS Radiator installation onEVA Day 5.

For the daily close-out, EV1 inspects the FSS mainumbilical mechanism, disengages the two center PIPpins on the BSP, retracts the mini-TA, retracts theport and starboard TAs if required and takes a toolinventory. Meanwhile EV2 prepares the CATsinstalled on the MFR handrail for return into theairlock and egresses the MFR. EV1 releases the MFRsafety tether from the grapple fixture for contin-gency Earth return. After completing the EVA Day 2tasks, both astronauts return to the airlock andperform the airlock ingress procedure.

EVA Day 3: Replace PCU.

During EVA Day 3, Grunsfeld (EV1) and Linnehan(EV2) will replace the PCU in the Telescope Bay 4.After the airlock egress procedure, EV1 reconnectsthe safety strap on the MFR, installs the two BSPcenter PIP pins and deploys the mini-TA. EV2 exitsthe airlock with the EVA Day 3 required CATsinstalled on the MFR handrail and installs the MFRhandrail.

Both astronauts complete the daily setup tasks, thenbegin the PCU change-out. EV1 translates to theRAC to retrieve the Power Distribution Unit (PDU)fuse plug caddy and battery stringers and transfersthem to EV2. EV2 translates to the Telescope Bay 3,opens the bay door, demates the three batteryconnectors, installs caps to deadface the batterypower and temporarily closes the door. He thentranslates to Bay 2 and performs the same procedurefor the Bay 2 battery.

Meanwhile EV1 translates to Bay 5 and deploys thethermal cover, retrieves the DBA thermal cover,translates to the +V2 DBA2 and installs its thermalcover. Then he translates to Bay 10 and deploys thethermal cover, retrieves the DBA thermal cover,translates to the -V2 DBA2 and installs its thermalcover. EV1 deploys the FHST covers on theTelescope, then translates to the SAC, retrieves theHarness Retention Device and transfers it to EV2 atthe Bay 4 worksite.

EV2 opens the Bay 4 door and installs the HarnessRetention Device and door stay. EV2 removes the sixinboard PDU Fuse Plugs to gain sufficient access tothe PCU connectors on the left side. EV1 retrievesthe PCU handhold from the SAC and temporarilystows it by the +V2 trunnion. Then he translates tothe airlock and recharges his suit with oxygen,enabling him to extend his EVA time. EV2 disen-gages seven of 10 PCU keyway bolts and demates allbut the last six connectors (30).

At this point, EV1 and EV2 perform the MFRswap. EV2 completes demating the remainingPCU connectors, installs the PCU handhold,disengages the three remaining bolts, disengagesthe PCU groundstrap and removes the PCU fromthe Telescope.

EV1 translates to the starboard SAC where thereplacement PCU (PCU-R) is located, ingresses thePFR, opens the thermal cover, disengages the sixkeyway bolts and removes the PCU-R from the SAC.

Fig. 2-10 Deployment of new rigid solar array

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EV1 and EV2 swap boxes at the SAC worksite. EV2translates with the PCU-R back to the Telescopeworksite, installs it, engages seven keyway bolts andengages the groundstrap (see Fig. 2-11). EV1 stowsthe PCU on the SAC, engages the six keyway bolts,retightens the two PCU handhold wing bolts,egresses the PFR and reinstalls the PCU thermalcover. He then translates to the airlock and rechargeshis suit with oxygen. EV2 mates the 36 connectorson the PCR-R, a difficult and time-consuming task.

EV1 inspects the Telescope exterior handrails to beused for the ACS and NCS tasks on EVA Days 4 and5 and, if required, installs handrail covers. EV2 rein-stalls the PDU fuse plugs, removes the HarnessRetention Device, removes the door stay and closesthe Bay 4 door with one J-bolt. He re-opens the Bay 3 door, remates the battery connectors andcloses the door with one J-bolt. Then he performsthe same procedure for the Bay 2 battery. After thePDU fuse plugs are reinstalled, EV1 translates to the+V2 DBA2, retrieves the thermal cover, stows it onits Bay 5 thermal cover stowage pouch and retractsthe Bay 5 thermal cover. He translates to the -V2DBA2, retrieves the thermal cover, stows it on itsBay 10 thermal cover stowage pouch and retracts theBay 10 thermal cover. Next EV1 retrieves theHarness Retention Device and stows it on the SAC.Then he retracts the FHST covers, receives the PDUfuse plug caddy and battery stringers from EV2, andstows them on the RAC. If time allows, EV2removes the WFPC thermal cover and stows it onthe SAC.

For the daily close-out, EV1 inspects the FSS mainumbilical mechanism, disengages the two center PIPpins on the BSP, retracts the mini-TA, retracts theport and starboard TAs if required and takes a toolinventory. Meanwhile EV2 prepares the CATsinstalled on the MFR handrail for return into theairlock and egresses the MFR. EV1 releases the MFRsafety tether from the grapple fixture for contin-gency Earth return. After the completion of the EVADay 3 tasks, both astronauts return to the airlockand perform the airlock ingress procedure.

EVA Day 4: Replace FOC with ACS, install ESMand perform PCU cleanup tasks.

During EVA Day 4, Newman (EV1) andMassimino (EV2) will replace the Faint ObjectCamera (FOC) with the ACS, install the ESM inthe Telescope aft shroud and do the remainingPCU cleanup tasks. After the airlock egress proce-dure, EV1 reconnects the safety strap on theMFR, installs the two BSP center PIP pins anddeploys the mini-TA. EV2 exits the airlock withthe EVA Day 4 required CATs installed on theMFR handrail and installs the MFR handrail.

The astronauts complete the daily setup tasks,then begin the FOC/ACS change-out. EV1 deploysthe aft fixture, retrieves the COSTAR Y-harnessfrom the RAC port ATM and stows it on theTelescope aft shroud. EV2 opens the –V2 aftshroud doors. EV1 and EV2 work together toremove the FOC from the Telescope. EV1 dematesthe four FOC connectors, disconnects the FOCpurge line and disconnects the groundstrap. EV2disengages the FOC A-Latch and EV1 disengagesthe FOC B-Latch. Then EV2 removes the FOCfrom the Telescope and stows it on the aft fixture.

EV1 and EV2 now work together to install theCASH. Even though the CASH is part of the NCSinstallation, it is installed now to maximize EVAtimeline efficiencies and eliminate the need to openthe –V2 aft shroud doors a second time on EVA Day 5.EV1 and EV2 retrieve the CASH from the SAC andinstall it on handrails inside the aft shroud. EV1 and EV2 retrieve the ACS from the ASIPE. EV1configures the aft ASIPE PFR, opens the ASIPE lid,disconnects the ACS groundstrap and deploys the B-Latch alignment aid. EV2 disengages the A-Latchand EV1 disengages the B-Latch. They both removethe ACS from the ASIPE. EV1 closes the ASIPE lidand engages one lid latch to maintain thermalstability inside the ASIPE. The astronauts continue towork together to install the ACS into the Telescopeaft shroud (see Fig. 2-12). They insert the ACS alongthe guiderails, deploy the B-Latch alignment aid arm,

Fig. 2-11 Change-out of Power Control Unit

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engage the B-Latch and A-Latch, stow the alignmentaid, tether the ESM groundstrap to the ACS handrail,reinstall the HST groundstrap and mate the four ACSconnectors.

Next the astronauts install the FOC into the ASIPE.EV2 retrieves the FOC from the aft fixture whileEV1 re-opens the ASIPE lid. EV2 inserts the FOCinto the ASIPE guiderails while EV1 stows the aftfixture and engages the FOC B-Latch. EV2 engagesthe A-Latch. EV1 disengages the FOC groundstrapbolt and installs the groundstrap on FOC, thencloses the ASIPE lid and engages the five lid latches.

After completing the FOC installation into the ASIPE,the astronauts perform the MFR swap. They retrievethe ESM from the MULE and install it in the –V2 aftshroud. Then they install the ACS ESM groundstrapon the ESM, retrieve the Y-harness from temporarystowage, demate the four COSTAR connectors, matefour Y-harness connectors to the COSTAR harnesses,mate four Y-harness connectors to COSTAR andmate four Y-harness connectors to the ESM. EV2mates the four CASH connectors to the ESM. Nowthey are ready to close the –V2 aft shroud doors.

The PCU cleanup task follows the FOC/ACSchange-out and the ESM installation. EV1 removesthe Bay 10 thermal cover and stows it on the ASIPE,then removes the Bay 5 thermal cover and stows iton the ASIPE. He also articulates the aft ASIPE PFRto its landing configuration. Meanwhile, EV2engages the remaining five J-bolts on each door of

Bays 2, 3 and 4. Then the astronauts remove theFHST and WFPC covers from the Telescope andstow them on the SAC.

For the daily close-out, EV1 inspects the FSS mainumbilical mechanism, disengages the two center PIPpins on the BSP, retracts the mini-TA, retracts theport and starboard TAs if required and takes a toolinventory. Meanwhile EV2 prepares the CATsinstalled on the MFR handrail for return into theairlock and egresses the MFR. EV1 releases the MFRsafety tether from the grapple fixture for contin-gency Earth return. After completing the EVA Day 4tasks, both astronauts return to the airlock andperform the airlock ingress procedure.

EVA Day 5: Install the NCC and NCS Radiator.

During EVA Day 5, Grunsfeld (EV1) and Linnehan(EV2) will install the remaining NCS hardware.After the airlock egress procedure, EV1 reconnectsthe safety strap on the MFR, installs the two BSPcenter PIP pins and deploys the mini-TA. EV2 exitsthe airlock with the EVA Day 5 CATs installed onthe MFR handrail and installs the MFR handrail.

Both astronauts complete the daily setup tasks,then begin the NCS installation. EV2 opens theTelescope +V2 aft shroud doors while EV1 retrievesthe Cryo Vent Line (CVL) bag and NCS sock bagfrom the RAC port ATM and the NCC groundstrapand cryo vent insert from the RAC starboard ATM.Together the astronauts prepare the NICMOS forthe NCS installation. They remove the NICMOSCVL and stow it in the CVL bag, close the NICMOSvent line valve, disengage the NICMOS groundstrapfrom NICMOS, install the NCC groundstrapadapter on NICMOS and install the cryo ventinsert. EV1 retrieves the P600 harness from theRAC starboard ATM. EV2 retrieves the NCC fromthe SAC and opens the neon bypass valve whileEV1 closes the NCC contamination cover.

Both astronauts install the NCC into the Telescopeaft shroud. EV2 installs the NCC groundstrap onNCC and mates the four CASH connectors. EV1translates to the MULE and releases some of theNCS Radiator latches and shear ties. At this point,they perform the MFR swap.

Next comes retrieval of the NCS Radiator. EV1closes the left aft shroud door and together withEV2 disengages the remaining latches, removes the NCS Radiator from the MULE and opens theNCS Radiator handrail latches. They install theNCS Radiator onto the exterior of the Telescope aft shroud.


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Fig. 2-12 Installation of the Advanced Camera for Surveys

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EV1 prepares the NCC by installing the coolant inand coolant out cryo valve heaters and neon lineswhile EV2 installs the NCC power cable to the EPStest panel and reinstalls theMLI tent. They install theNCS Radiator conduitthrough the cryo vent insertopening in the aft bulkheadand engage the cryo ventinsert latches and lockingbolts (see Fig. 2-13). Thenthe NCS Radiator harnessesare mated to the NCS, theNCC saddle thermal coveropened and the CPL evapo-rator removed from thesock and tethered to thebulkhead standoff by EV1.EV2 opens the NCSRadiator diode box, checkssome LEDs and switches,and closes the diode boxcover. He installs the CPLevaporator in the saddle,installs the saddle cover,engages its two bolts andcloses the NCC saddlethermal cover. Together theastronauts close the aftshroud doors. The crew willthen stow the CVL andNCS sock bags in the RACport ATM.

The final close-out procedure follows the NCS instal-lation. EV1 inspects the FSS main umbilical mecha-nism and the P105/P106 covers, removes the LGAprotective cover from the Telescope and reinstalls iton the FSS, disengages the two center PIP pins on theBSP, retracts the mini-TA, retracts the port and star-board TAs (if required) to their landing configura-tions and takes a tool inventory. Meanwhile EV2prepares the CATs installed on the MFR handrail forreturn into the airlock, egresses the MFR andperforms the MFR stow procedure. After completingthe EVA Day 5 tasks, both astronauts return to theairlock and perform the airlock ingress procedure.

Possible EVA Day 6: Replace RSU, install NOBLs5, 6, 7 and 8, and install ASLR kits if needed.

While there is no scheduled EVA Day 6 on the mani-fest, if all goes well during EVA Days 1 through 5and the Columbia consumables are adequate, theastronauts may execute a sixth EVA day to changeout an RSU, install the Bays 5, 6, 7 and 8 NOBLs,and install repair kits on the aft shroud doors, if anyof the latches exhibited excessive running torqueupon examination on EVA days 4 and 5.

EVA Contingency Day. An unscheduled EVA dayhas been allocated for enhancing payload mission

Fig. 2-13 Installation of NICMOS Cooling System radiator

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Fig. 2-14 Redeploying the Hubble Space Telescope


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success and for any payloadrequirements on the HST rede-ployment day.

Redeploying the Telescope. Theday following EVA Day 5 will be devoted to any unscheduledEVA tasks and redeployment of the HST into Earth orbit (seeFig. 2-14). The SAs are slewed tothe Sun to generate electricalpower for the Telescope and tocharge the batteries, and HGAsare commanded to their deployedposition. When the batterycharging is complete, the RMSoperator guides the robotic armto engage HST’s grapple fixture.The ground crew commandsHubble to switch to internalpower. This accomplished,crewmembers commandColumbia’s electrical umbilical todemate from Hubble and openthe berthing latches on the FSS.If any Telescope appendages failto deploy properly, two missionspecialists can perform EVAtasks, manually overriding anyfaulty mechanisms.

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he launch and deploymentof NASA’s Hubble SpaceTelescope (HST) ushered in

a golden era of space explorationand discovery. For nearly 12years, Hubble’s rapid-fire rate ofunprecedented discoveries hasinvigorated astronomy. Notsince the invention of the tele-scope four centuries ago has ourvision of the universe changedso radically in such a shortstretch of time.

As the 12.5-ton Earth-orbitingobservatory looks into spaceunburdened by atmosphericdistortion, new details aboutplanets, stars and galaxies come

into crystal clear view. TheTelescope has produced a vastamount of information and asteady stream of images thathave astounded the world’s astro-nomical and scientific communi-ties. It has helped confirm someastronomical theories, challengedothers and often come up withcomplete surprises for whichtheories do not yet exist.

Hubble was designed to providethree basic capabilities:• High angular resolution—the

ability to image fine detail• Ultraviolet performance—the

ability to produce ultravioletimages and spectra

• High sensitivity—the ability todetect very faint objects.

Each year NASA receives over athousand new observingproposals from astronomersaround the world. Observingcycles are routinely over-subscribed by a factor of six.

The Telescope is extremelypopular because it allows scien-tists to get their clearest viewever of the cosmos and to obtaininformation on the temperature,composition and motion of celes-tial objects by analyzing the radiation they emit or absorb.Results of HST observations

HST SCIENCE and DISCOVERIES

T

HST SCIENCE AND DISCOVERIES

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are being presented regularly in scientific papers atmeetings of the American Astronomical Society andother major scientific conferences.

Although Hubble’s dramatic findings to date are toonumerous to be described fully in this MediaReference Guide, the following paragraphs highlightsome of the significant astronomical discoveries andobservations in three basic categories:• Formation and evolution of stars and planets• Earth’s Solar System• Galaxies and cosmology.

For further information, visit the Space TelescopeScience Institute website at http://oposite.stsci.edu.

Evolution of Stars and Planets

It’s a cruel world for some fledgling planets. Hubblefound an inhospitable neighborhood for embryonicplanets in the Orion Nebula, a stellar breeding groundpeppered with hot, massive stars whose blistering radi-ation erodes material around them. The Telescope alsohunted for planets in a nearby globular cluster andfound none, although up to 50 detections wereexpected. But Hubble did find a vast stellar nursery inthe Large Magellanic Cloud.

Probing the universe since April 24, 1990, Hubblehas chased after planets, snapped pictures of themost luminous known star and chronicled the explo-sive death of a massive star.

Elusive Planets

Scanning 35,000 stars in the tightly packed globularstar cluster 47 Tucanae, the Telescope was on theprowl for planets (see Fig. 3-1). Surprisingly, it foundnone. However, the results do not rule out the possi-bility that the cluster could contain normal solarsystems like ours that the Telescope cannot detect.

Hubble can detect only Jupiter-sized planets orbitingclose to their parent stars—closer than the scorchedplanet Mercury. These star-hugging planets completean orbit and pass in front of their parent stars everyfew days. Nevertheless, the finding suggests that theconditions for planet formation and evolution maybe fundamentally different in the cluster than in ourgalactic backyard.

Searching for planets in 47 Tucanae, 15,000 light-years away, was not easy. Planets at that distance aretoo dim to be seen directly. So astronomers used anindirect method to detect the planets, pushing the

Fig. 3-1 A vast "city" of stars in 47 Tucanae K1175_301


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Telescope to the limit of its capabilities. Among the 35,000 stars, astronomers looked for a slightdimming of a star due to a planet passing in front of it, an event called a transit. The planet had to be slightly larger than Jupiter, our solar system’slargest planet, to block enough light for Hubble to detect it.

Why didn’t the Telescope find any Jupiter-sizedplanets? One reason is that the stars are packedtogether so tightly that the gravity of nearby starsstripped nascent planets from their parent stars.Another possibility is that a torrent of ultravioletradiation from the earliest and biggest stars mayhave boiled away fragile embryonic dust disks outof which planets would have formed.

In a star-forming region a few thousand light-yearscloser to Earth, planets are playing a life-and-deathgame of survival. Hubble produced the first directvisual evidence for the growth of planet “buildingblocks” inside dust disks around dozens of stars inthe Orion Nebula (see Fig. 3-2).

Planetary building blocks are large grains, ranging insize from smoke particles to sand grains. To makeplanets, these grains stick together. Hubble observa-tions show that it may be easy to begin buildingplanets deep inside the star-forming cloud.Reaching adulthood, however, may be a hazardousprocess. Fledgling planets try to form quickly beforethey are destroyed by blistering ultraviolet radiationfrom the nebula’s brightest star, Theta 1 Orionis C.

Fig. 3-2 Planetary nurseries under fire in Orion K1175_302


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Astronomers predict that 90 percent of the youngestdisks—which started out being billions of milesacross—will be destroyed within 100,000 years. Butplanet formation will continue in the disks shieldedfrom the deadly radiation. These stars probably willbecome the parents of a variety of planets.

Stars Under Construction

The telescope has snapped a panoramic portrait of avast, sculpted landscape of gas and dust wherethousands of stars are being born (see Fig. 3-3).This fertile star-forming region, called the 30Doradus Nebula, has a sparkling stellar centerpiece:

the most spectacular cluster of massive stars in ourcosmic neighborhood of about 25 galaxies.

The mosaic picture shows that ultraviolet radiationand high-speed material unleashed by the stars inthe cluster, called R136 (the large blue blob left ofcenter), are weaving a tapestry of creation anddestruction, triggering the collapse of looming gasand dust clouds and forming pillar-like structuresthat are incubators for nascent stars.

The view offers an unprecedented, detailed look atthe entire inner region of 30 Doradus, measuring200 light-years wide by 150 light-years high. The

Fig. 3-3 Vast star-forming region in 30 Doradus Nebula K1175_303


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nebula resides in the Large Magellanic Cloud (asatellite galaxy of the Milky Way), 170,000 light-years from Earth.

Nebulas like 30 Doradus are the “signposts” ofrecent star birth. High-energy ultraviolet radia-tion from the young, hot, massive stars in R136causes the surrounding gaseous material to glow.Previous Hubble telescope observations showedthat R136 contains several dozen of the mostmassive stars known, each about 100 times themass of the Sun and about 10 times as hot. Thesestellar behemoths all formed at the same timeabout 2 million years ago.

Most Luminous Star

Astronomers used Hubble’s probing “eye” to findwhat may be the most luminous known star—acelestial mammoth that releases up to 10 milliontimes the power of the Sun and is big enough tofill the diameter of Earth’s orbit. Called the PistolStar, this stellar behemoth unleashes as muchenergy in 6 seconds as the Sun does in 1 year (seeFig. 3-4). The image, taken with the Telescope’sinfrared camera, also reveals a bright nebula,created by extremely massive stellar eruptions.The nebula is so big (4 light-years) it would nearlyspan the distance from the Sun to Alpha Centauri,the star nearest to Earth’s solar system.

Fig. 3-4 A brilliant star at the Milky Way’s core K1175_304


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When the titanic star formed 1 to 3 million yearsago, astronomers estimate that it may have weighedup to 200 times the mass of the Sun before sheddingmuch of its bulk in violent eruptions. The star isapproximately 25,000 light-years from Earth near thecenter of the Milky Way Galaxy.

When massive stars die, they don’t go quietly.Instead, they end their lives with mammoth explo-sions. Hubble has been watching one of these explo-sions, supernova 1987A. A ground-based telescopefirst saw the star’s self-destruction in February 1987.

In July 1997 Hubble’s imaging spectrograph capturedthe first images of material ejected by the explodingstar as they slammed into an inner ring around thedying object. A 100-billion-mile-wide knot of gas in apiece of the ring has already begun to “light up” asits temperature surges from a few thousand degreesto a million degrees Fahrenheit. By analyzing thisglowing ring, astronomers may find clues to many ofthe supernova’s unanswered mysteries: What was

the progenitor star? Was it a single star or a binarysystem? The ring was formed 20,000 years ago beforethe star exploded. What process created it? Thesupernova is 167,000 light-years away in the LargeMagellanic Cloud.

Earth’s Solar System

A comet disintegrating as it looped around the Sun.Another comet slamming into Jupiter. Auroras on Jupiter and Saturn. Wacky weather on Mars.

Hubble has kept an “eye” on our solar system.

Death of a Comet

From July to August 2000, the orbiting observatoryprovided unprecedented close-up views of the demiseof Comet LINEAR as the icy body passed around theSun (see Fig. 3-5). The mountain-sized object brokeapart during the summer of 1999. Hubble pictures

Fig. 3-5 Hubble discovers missing pieces of Comet LINEAR K1175_305


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support the popular theory that comets are composedof clusters of small, icy bodies called “cometesimals,”which date to the early solar system.

In July 2000 the Telescope first noticed the cometfalling apart when it fortuitously saw a piece of theicy body blow off and sail along its wispy tail.Following the comet’s closest approach to the Sun onJuly 26, astronomers using ground-based telescopesreported that the comet had vanished. Butastronomers employing Hubble discovered that thecomet had disintegrated into a cadre of “mini-comets”with tails, each perhaps tens of feet across. The groupof objects resembled a shower of glowing balls fromfireworks.

Astronomers believe that the Sun’s heat caused thecomet to distintegrate. By studying how the cometfell apart, astronomers hope to learn how it was puttogether about 4.6billion years ago.

Crash on Jupiter

In 1994 the Telescopewatched pieces of acomet invade Jupiter. Itrecorded 21 fragmentsof Comet Shoemaker-Levy 9 slamming intothe giant planet. Aseach comet fragmentcrashed into Jupiter,Hubble caught mush-room-shaped plumesalong the edge of theplanet. The largest frag-ment impact created anEarth-sized bull’s-eyepattern on Jupiter.

The Telescope’s probeof the comet’sbombardment,combined with resultsfrom other space-borneand Earth-based tele-scopes, sheds new light on Jupiter’s atmosphericwinds and its immense magnetic field. Hubble’s sharpimages show that the fragments, the largest of whichwere probably a few miles across, did not break upcatastrophically before plunging into Jupiter’s atmos-phere. This reinforces the notion that solid, massivebodies produced the comet’s atmospheric explosions.

Mars Close-up

In 2001 Hubble captured the best view of Mars everobtained from Earth (see Fig. 3-6). Frosty white waterice clouds and swirling orange dust storms above avivid rusty landscape reveal Mars as a dynamicplanet.

The picture was taken on June 26 when Mars wasapproximately 43 million miles (68 million km) fromEarth—the closest Mars has been to Earth since 1988.Details as small as 10 miles (16 km) across can be seen.The colors have been carefully balanced to give a real-istic view of Mars’ hues as they might appear througha ground-based telescope.

Especially striking is the large amount of seasonaldust storm activity seen in the image. One largestorm system is churning high above the northern

polar cap and asmaller dust stormcloud can be seennearby. Anotherlarge dust storm isspilling out of thegiant Hellasimpact basin inthe SouthernHemisphere.

Hubble hasobserved Marsbefore, but neverin such detail. Thebiennial closeapproaches ofMars and Earthare not all thesame. BecauseMars’ orbit aroundthe Sun ismarkedly ellip-tical, the closeapproaches toEarth can rangefrom 35 million to63 million miles.

Astronomers study the changeable surface andweather conditions on Mars, in part, to help plan fortwo NASA missions to land rovers on the planet’ssurface in 2004. The Mars opposition of 2001 servesas a prelude for 2003 when Mars and Earth will comewithin 35 million miles of each other, the closest since1924 and not to be matched until 2287.

Fig. 3-6 Mars at opposition in 2001 K1175_306


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Dances of Light

Hubble also studied auroras—curtains of light—thatseem to dance above the north and south poles ofSaturn and Jupiter. Astronomers used the Telescope’sultraviolet-light camera, the imaging spectrograph,to probe these auroras.

Saturn’s auroras rise more than 1,000 miles abovethe cloud tops. Its auroral displays are caused by anenergetic wind from the Sun that sweeps over theplanet, much like Earth’s aurora. But Saturn’sauroras can be seen only in ultraviolet light, which isinvisible from Earth. These auroras are primarilyshaped and powered by a continual tug-of-war

between Saturn’s magnetic field and the flow ofcharged particles from the Sun.

The Telescope took many images of Jupiter ’sauroras, including some in ultraviolet light. Jovianauroral storms develop when electrically chargedparticles trapped in the magnetic field surroundingthe planet spiral inward at high energies towardthe north and south magnetic poles. When theseparticles hit the upper atmosphere, they exciteatoms and molecules there, causing them to glow(the same process that makes streetlights shine).Jupiter ’s auroras are caused, in part, by particlesspewed out by volcanoes on Io, one of Jupiter ’smoons (see Fig. 3-7).

Fig. 3-7 Auroral storms on Jupiter K1175_307


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Galaxies and Cosmology

To find the most distant exploding star ever seen,Hubble gazed far across the cosmos and discovered abewildering zoo of galaxies that existed in the earlyuniverse. Looking closer to Earth, the Telescopesnapped pictures of clusters of young stars born in thewreckage of colliding galaxies and helped astronomersmeasure the universe’s expansion rate by takingpictures of a special class of pulsating star. UsingHubble, astronomers also conducted a census of morethan 30 galaxies to study the relationship betweengalaxies and their black holes. These observations shedlight on how the universe behaves and how galaxieswere formed.

"Dark Energy"

In 2001 the Telescope’s discovery of the farthestexploding star ever found bolstered the case for theexistence of a mysterious form of “dark energy” in theuniverse. The exploding star is a supernova, whicherupted in a faraway galaxy 10 billion years ago. Theconcept of dark energy, which shoves galaxies awayfrom each other at an ever-increasing speed, was firstproposed, and then discarded, by Albert Einstein inthe early 1900s.

This Hubble discovery also reinforced the startlingidea that the universe only recently began speedingup, a finding made in 1998 when the unusually dimlight of several distant supernovas suggested theuniverse is expanding more quickly than in the past.The light from this 10-billion-year-old supernovaoffered the first tantalizing observational evidencethat gravity began slowing down the universe’s expan-sion after the Big Bang. Only later did the repulsiveforce of dark energy win out over gravity’s attractivegrip. Astronomers made the discovery by analyzinghundreds of images of ancient galaxies taken byHubble in infrared and visible light.

Black Holes

Hubble also looked at scores of galaxies to study therelationship between galaxies and their black holes.Using Hubble’s Space Telescope Imaging Spectrograph,astronomers conducted a census of more than 30galaxies. Evidence suggests that monstrous black holeswere not born big but instead grew on a measureddiet of gas and stars controlled by the host galaxies.The finding supports the idea that a titanic black holedid not precede a galaxy’s birth. Instead it co-evolvedwith the galaxy by trapping about 0.2 percent of themass of the galaxy’s bulbous hub of stars and gas.

This means that black holes in small galaxies wentrelatively undernourished, weighing in at a fewmillion solar masses. Black holes in the centers ofgiant galaxies, some tipping the scale at over a billionsolar masses, were so engorged with infalling gas thatthey once blazed as quasars, the brightest objects inthe cosmos.

The bottom line is that the final mass of a black holeis not primordial; it is determined during the galaxyformation process. Galaxies are the largest assem-blages of stars in the universe: billions of stars boundtogether by the mutual pull of gravity.

Starburst Galaxies

Most galaxies form new stars at a fairly slow rate, butmembers of a rare class known as starburst galaxiesblaze with extremely active star formation. Scientistsusing Hubble’s WFPC2 are perfecting a technique todetermine the history of starburst activity in galaxiesby using the colors of star clusters. Measuring the clus-ters’ colors yields information about stellar tempera-tures. Since young stars are blue and older stars morered, the colors can be related to their ages, similar tocounting the rings in a fallen tree trunk in order todetermine the tree’s age.

Galaxy NGC 3310 is forming clusters of new stars at a prodigious rate (see Fig. 3-8). NGC 3310 has severalhundred star clusters, visible as bright blue diffuseobjects that trace the galaxy’s spiral arms. Each starcluster represents the formation of up to about amillion stars, a process that takes less than 100,000years. Hundreds of individual young, luminous starsalso can be seen throughout the galaxy.

Once formed, the star clusters become redder with ageas the most massive and bluest stars exhaust their fueland burn out. Measurements of the wide variation incluster colors show that they range in age from about1 million up to more than 100 million years. This sug-gests that the starburst “turned on” over 100 millionyears ago, perhaps triggered when a companion galaxycollided with NGC 3310.

Hubble’s observations may change astronomers’view of starbursts. They once thought starbursts tobe brief episodes, resulting from catastrophic eventslike a galactic collision. However, the wide range ofcluster ages in NGC 3310 suggests that once trig-gered the starbursting can continue for an extendedinterval.


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Stellar Kindergartens

NGC 4013 is a spiral galaxy, similarto the Milky Way, lying some 55million light-years from Earth in thedirection of the constellation UrsaMajor. Viewed pole-on, NGC 4013would look like a nearly circularpinwheel. From Earth, however, ithappens to be seen edge-on. Even at55 million light-years, the galaxy islarger than Hubble’s field of view andthe image shows only a little morethan half of the object, albeit withunprecedented detail (see Fig. 3-9).

Dark clouds of interstellar dust standout because they absorb the light ofbackground stars. Most of the cloudslie in the plane of the galaxy,forming a dark band about 500 light-years thick, which appears to cut thegalaxy in two from upper left tolower right. When light passesthrough a volume containing smallparticles (for example, molecules inthe Earth’s atmosphere or interstellar

dust particles in galaxies), it becomesfainter and redder. By studying the colorand the amount of light absorbed bythese distant clouds in NGC 4013,astronomers can estimate the amountof matter in them. Individual cloudscontain as much as 1 million times theamount of mass in the Sun.

Astronomers believe that new stars areformed in these dark interstellar clouds.Later, when the dust disperses, theyoung stars become visible as clusters ofblue stars. NGC 4013 shows severalexamples of these stellar kindergartensnear the center of the image in Fig. 3-9,lying in front of the dark band along thegalaxy’s equator. (The extremely brightstar near the upper left corner is anearby foreground star belonging to theMilky Way, which lies in the line ofsight to NGC 4013.)

The Evolving Universe

Studying galaxies falls into the realm ofcosmology, the study of the evolution ofthe universe on the largest scale. Bylooking at the distribution of galaxies in

Fig. 3-9 Spiral galaxy NGC 4013 viewed edge-on K1175_309

Fig. 3-8 Galaxy NGC 3310 ablaze with active star formation K1175_308


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space, Edwin P. Hubble discovered that the universe is expanding. He found that galaxies were rushingaway from each other at a rate proportional to theirdistance: those farthest away were receding thefastest. The measured value for this expansion rateis called the Hubble constant.

Measuring the Hubble constant was one of the threemajor goals for the Telescope before it was launched in 1990. In May 1999 the Hubble Space Telescope Key Project team announced that it had completed its efforts to measure precise distances to far-flunggalaxies, an ingredient needed to determine the age,size and fate of the universe. The team measured theHubble constant at 70 km/sec/mpc with an uncer-tainty of 10 percent. This means that a galaxy appearsto be moving 160,000 mph faster for every 3.3 millionlight-years away from Earth.

The team used the Telescope to observe 18 galaxies,some as far away as 65 million light-years. They werelooking for Cepheid variable stars, a special class ofpulsating star used for accurate distance measure-ments. Almost 800 were discovered. But the teamcould only pick out Cepheids in nearby and interme-diate-distance galaxies. To calculate distances to far-flung galaxies, they used “secondary” distance meas-urements, such as a special class of exploding starcalled a Type Ia supernova.

Combining the Hubble constant measurement withestimates for the density of the cosmos, the teamdetermined that the universe is approximately 12 billion years old if its expansion rate is constant or decelerating somewhat under the influence ofgravity. But if the expansion rate is accelerating, asscientists now believe, the universe is older, perhaps 14 billion years. The team also determined that theuniverse does not have enough bulk to halt the expansion of space.

Summary

The Hubble Space Telescope has established itself as apremier astronomical observatory that continues tomake dramatic observations and discoveries at theforefront of astronomy. Following the successful Firstand Second Servicing Missions, the Telescope hasachieved all of its original objectives. Among a longlist of achievements, Hubble has:• Improved our knowledge of the size and age of the

universe• Provided decisive evidence of the existence of super-

massive black holes at the centers of galaxies• Clearly revealed the galactic environments in which

quasars reside• Detected objects with coherent structure (proto-

galaxies) close to the time of the origin of theuniverse

• Provided unprecedentedly clear images and spectraof the collision of Comet Shoemaker-Levy 9 withJupiter

• Detected a large number of protoplanetary disksaround stars

• Elucidated the various processes by which starsform

• Provided the first map of the surface of Pluto• Routinely monitored the meteorology of planets

beyond Earth’s orbit• Made the first detection of an ultraviolet high-

energy laser in Eta Carinae.

After Servicing Mission 3B, the Telescope will viewthe universe anew with significantly expanded scien-tific capabilities from the new ACS and a reactivatedNICMOS. These additions, and the upgrades toHubble’s operating hardware, promise other momentous discoveries in the years ahead.

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hree instruments are inactive scientific use on theHubble Space Telescope:

• Wide Field and PlanetaryCamera 2 (WFPC2)

• Space Telescope ImagingSpectrograph (STIS)

• Fine Guidance Sensor 1R(FGS1R), designated as theprime FGS for astrometricscience.

Other instrument bays are occu-pied by the Near Infrared Cameraand Multi-Object Spectrometer(NICMOS), now dormant due tothe depletion of its solid nitrogencryogen; the Faint Object Camera(FOC), an obsolete instrument

that has been decommissioned;and COSTAR, a corrective opticaldevice no longer needed.

During HST Servicing Mission3B (SM3B), the FOC will bereplaced by the AdvancedCamera for Surveys (ACS). Inaddition, an experimentalmechanical cooling system willbe attached to NICMOS to deter-mine if it can be brought backinto operation. COSTAR willremain in place until HSTServicing Mission 4 (SM4) whenit will be removed to make roomfor the Cosmic OriginsSpectrograph (COS).

Hubble’s three FGSs are under-going a systematic program ofrefurbishment and upgrading. Oneach servicing mission, one FGSis being replaced, returned to theground, disassembled and refur-bished, then taken back to HSTto become the replacement unitfor the next FGS to be serviced.The final refurbished FGS will beinstalled during SM4.

Advanced Camera for Surveys

Astronauts will install theAdvanced Camera for Surveys(ACS), in the Telescope duringSM3B. ACS is a collaborative

SCIENCE INSTRUMENTS

T

SCIENCE INSTRUMENTS

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effort of Johns HopkinsUniversity, the NASAGoddard Space FlightCenter, Ball Aerospaceand the Space TelescopeScience Institute.

The primary purpose ofthis third-generationinstrument (see Fig. 4-1) isto increase the discoveryefficiency of imaging withHST. ACS will provide acombination of detectorarea and quantum effi-ciency surpassing thatavailable from currentinstruments by a factor of10. It consists of threeindependent channels withwide-field, high-resolutionand ultraviolet (UV)imaging capability and anassortment of filtersdesigned for a broad rangeof scientific goals.

ACS will be five timesmore sensitive than theWFPC2 and will havemore than twice itsviewing field. The ACS’swide field of view (FOV),high throughput mirrorswith higher reflectivityand larger, more sensitivedetectors dramaticallyimprove the Telescope’sability to deliver valu-able science data.

Wide Field Channel. The high sensitivity and widefield of the ACS Wide Field Channel (WFC) in visibleand red wavelengths will make it the instrument ofchoice for imaging programs. Sky surveys with theWFC will study the nature and distribution ofgalaxies. Scientists should be able to set firm limits onthe number of galaxies in the universe and determineprecisely the epoch of galaxy formation. Its red-lightsensitivity will allow the WFC to observe old anddistant galaxies whose spectra are red-shifted due tothe expansion of the universe.

High Resolution Channel. The ACS HighResolution Channel (HRC) will take extremelydetailed pictures of the inner regions of galaxies andsearch neighboring stars for planets and protoplane-

tary disks. ACS has a coronograph that can suppresslight from bright objects, enabling the HRC toobserve fainter targets nearby, such as the galacticneighborhoods around bright quasars. The HRC willallow astronomers to view the light at the centers ofgalaxies containing massive black holes as well asmore prosaic galaxies, star clusters and gaseousnebulas. With its excellent spatial resolution, theHRC also can be used for high-precision photometryin stellar population programs.

Solar Blind Channel. The ACS Solar Blind Channel(SBC) blocks visible light to enhance Hubble’s visionin the UV portion of the spectrum. Some features—such as emission lines that indicate the presence ofcertain molecules—can be detected only in the UV.The SBC uses a highly sensitive photon-counting

Weight 875 pounds (397 kg)

Dimensions 3 x 3 x 7 feet (0.9 x 0.9 x 2.2 m)

Principal investigator Dr. Holland Ford, Johns Hopkins University

Prime contractor Ball Aerospace

Wavelength range 115 – 1050 nanometers

Spectral Range(Nanometers)

Detector ArraySize (Pixels)

Pixel Size(Microns)

Field of Vie(Arcsec)Channel

Wide Field 350 – 1050 4096 x 4096 15 x 15 200 x 204

High Resolution 200 – 1050 1024 x 1024 21 x 21 26 x 29

Solar Blind 115 – 180 1024 x 1024 25 x 25 26 x 29

Fig. 4-1 Advanced Camera for Surveys (ACS) configurationK1175_401

HRC/SBCCalibrationPlatform

HRC ShutterMechanism

ElectricalInterfaceConnectors

HRC Detector

WFCDetector

WFC ShutterMechanism

WFC/HRCFilter Wheels

SBC Detector

IM2 and M2CorrectorMirrors

SBC Filter Wheel

HRCCorrectorMechanism,M1 WFC

Corrector Mechanism, IM1

M3 FoldMechanism

IM3 CorrectorMirror

CalibrationDoor –CoronagraphMechanism

MEB (1 of 2)

"Y" Fitting

"B" Fitting

OpticalBench

BaffleBaffle

Enclosure

CEBs

SCIENCE INSTRUMENTS

detector to enhance the visibility of these features. Thischannel will search for hot stars and quasars and studyauroras and weather on planets in our solar system.

Physical Description

ACS will reside in an axial bay behind the HST mainmirror. It is designed to provide HST with a deep,wide-field survey capability. The primary design goalof the ACS WFC is to achieve a factor of 10 improve-ment in discovery efficiency compared to WFPC2.Discovery efficiency is defined as the product ofimaging area and instrument throughput.

In addition, ACS also provides:• Grism spectroscopy: low resolution (R~100) wide-

field spectroscopy from 5500 to 11,000 Å, availablein both the WFC and the HRC.

• Objective prism spectroscopy: low resolution (R~100at 2000 Å) near-UV spectroscopy from 2000 to 4000 Å, available in the HRC.

• Objective prism spectroscopy: low resolution(R~100 at 1216 Å) far-UV spectroscopy from1150 to 1700 Å, available in the SBC.

• Coronography: aberrated beam coronography inthe HRC from 2000 to 11,000 Å with 1.8arcsecond- and 3.0 arcsecond-diameter occultingspots.

• Imaging polarimetry: polarimetric imaging in theHRC and WFC with relative polarization angles of0, 60 and 120 degrees.

ACS Optical Design

The ACS design incorporates two main opticalchannels: one for the WFC and one shared bythe HRC and SBC. Each channel has inde-pendent corrective optics to compensate forHST’s spherical aberration. The WFC has threeoptical elements, coated with silver to optimizeinstrument throughput in visible light. Thesilver coatings cut off at wavelengths short of3700 Å. The WFC has two filter wheels sharedwith the HRC, offering the possibility ofinternal WFC/HRC parallel observing for somefilter combinations. Figure 4-2 shows the WFCoptical design. Figure 4-3 shows the HRC/SBCoptical chain, which comprises three aluminizedmirrors overcoated with magnesium fluoride.

The HRC and SBC are selected by means of aplane fold mirror (M3 in Fig. 4-3). To select theHRC, the fold mirror is inserted into theoptical chain so that the beam is imaged ontothe HRC detector through the WFC/HRCfilter wheels. To select the SBC, the foldmirror is moved out of the beam to yield a

two-mirror optical chain that images through theSBC filter wheel onto the SBC detector. To accessthe aberrated beam coronograph, a mechanism isinserted into the HRC optical chain. This mecha-nism positions a substrate with two occulting spotsat the aberrated telescope focal plane and anapodizer at the re-imaged exit pupil.

Fig. 4-2 ACS Wide Field Channel optical design

K1175_402From OTA

IM2

IM3IM1


WFC Detector

X

YZ

Fig. 4-3 ACS High Resolution/Solar Blind Channels optical design

K1175_403

HRC Detector

From OTA X

YZ

M1

M2

SBCFilter Wheel

SBCMAMA

M3Fold Mirror


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SCIENCE INSTRUMENTS

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Filter Wheels

ACS has three filter wheels: two shared by the WFCand HRC and one dedicated to the SBC. TheWFC/HRC filter wheels contain the major filter setssummarized in Fig. 4-4. Each wheel also contains oneclear WFC aperture and one clear HRC aperture.Parallel WFC and HRC observations are possible forsome filter combinations, unless the user disables thisoption or the parallel observations cannot be addedbecause of timing considerations. Note: Since the filterwheels are shared, it is not possible to independentlyselect the filter for WFC and HRC parallel observa-tions. Figure 4-5 shows the SBC filters.

Observations

With its wider field of view, superb image quality andexquisite sensitivity, ACS will take full advantage ofHubble’s unique position as a space-based telescope.ACS sees in wavelengths ranging from ultraviolet tothe far red (115 to 1050 nanometers). The new instru-ment is actually a set of three different, specializedchannels. Each plays a unique imaging role, enablingACS to contribute to many different areas of astronomy and cosmology.

Among the observations ACS will undertake are:• Searching for extra-solar planets• Observing weather and aurorae on planets in our

own solar system• Conducting vast sky surveys to study the nature and

distribution of galaxies• Searching for galaxies and clusters of galaxies in the

early universe• Searching for hot stars and quasars• Examining the galactic neighborhoods around bright

quasars.

Near Infrared Camera and Multi-ObjectSpectrometer

NICMOS is a second-generation instrument installedon the HST during SM2 in 1997. Its cryogen wasdepleted in 1998. During SM3B astronauts will installthe NICMOS Cooling System (NCS), which uses anew technology called a Reverse Brayton-CycleCryocooler (see Fig. 4-6).

This type of mechanical cooler allows longer opera-tional lifetimes than current expendable cryogenicsystems. The attempt to revive NICMOS with NCS isviewed as an experimental application of a promisingnew technology. There is no guarantee that NICMOSwill return to full, normal science operation. However,the importance of the science enabled by NICMOSmakes the “experiment” well worth the effort.

NCS has three fluid loops:• Circulator loop• Primary cooling loop• Capillary Pumped Loop (CPL).

Gas circulates first in the circulator loop between thecooling system and the inside of the NICMOS cryo-stat, carrying heat away from the cryostat and keepingthe detectors at their operating temperature (73 Kelvinor -200˚C).

The primary cooling loop is the heart of the NICMOScryocooler. It contains a compressor, a turboalternatorand two heat exchangers. This loop implements areverse-Brayton thermodynamic cycle, providing thecooling power for the entire system. Generating thiscooling power also produces a significant amount ofheat (up to 500 watts). The CPL carries the heat awayfrom the primary cooling loop. It connects the mainheat-generating component, the compressor, with anexternal radiator that radiates the heat into space. Theheat is removed by evaporating ammonia on the hotend of the CPL and recondensing it at the cold end.

Filter Type Description

Medium band Lyman-Alpha

Long pass MgF2, CaF2, BaF2, quartz, fused silica

Objective prisms LiF, CaF2

Fig. 4-5 SBC filters

K1175_405

Filter Type Filter Description Channel

Broadband Sloan Digital Sky Survey (SDSS) WFC/HRCB, V, Wide V, R, I WFC/HRCNear-UV HRC

Narrowband Ha (2%), [OIII] (2%), [NII] (1%) WFC/HRCNeV (3440 Å) HRCMethane (8920 Å) HRC/[WFC*]

Ramp filters 2% bandpass (3700 – 10700 Å) WFC/HRC9% bandpass (3700 – 10700 Å) WFC/HRC

Spectroscopic Grism WFC/HRCPrism WFC/HRC

Polarizers Visible (0 deg, 60 deg, 120 deg) HRC/[WFC*]Near-UV (0 deg, 60 deg, 120 deg) HRC/[WFC*]

*Limited field of view for filters using WFC

Fig. 4-4 ACS CCD filters

K1175_404

The Electronics Support Module(ESM) controls the major func-tions of the NCS. It contains an8051 microprocessor that imple-ments control laws for coolerfunctions, including compressor,turboalternator and circulatorspeed. It also controls the CPLreservoir temperatures, regulatingthe quantity of heat transportedto the radiator. In the background,the ESM collects and monitorscritical NCS telemetry and generalhousekeeping telemetry, and relayscommands to the NCS subsytems.

Instrument Description

NICMOS is an all-reflective imag-ing system: near–room-temperatureforeoptics relay images to three focalplane cameras contained in a cryo-

genic dewar system (see Fig. 4-7).Each camera covers the same spec-tral band of 0.8 to 2.5 microns witha different magnification and anindependent filter wheel. They look

at different segments of the HSTFOV simultaneously. Figure 4-8 lists the cameras and their opticalcharacteristics.

SCIENCE INSTRUMENTS

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Fig. 4-6 NICMOS Cooling System (NCS) K1175_406

Circulator Filter From NICMOS Cryostat

To NICMOS Cryostat

Cold Load Interface

Turboalternator

Valve

Electronics

Compressor

Electrical Connector

Compressor Filter

Z

X

Y

Circulator

Accumulator (2)

Recuperator

Kevlar SupportStrap (3)

Circulator LoopGas Fill Bottle

Circulator LoopHigh Pressure Tank

Heat RejectionInterface

PressureTransducers

Fig. 4-7 Near Infrared Camera and Multi-Object Spectrometer (NICMOS)

"C" Fitting

"A" Fitting

TECI Radiators

Cryo Interface

Aperture

Enclosure

DewarBench

MainElectronicsCompartment

ElectricalInterface

OpticsK1175_407

SCIENCE INSTRUMENTS

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Light entering the instrument entrance aperture falls ona flat folding mirror and is redirected to a sphericalmirror. It is then re-imaged on the corrective mirror,which is mounted to an offset pointing mechanism.This mirror corrects the HST spherical aberration andalso has a cylindrical deformation to correct for astig-matism in the optical path.

Next the corrected image is relayed to a three-mirrorfield-dividing assembly, which splits the light intothree separate, second-stage optical paths. In additionto the field-dividing mirror, each second-stage opticuses a two-mirror relay set and a folding flat mirror.

The field-dividing mirrors are tipped to divide thelight rays by almost 4.5 degrees. The tip allows phys-ical separation for the two-mirror relay sets for eachcamera and its FOV. The curvature of each mirrorallows the required degree of freedom to set the exitpupil at the cold mask placed in front of the filterwheel of each camera.

A corrected image is produced in the center of theCamera 1 field mirror. Its remaining mirrors areconfocal parabolas with offset axes to relay the imageinto the dewar with the correct magnification andminimal aberration.

Cameras 2 and 3 have different amounts of astigma-tism because their fields are at different off-axis pointsfrom Camera 1. To correct the residual astigmatism,one of the off-axis relay mirrors in Camera 3 is ahyperbola and one of the relay mirrors in Camera 2 is an oblate ellipsoid. Camera 2 also allows a corona-graphic mode by placing a dark spot on its field-dividing mirror. During this mode the HST is maneu-vered so that the star of observation falls within theCamera 2 field-dividing mirror and becomes occultedfor coronagraphic measurements.

All the detectors are 256 x 256-pixel arrays of mercurycadmium telluride (HgCdTe) with 40-micron pixel-to-

pixel spacing. An independent, cold filter wheel isplaced in front of each camera and is rotated by room-temperature motors placed on the externalaccess port of the dewar.

A multilevel, flat-field illumination system correctsdetector nonuniformities. The light source and associ-ated electronics are located in the electronics section at the rear of the instrument. IR energy is routed to the optical system using a fiber bundle. The fiberbundle illuminates the rear of the corrector mirror,which is partially transparent and fits the aperturefrom the fiber bundle. The backside of the element iscoarsely ground to produce a diffuse source.

The instrument structural enclosure houses all oper-ating components in two individual compartments:optics and electronics. A graphite-epoxy optical bench,kinematically mounted within the enclosure, separatesthe two compartments. The foreoptics and the cryo-genic dewar mount to the bench. The electronicscontrol the thermal environment, partly through radiators mounted to the outboard enclosure panels. A combination of active proportional heaters, selectivesurface finishes and multilayer insulation (MLI) maintains the temperature.

Optical paths penetrate the dewar in three places.Each camera port consists of an external vacuum shell window, an internal heat-blocking window and a cold mask to prevent the detectors from seeingwarm structure. Each camera has an independentlycontrolled filter wheel. Warm stepper motors mountedon the vacuum shell turn the filter wheels, mountedon the vapor-cooled shell. Graphite-epoxy, thin-walledtubes are used for the drive shafts connecting thewarm motors to the cold wheels. The drive shaftsprovide torsional rigidity for accurately positioningthe filter in the optical path while maintaining lowthermal conductivity.

NICMOS Specifications

Figure 4-9 shows the NICMOS specifications. Threedetector cables and three detector clock cables routeelectrical signals from the cryogen tank to thehermetic connector at the vacuum shell. The cablesconsist of small-diameter, stainless-steel wiremounted to a polymeric carrier film. They areshielded to minimize noise and crosstalk betweenchannels. (Shielding is an aluminized polyester filmincorporated into drain wires.) The cables also havelow thermal conductivity to minimize parasitic heat loads. In addition, two unshielded cablesconnect to thermal sensors used during fill andfor on-orbit monitoring.

Parameter

Total field (arcsec)

Pixel size (arcsec)

Magnification

f number

Camera 1

11.0

0.043

3.33

80.0

Camera 2

19.2

0.075

1.91

45.7

Camera 3

51.2

0.20

0.716

17.2

Fig. 4-8 NICMOS optical characteristicsK1175_408

SCIENCE INSTRUMENTS

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Besides processing signals from and controlling thedetectors, the electronics prepare data for transmis-sion to the HST computer, respond to groundcommands through the HST and control operation of the instrument. NICMOS uses an onboard 80386microprocessor with 16 megabytes of memory forinstrument operation and data handling. Twosystems are provided for redundancy. The detectorcontrol electronics subsystem includes a micro-processor dedicated to operation of the focal planearray assemblies. Two microprocessors are providedfor redundancy.

ObservationsA restored NICMOS will provide IR imaging andlimited spectroscopic observations of astronomicaltargets between 1.0 and 2.5 microns. It will extendHST’s capabilities into the near IR, generating high-resolution images for detailed analysis of:• Prostellar clouds, young star clusters and brown

dwarfs• Obscured active galaxy nuclei• Temporal changes in planetary atmospheres• Young protogalaxies• Supernovae at high redshift used to time the

acceleration of the expansion of the universe.

Space Telescope ImagingSpectrograph

STIS was developed under the direction of theprincipal investigator, Dr. Bruce E. Woodgate,jointly with Ball Aerospace. The spectrograph (seeFig. 4-10) was designed to be versatile and effi-cient, taking advantage of modern technologies toprovide a new two-dimensional capability to HSTspectroscopy. The two dimensions can be usedeither for “long slit” spectroscopy, where spectra of many different points across an object areobtained simultaneously, or in an echelle mode,

at very high spectral resolution, to obtain morewavelength coverage in a single exposure. STIS alsocan take both UV and visible images through alimited filter set.

During SM2 astronauts installed STIS as a replace-ment for the Goddard High Resolution Spectrographand the Faint Object Spectrograph. Its capabilitiesinclude coverage of a broader wavelength range intwo dimensions, coronagraphs and high time-resolution in the UV. It also can image and provideobjective prism spectra in the intermediate UV. STIS carries its own aberration-correcting optics.


STIS resides in an axial bay behind the HST mainmirror. Externally, the instrument measures 7.1 x 2.9 x2.9 feet (2.2 x 0.98 x 0.98 m) and weighs 825 pounds(374 kg). Internally, STIS consists of a carbon fiberoptical bench, which supports the dispersing optics and three detectors (see Fig. 4-11).

The spectrograph has been designed to work in three different wavelength regions, each with its owndetector. Some redundancy is built into the designwith overlap in the detector response and backup spectral modes. A mode selection mechanism (MSM)is used to select a wavelength region or mode. TheMSM has 21 optical elements: 16 first-order gratings(including six order-sorting gratings used in the echellemodes), an objective prism and four mirrors. Theoptical bench supports the input corrector optics,focusing and tip/tilt motions, input slit and filterwheels, and MSM.

Light from the HST main mirror is first corrected andthen brought to a focus at the slit wheel. After passing

Weight 861 lb (391 kg) in flight configurationDimensions 7.1 x 2.8 x 2.8 feet (2.2 x 0.88 x 0.88 m)Principal investigator Dr. Rodger I. Thompson, U. of ArizonaContractor Ball AerospaceField of view 51.2 x 51.2 arcsec

19.2 x 19.2 arcsec11.0 x 11.0 arcsec

Detectors 3 HgCdTe arrays

256 x 256 pixels

Near Infrared Camera and Multi-ObjectSpectrometer (NICMOS)

Fig. 4-9 NICMOS specifications

K1175_409

K1175_410

Main ElectronicsBoxes (MEB 1 and 2)

Grating WheelAssembly

CorrectorMirror

Optical Bench

Calibration InputMechanism

Correction Mirror and MechanismSlit Wheel Assembly

Collimation MirrorMode Isolation Shutter

Echelle (4)Echelle Blocker

CCD DetectorCCD Shutter

CCDElectronicsBox

MAMA Detectors

Calibration SubsystemCamera Mirror (5)

Fig. 4-10 Space Telescope Imaging Spectrograph

SCIENCE INSTRUMENTS

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through the slit, it is collimated by a mirror onto oneof the MSM optical elements. A computer selects themode and wavelength. The MSM rotates and nutatesto select the correct optical element, grating, mirror orprism and points the beam along the appropriateoptical path to the correct detector.

For first-order spectra, a first-order grating is selected forthe wavelength and dispersion. The beam then ispointed to a camera mirror, which focuses the spectrumonto the detector, or goes directly to the detector itself.

For an echelle spectrum, an order-sorting grating thatdirects the light to one of the four fixed echelle gratingsis selected, and the dispersed echellogram is focused viaa camera mirror onto the appropriate detector. Thedetectors are housed at the rear of a thermallycontrolled optical bench where they can easily dissipateheat through an outer panel. An onboard computercontrols the detectors and mechanisms.

STIS has three detectors, each optimized for aspecific wavelength region.• Band 1, covering the wavelengths from 115 to 170 nm,

uses a Multi-Anode Microchannel Plate Array(MAMA) with a cesium iodide (CsI) photocathode.

• Band 2, from 165 to 310 nm, also uses a MAMAbut with a cesium telluride (CsTe) photocathode.

• Bands 3 and 4, from 305 to 555 nm and 550 to1000 nm, use the same detector, a charge-coupleddevice (CCD).

Entrance Apertures. After a light beam passesthrough the corrector, it enters the spectrographthrough one of several slits. The slits are mounted ona wheel and can be changed by wheel rotation.

There also are camera apertures of 50 x 50 and 25 x25 arcsec. Some have occulting bars incorporated.The telescope can be positioned to place bright starsbehind the occulting bars to allow viewing and

For bright object projection, the calibration insert mechanism is placed in the light pathto act as a shutter and block light from the OTA from reaching the MAMA detectorsCalibration lamps and optical train are

not shown but are in the general area– For line lamps, see camera mode

for lamp placement– For flat field lamps, see gross

calibration mode for lampreplacement

Note: Internal bafflingnot shown

Note: Echelle blocker is usedto block echelles whenfirst-order or direct imagingmodes are being used

Note: For low-resolution modes, thecamera mirror and grating elementare combined into a single optic onthe mode select mechanism

Hole-in the-Mirror Lamp– For slit illumination and

wavelength calibrations infirst-order modes

Calibration Insert Mechanism– For flat field lamps and

wavelength calibrations inechelle and X-dispenser modes

– When inserted in light path, themechanism acts as a shutter andblocks light from the OTA fromreaching the MAMA detectors

CCD FoldMirror

MAMA1Echelles

MAMA1Fold Mirror

CCD Shutter(Closed)

CCD CameraMirror

MAMA2 EchellesCamera Mirror

MAMA1 EchellesCamera Mirror

Corrector Mechanism(Tilt and Focus)

MAMA 2 First Order MediumResolution Camera Mirror

Mode SelectMechanism(MSM)

SecondCorrectorMirror

Input Optical Pathfor All Modesfor All Detectors

CollimationMirror

MAMA2Fold Mirror

MAMA2Detector

MAMA1Detector

Mode IsolationShutter(Closed)

MAMA2Echelles

Echelle Blocker(Block MAMA1Position)MAMA1 First Order

Medium ResolutionCamera Mirror

CCD

Slit Wheel

Fig. 4-11 STIS components and detectors

K1175_411

SCIENCE INSTRUMENTS

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observation of faint objects in the FOV. In addition,there is a special occulting mask or coronagraph—afinger in the aperture that can be positioned over abright star to allow examination of any faint mate-rial nearby. In effect, it simulates a total eclipse of a nearby star. This mode is particularly useful tosearch for faint companion stars or planetary disksaround stars.

Mode Selection Mechanism. The MSM is a rotatingwheel with 16 first-order gratings, an objective prismand four mirrors. Its axis is a shaft with two inclinedouter sleeves, one sleeve fitting inside the other. Thesleeves are constructed so that rotation of one sleeverotates a wheel to orient the appropriate optic intothe beam. Rotation of the second sleeve changes theinclination of the wheel axis or the tilt of the opticto select the wavelength range and point the dis-persed beam to the corresponding detector. One of three mirrors can be selected to take an image of an object.

Multi-Anode Microchannel Plate Array Detectors.For UV modes, STIS employs two types of MAMAdetectors. A photocathode optimizes each detector toits wavelength region. Each detector’s photocathodeprovides maximum sensitivity in the wavelengthregion selected while it rejects visible light notrequired for the observations.

The heart of each MAMA detector is a microchannelplate (MCP)—a thin disk of glass approximately 1.5 mmthick and 5 cm in diameter that is honeycombedwith small (12.5-micron) holes or pores. The frontand back surfaces are metal coated. When a voltageis applied across the plate, an electron entering anypore is accelerated by the electric field. It eventuallycollides with the wall of the pore, giving up itskinetic energy to liberate two or more secondaryelectrons. (The walls are treated to enhance thesecondary electron production effect.) The secondaryelectrons continue down the pore and collide withthe wall, emitting more electrons, and so the processcontinues, producing a cascade of a million electronsat the end of the pore.

The anode array is a complex fingerlike pattern.When electrons strike certain anodes, a signal is sentto the computer memory indicating the position andtime of arrival of the photon. Figure 4-12 shows thedetection scheme in simplified form.

Only 132 circuits are required to read out all 1024 x1024 pixels (picture elements) in the anode array. Asthe MAMA records the arrival of each photon, it canprovide a time sequence. For instance, if an object isvarying in time, like a pulsar, the data can be displayedto show if there is any periodicity. To create an image,data must be integrated in the computer memorybefore it is displayed. The MAMA data is recorded toa time resolution of 125 microseconds.

Fig. 4-12 Simplified MAMA system K1175_414

Photon

Photocathode

Microchannel Plate (MCP)

Anode Array

Memory

e_

e_

Cloud

ChargeAmplifiers

DecodeElectronics

DecodeElectronics

MemoryTiming and

Control

SCIENCE INSTRUMENTS

4-10

When used in the normal mode, each detector has1024 x 1024 pixels, each 25 x 25 microns square.However, data received from the anode array can beinterpolated to give a higher resolution, splitting eachpixel into four 12.5 x 12.5 micron pixels. This isknown as the high-resolution mode. It provides higherspatial resolution for looking at fine structural detailsof an object and ensures full sampling of the opticalimages and spectra. Data taken in high-resolutionmode can be transformed to normal resolution.

Charge-Coupled Detector. The STIS CCD wasdeveloped at Scientific Imaging Technologies (SITe)with GSFC and Ball input. Fabricated using inte-grated circuit technology, the detector consists oflight-sensitive pixels deposited onto a thin wafer ofcrystalline silicon. Each element is 21 x 21 microns.The elements are arranged 1024 to a row in 1024columns for a total of 1,048,576 pixels.

Each element acts as a small capacitance. As lightfalls on a pixel, it liberates electrons, which effec-tively charge the capacitance. The number of elec-trons stored is then proportional to the intensity orbrightness of the light received. The charge in eachpixel can be read out by applying a small voltageacross the chip.

The CCD is most sensitive to red light, but the STISchip has been enhanced through a “backside treat-ment” to provide a usable sensitivity in the near-UV.It is sensitive from approximately 200 nm to thenear-infrared at 1000 nm.

The CCD can make exposures ranging from 0.1 second to 60 minutes. In space, above Earth’sprotective atmosphere, radiation from cosmic raysis higher than at Earth’s surface. CCDs are sensitiveto cosmic rays, which can produce large numbers ofelectrons in the pixels. For this reason, two shorterexposures of up to 1 hour are made. Comparison ofthe frames allows cosmic ray effects to besubtracted.

Imaging Operational Modes. STIS can be used toacquire an image of an object in UV or visible light.To do this, an open aperture is selected and a mirrorplaced in the beam by the MSM. The instrument hasnine filters that can be selected. The cameras for theCCD and the MAMAs have different magnificationfactors. The FOV is 25 x 25 arcsec for the MAMAsand 50 x 50 arcsec for the CCD.

Target Acquisition. Normally an object is acquiredusing the CCD camera with a 50 x 50-arcsec field.Two short exposures are taken to enable subtraction

of cosmic rays. The HST FGSs have a pointing accu-racy of ±2 arcsec, and the target usually is easilyidentifiable in the field. Once identified, an object ispositioned via small angle maneuvers to the center ofthe chosen science mode slit position. Two moreexposures are made, the calibration lamp is flashedthrough the slit to confirm the exact slit position anda further peak up on the image is performed.Acquisition can take up to 20 minutes.

Data Acquisition. The MAMAs take data in thehigh-resolution mode. For normal imaging and spec-troscopy, the data is integrated in the onboardcomputer and stored in this format on the solid-staterecorders for later downlink. The MAMAs also have atime-tag mode, where each photon is stored individu-ally with its arrival time and location (x, y, t). The datainitially is stored in a 16-megabyte memory, thendownloaded into the onboard recorder. The time-tagmode has a time resolution of 125 microseconds.

STIS Specifications

Fig. 4-13 shows STIS specifications.

Observations

Scientists use STIS in many areas:• Searching for massive black holes by studying star

and gas dynamics around the centers of galaxies• Measuring the distribution of matter in the

universe by studying quasar absorption lines• Watching stars forming in distant galaxies • Mapping fine details of planets, nebulae, galaxies

and other objects• Imaging Jupiter-sized planets around nearby stars• Obtaining physical diagnostics, such as chemical

composition, temperature, density and velocity ofrotation or internal mass motions in planets,comets, stars, interstellar gas, nebulae, stellarejecta, galaxies and quasars.

Weight 825 pounds (374 kg)Dimensions 3 x 3 x 7 feet (0.9 x 0.9 x 2.2 m)Principal investigator Dr. Bruce E. Woodgate, GSFCPrime contractor Ball AerospaceField of view MAMA 24.9 x 24.9 arcsec

CCD 51 x 51 arcsecPixel format 1024 x 1024Wavelength range 115 – 1000 nanometers

Space Telescope Imaging Spectrograph (STIS)

Fig. 4-13 STIS specificationsK1175_416

SCIENCE INSTRUMENTS

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Wide Field and PlanetaryCamera 2

Hubble’s “workhorse” camera isWFPC2. It records two-dimen-sional images at two magnifica-tions through a selection of 48color filters covering a spectralrange from far-UV to visible andnear-IR wavelengths. It providespictorial views of the celestialuniverse on a grander scale thanany other instrument flown to date.

Like its predecessor WFPC1,WFPC2 was designed and built atNASA’s Jet Propulsion Laboratory(JPL), which is operated by theCalifornia Institute of Technology.Professor James A. Westphal ofCaltech was the principal investi-gator for WFPC1. Dr. John T.Trauger of JPL is the principalinvestigator for WFPC2.

WFPC1, the first-generationinstrument, was launched withthe Telescope in 1990 and func-tioned flawlessly. WFPC2, thesecond-generation instrument,was already under constructionwhen Hubble was launched. Itsoriginal purpose was to provide abackup for WFPC1 with certainenhancements, including anupgraded set of filters, advanceddetectors and improved UVperformance. With modificationsintroduced after 1990, WFPC2also provided built-in compensa-tion for the improper curvature of the Telescope’s primarymirror. WFPC2 has four CCDcameras arranged to record simul-taneous images in four separateFOVs at two magnifications.

In three WFC fields, each detectorpixel occupies 0.1 arcsec and eachdetector array covers a square 800 pixels on a side—80 arcsec,slightly more than the diameter ofJupiter when it is nearest theEarth. The Telescope is designed to

concentrate 70 percent of the lightof a star image into a circle 0.2 arcsec(two WFC pixels) in diameter.Operating at a focal ratio of f/12.9,this three-field camera provides thegreatest sensitivity for the detec-tion of faint objects. Stars as faintas 29th magnitude are detectable inthe longest exposures (29th magni-tude is more than 1 billion timesfainter than can be seen with thenaked eye).

The Planetary Camera provides amagnification about 2.2 timeslarger: each pixel occupies only0.046 arcsec and the single squareFOV is only 36.8 arcsec on a side.It operates at a focal ratio off/28.3. Originally incorporated forstudying the finest details ofbright planets, the PlanetaryCamera actually provides theoptimum sampling of theTelescope’s images at visible wave-lengths. Brightness permitting,this camera is used whenever thefinest possible spatial resolution isneeded, even for stars, stellarsystems, gaseous nebulas andgalaxies.

With its two magnifications andbuilt-in correction for theTelescope’s spherical aberration,WFPC2 can resolve the fine detailsand pick out bright stellar popula-tions of distant galaxies. It canprecisely measure the brightness offaint stars and study the character-istics of stellar sources even incrowded areas such as globularclusters—ancient swarms of asmany as several hundred thousandstars that reside within a hugespherical halo surrounding theMilky Way and other galaxies.WFPC2’s high-resolution imageryof the planets in Earth’s solarsystem allows continued studies oftheir atmospheric composition aswell as discovery and study oftime-varying processes on theirsurfaces.


WFPC2 occupies one of four radialbays in HST’s focal plane struc-ture. (The other three radial bayssupport the FGSs, used primarilyto control pointing of theTelescope.) WFPC2’s FOV islocated at the center of theTelescope’s FOV, where the tele-scopic images are nearly on axisand least affected by residual aber-rations (field curvature and astig-matism) inherent in the Ritchey-Chretien design.

Because other instruments sharethe focal plane, WFPC2 is equippedwith a flat pick-off mirror locatedabout 18 inches ahead of the focalplane and tipped at almost 45 degreesto the axis of the Telescope. Thepick-off mirror is attached to theend of a stiff truss, which is rigidlyfastened to WFPC2’s preciselylocated optical bench. The pick-offmirror reflects the portion of theTelescope’s focal plane belonging toWFPC2 into a nearly radial direc-tion. From there it enters the frontof the instrument, allowing lightfalling on other portions of thefocal plane to proceed without interference.

Figure 4-14 shows the overallconfiguration of WFPC2. It isshaped somewhat like a piece ofpie, with the pick-off mirror lyingat the point of the wedge and alarge, white-painted cylindricalpanel 2.6 feet (0.8 m) high and 7feet (2.2 m) wide at the other end.The panel forms part of the curvedouter skin of the Support SystemsModule (SSM) and radiates awaythe heat generated by the cameras’electronics. WFPC2 is held in posi-tion by a system of latches and isclamped in place by a threadedfastener at the end of a long shaftthat penetrates the radiator and isaccessible to the astronauts.

WFPC2 weighs 619 pounds (281 kg).The cameras comprise fourcomplete optical subsystems, fourCCDs, four cooling systems usingthermoelectric heat pumps and adata-processing system to operatethe instrument and send data tothe Science Instrument Controland Data Handling (SI C&DH)subsystem.

Optical System. The WFPC2optical system consists of the pick-off mirror, an electrically operatedshutter, a selectable optical filterassembly and a four-facetedreflecting pyramid mirror used topartition the focal plane to the fourcameras. Light reflected by thepyramid faces is directed by four“fold” mirrors into four two-mirrorrelay cameras. The relays re-imagethe Telescope’s original focal planeonto the four detector arrays whileproviding accurate correction forthe spherical aberration of theprimary mirror. Figure 4-15 showsthe light path from the Telescope tothe detectors.

As in an ordinary camera, theshutter controls the exposure time,which can range from about 1/10thsecond to 28 hours. Typical exposuretime is 45 minutes, about the timerequired for the Telescope tocomplete half an orbit.

WFPC2’s pick-off mirror and threefold mirrors are equipped withactuators that allow them to becontrolled in two axes (tip andtilt) by remote control from theground. The actuators ensure thatthe spherical aberration correctionbuilt into WFPC2 is accuratelyaligned relative to the Telescope inall four channels.

The Selectable Optical FilterAssembly (SOFA) consists of 12independently rotatable wheels,each carrying four filters and oneclear opening (a total of 48 filters).These can be used singly or incertain pairs. Some of the WFPC2’sfilters have a patchwork of areaswith differing properties toprovide versatility in measuringspectral characteristics of sources.

WFPC2 also has a built-in cali-bration channel in which stable incandescent light sources serve as references for photometricobservations.

Charge-Coupled Detectors. ACCD is a device fabricated bymethods developed for the manu-facture of integrated electroniccircuits. Functionally, it consists ofan array of light-sensitive pixelsbuilt onto a thin wafer of crys-talline silicon. Complex electroniccircuits also built onto the wafercontrol the light-sensitive elements.The circuits include low-noiseamplifiers to strengthen signalsthat originate at the light sensors.As light falls on the array, photonsof light interact with the sensormaterial to create small electricalcharges (electrons) in the material.The charge is nearly proportionalto the number of photonsabsorbed. The built-in circuits readout the array, sending a successionof signals that will allow laterreconstruction of the pattern ofincoming light on the array.

SCIENCE INSTRUMENTS

4-12

Fig. 4-14 Wide Field and Planetary Camera (WFPC)overall configuration

Radiator

Light Seal

ShutterUV Fold Mirror

Guiderail

-V3

+V1

-V2

+V3

+V2

HeatPipes

PurgeGas Line

RegistrationFittingPoint A

RelayOpticsAssembly

Pick-offMirrorCoverHinge Lug

RadiatorSupport Struts

Pick-off MirrorMechanism

CameraHead

EVAHandrail

Optical Bench(Graphite Epoxy)

Filter Selector(40 Filters)

MultilayerInsulation

ArticulatingFold Mirrors

CalibrationModule

Optical BenchSupport Struts

RegistrationFitting Point B

ElectronicsCompartment

TestConnector

Radiator/Bay 5Support Struts

EntranceAperture

1/2 Pick-offMirror

MultilayerInsulation

K1175_417

Light BaffleInvar Bulkhead

Pryamid (Fixed)

SCIENCE INSTRUMENTS

4-13

The CCDs used in WFPC2 consist of 800 rows and800 columns of pixels (640,000 pixels in each array).The pixels resemble tiny squares, 15 microns (about6/10,000 inch) on a side. Their sensitivity to light isgreatest at near-IR and visible wavelengths. InWFPC2 the pixels are coated with a thin fluorescentlayer that converts UV photons to visible ones.

To achieve a very low noise background that doesnot interfere with measurements of faint astronom-ical light sources, the CCDs must be operated at alow temperature, approximately -50 to -70°C (-8 to -130°F). An electrically operated solid-state coolingsystem pumps heat from the cold CCDs to thewarmer external radiator by means of heat pipes.The radiator faces away from the Earth and Sun sothat its heat can be radiated into the cold vacuumof space.

CCDs are much more sensitive to light thanphotographic film and many older forms ofelectronic light sensors. They also have finerresolution, better linearity and the ability toconvert image data directly into digital form.As a result, CCDs have found many astro-nomical and commercial applications follow-ing their early incorporation in WFPC1.

Processing System. A microprocessorcontrols all of WFPC2’s operations and

transfers data to the SI C&DH unit. Commands tocontrol various functions of the instrument(including filter and shutter settings) are sent byradio uplink to the Telescope in the form of detailedencoded instructions that originated at the SpaceTelescope Science Institute (STScI) in Baltimore,Maryland. Because the information rate of theTelescope’s communication system is limited, thelarge amount of data associated with even onepicture from WFPC2 is digitally recorded during theCCD readout. The data then is transmitted at aslower rate via a communications satellite that issimultaneously in Earth orbit.

WFPC2 Specifications

Figure 4-16 shows the WFPC2 specifications.

Pyramid

Heat Pipe

Pyramid

Shutter

ExternalRadiator

RadiationShielding

Pick-offMirror

PlanoRelay Mirror

Ritchey-ChretienRepeater

Charge-CoupledDetector Assembly

Charge-CoupledDetector AlignmentBands

OpticalTelescopeAssemblyOptical Axis

SensorElectronicsPlatform

K1175_418Fig. 4-15 WFPC optics design


Dimensions Camera: 3.3 x 5 x 1.7 feet (1 x 1.3 x 0.5 m)

Radiator: 2.6 x 7 feet (0.8 x 2.2 m)

Principal investigator John Trauger, Jet Propulsion Laboratory

Contractor Jet Propulsion Laboratory

Optical modes f/12.9 (WF), f/28.3 (PC)

Field of view 4.7 arcmin2 (WP)

0.3 arcmin2 (PC)

Magnitude range 9 to 28 mv

Wavelength range 1200 – 10,000 angstroms

Wide Field and Planetary Camera 2

Fig. 4-16 WFPC2 specifications K1175_419

SCIENCE INSTRUMENTS

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Observations

The WFPC2 can perform several tasks whileobserving a single object. It can focus on an extendedgalaxy and take a wide-field picture of the galaxy,then concentrate on the galaxy nucleus to measurelight intensity and take photographic closeups of thecenter. In addition, the WFPC2 can measure whileother instruments are observing.

Specific applications of this camera range from testsof cosmic distance scales and universe expansiontheories to specific star, supernova, comet and planetstudies. Important searches are being made for blackholes, planets in other star systems, atmosphericstorms on Mars and the connection between galaxy collisions and star formation.

Astrometry (Fine Guidance Sensors)

When two FGSs lock on guide stars to providepointing information for the Telescope, the third FGSserves as a science instrument to measure the posi-tion of stars in relation to other stars. This astrom-etry helps astronomers determine stellar masses anddistances.

Fabricated by Perkin Elmer, the sensors are in thefocal plane structure, at right angles to the opticalpath of the Telescope and 90 degrees apart. As shownin Fig. 4-17, they have pick-off mirrors to deflectincoming light into their apertures. (See page 5-20 for details.)

Each refurbished FGS has been upgraded by the addition of an adjustable fold mirror (AFM). This

device allows HST’s optical beam to be properlyaligned to the internal optics of the FGS by groundcommand. The first-generation FGSs did not containthis feature and their optical performance sufferedas a consequence. During SM2 astronauts removed FGS 1 from HST and replaced it with FGS 1R, thefirst FGS to feature this active alignment capability.Now with its optical system properly aligned, FGS IRperforms superbly and is the prime instrument onHST for astrometric science observations.

Fine Guidance Sensor Specifications

Figure 4-18 shows FGS specifications.

Operational Modes for Astrometry

Astrometric observations of binary stars provide in-formation about stellar masses that is important tounderstanding the evolution of stars. Once the twotarget-acquisition FGSs lock onto guide stars, thethird sensor can perform astrometric operations ontargets within the FOV set by the guide stars’ posi-tions. The sensor should be able to measure stars as faint as 18 apparent visual magnitude.

There are three operational modes for astrometricobservations: • Position • Transfer-function• Moving-target.

Position mode allows the astrometric FGSs to calculate the angular position of a star relative to theguide stars. Generally, up to 10 stars will be measuredwithin a 20-minute span.

In the transfer-function mode, sensors measure the angular size of a target, either through directanalysis of a single-point object or by scanning anFig. 4-17 Fine Guidance Sensor (FGS)

K1175_420

Enclosure

Filter (5)

Pick-off Mirror

Optical Bench

Pinhole/LensAssembly (4)

CorrectorGroupDeviationPrism

DoubletLens (4)

Koesters’Prisms

AsphericCollimatingMirror

Star SelectorMirrors


Dimensions 1.6 x 3.3 x 5.4 feet (0.5 x 1 x 1.6 m)

Contractor Perkin Elmer

Astrometric modes Stationary and moving target, scan

Precision 0.002 arcsec2

Measurement speed 10 stars in 10 minutes

Field of view Access: 60 arcmin2

Detect: 5 arcsec

Magnitude range 4 to 18.5 mv

Wavelength range 4670 – 7000 angstroms

Fine Guidance Sensor

Fig. 4-18 FGS specificationsK1175_421

SCIENCE INSTRUMENTS

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extended target. Examples of the latter include solarsystem planets, double stars and targets surroundedby nebulous gases.

In moving-target mode, sensors measure a rapidlymoving target relative to other targets when it isimpossible to precisely lock onto the moving target,for example, measuring the angular position of amoon relative to its parent planet.

Fine Guidance Sensor Filter Wheel

Each FGS has a filter wheel for astrometric measure-ment of stars with different brightness and to clas-sify the stars being observed. The wheel has a clearfilter for guide-star acquisition and faint-star (greaterthan 13 apparent visual magnitude) astrometry. Aneutral-density filter is used for observation ofnearby bright stars. Two colored filters are used toestimate a target’s color (chemical) index, increasingcontrast between close stars of different colors orreducing background light from star nebulosity.

Astrometric Observations

Astronomers measure the distance to a star bycharting its location on two sightings from Earth atdifferent times, normally 6 months apart. The Earth’sorbit changes the perceived (apparent) location of thenearby star and the parallax angle between the twolocations can lead to an estimate of the star’sdistance. Because stars are so distant, the parallaxangle is very small, requiring a precise FOV to calcu-late the angle. Even with the precision of the FGSs,astronomers cannot measure distances by theparallax method beyond nearby stars in the MilkyWay galaxy.

An important goal of the FGS astrometry project is to obtain improved distances to fundamentaldistance calibrators in the universe, for instance, tothe Hyades star cluster. This is one of the founda-tions of the entire astronomical distance scale.Knowing the accurate distance to the Hyades wouldmake it possible for astronomers to infer accuratedistances to similar stars that are too distant for the direct parallax method to work.

Astronomers have long suspected that some starsmight have a planetary system like that around theSun. Unfortunately, the great distance of stars andthe faintness of any possible planet make it verydifficult to detect such systems directly. It may bepossible to detect a planet by observing nearby starsand looking for the subtle gravitational effects that a planet would have on the star it is orbiting.

Astronomers use the FGS in two modes of operationto investigate known and suspected binary starsystems. Their observations lead to the determina-tion of the orbits and parallaxes of the binary starsand therefore to the masses of these systems. Forexample, 40 stars in the Hyades cluster wereobserved with the FGS. Ten of the targets werediscovered to be binary star systems and one ofthem has an orbital period of 3.5 years.

Other objects, such as nearby M dwarf stars withsuspected low-mass companions, are being investi-gated with the FGS with the hope of improving themass/luminosity relationship at the lower end of the main sequence.

he Hubble Space Telescope(HST) performs much like aground astronomical obser-

vatory. It has three interactingsystems:• Support Systems Module

(SSM), an outer structure thathouses the other systems andprovides services such as elec-trical power, data communica-tions, pointing control andmaneuvering.

• Optical Telescope Assembly(OTA), which collects andconcentrates incoming light inthe focal plane for use by thescience instruments.

• Eight major science instru-ments, four housed in an aftsection focal plane structure(FPS) and four placed along thecircumference of the spacecraft.The Science Instrument

Control and Data Handling (SI C&DH) unit controls all theinstruments except the FineGuidance Sensors (FGS).

The SSM communicates with theOTA, SI C&DH unit and instru-ments to ready an observation.Light from an observed targetpasses through the Telescope andinto one or more of the scienceinstruments, where the light isrecorded. This information goesto onboard computers forprocessing, then it is eithertemporarily stored or sent toEarth in real time, via the space-craft communication system.

Two Solar Arrays (SA) alsosupport HST operations. Theygenerate electrical power andcharge onboard batteries and

communications antennas toreceive commands and sendtelemetry data from the HST.

Figure 5-1 shows the HST configuration.

The Telescope completes oneorbit every 97 minutes and main-tains its orbital position alongthree axial planes. The primaryaxis, V1, runs through the centerof the Telescope. The other twoaxes parallel the SA masts (V2)and the High Gain Antenna(HGA) masts (V3) (see Fig. 5-2).The Telescope points and maneu-vers to new targets by rotatingabout its body axes. Pointinginstruments use references tothese axes to aim at a target inspace, position the SA or changeTelescope orientation in orbit.

HST SYSTEMS

T

5-1

HST SYSTEMS

5-2

Support Systems Module

Design features of the SSM include:• An outer structure of interlocking shells• Reaction wheels and magnetic torquers to maneuver,

orient and attitude stabilize the Telescope

• Two SAs to generate electrical power• Communication antennas• A ring of Equipment Section bays that contain elec-

tronic components, such as batteries, and communi-cations equipment. (Additional bays are provided onthe +V3 side of the spacecraft to house OTA elec-tronics as described on page 5-19, OTA EquipmentSection.)

• Computers to operate the spacecraft systems andhandle data

• Reflective surfaces and heaters for thermal protection• Outer doors, latches, handrails and footholds designed

for astronaut use during on-orbit maintenance.

Figure 5-3 shows some of these features.

Major component subsystems of the SSM are:• Structures and mechanisms• Instrumentation and communications• Data management• Pointing control• Electrical power• Thermal control• Safing (contingency) system.

Fig. 5-1 Hubble Space Telescope – exploded view

Fig. 5-2 Hubble Space Telescope axes

Magnetic Torquer (4)High Gain Antenna (2)

Main BaffleSolar Array (2)

Light Shield

K1175_501

Aperture DoorSupport Systems Module Forward Shell

Secondary Mirror Baffle

Central Baffle

Optical Telescope AssemblySecondary Mirror Assembly

Optical Telescope AssemblyPrimary Mirror and Main Ring

Fine Guidance Optical Control Sensor (3)

Optical Telescope Assembly Focal Plane Structure

Support Systems Module Aft Shroud

Fixed Head Star Tracker (3) and Rate Sensor Unit (3)

Radial Science Instrument Module (1)

Optical Telescope Assembly Equipment Section

Support Systems Module Equipment Section

Optical Telescope Assembly Metering Truss

Axial ScienceInstrumentModule (4)

+V3

+V1

+V2

-V3

+V2 -V1

+V3

-V2

Solar Array

K1175_502

HST SYSTEMS

Structures and Mechanisms Subsystem

The outer structure of the SSM consists of stackedcylinders, with the aperture door on top and theaft bulkhead at the bottom. Fitting together arethe light shield, the forward shell, the SSMEquipment Section and the aft shroud/bulkhead—all designed and built by Lockheed Martin SpaceSystems Company (see Fig. 5-4).

Aperture Door. A door approximately 10 feet (3 m) in diameter covers the opening to theTelescope’s light shield. The door is made fromhoneycombed aluminum sheets. The outside iscovered with solar-reflecting material, and theinside is painted black to absorb stray light.

The door opens a maximum of 105 degrees fromthe closed position. The Telescope aperture allowsfor a 50-degree field of view (FOV) centered on the+V1 axis. Sun-avoidance sensors provide amplewarning to automatically close the door beforesunlight can damage the Telescope’s optics. Thedoor begins closing when the Sun is within ±35degrees of the +V1 axis and is closed by the time thesun reaches 20 degrees of +V1. This takes no longerthan 60 seconds.

The Space Telescope Operations Control Center(STOCC) can override the protective door-closingmechanism for observations that fall within the 20-

degree limit. An example is observing a bright object,using the dark limb (edge) of the Moon to partiallyblock the light.

Light Shield. Used to block out stray light, the lightshield (see Figs. 5-4 and 5-5) connects to both theaperture door and the forward shell. The outer skinof the Telescope has latches to secure the SAs and

Fig. 5-4 Structural components of Support Systems Module

Fig. 5-3 Design features of Support Systems Module

High Gain Antenna

Crew HandrailsEquipment Bay

Computer

Digital Interface Unit

Reaction Wheel Assembly

Communication System

Sun Sensor (3)

Aft Shroud

Access Door

Solar Array

Light Shield

K1175_503

Low GainAntenna

UmbilicalInterface

ApertureDoor

ForwardShell

Batteries and Charge Controller

EquipmentSection

MagneticTorquers

Latch PinAssembly

Forward Shell

Aft Shroud


K1175_504

ApertureDoor

LightShieldMagnetic

Torquer (4)

EquipmentSection

5-3

HGAs when they are stowed.Near the SA latches are scuffplates—large protective metalplates on struts that extendapproximately 30 inches from thesurface of the spacecraft.Trunnions lock the Telescope intothe Shuttle cargo bay by hookingto latches in the bay. The lightshield supports the forward LowGain Antenna (LGA) and itscommunications waveguide, twomagnetometers and two sunsensors. Handrails encircle thelight shield, and built-in footrestraints support the astronautsworking on the Telescope.

The shield measures 13 feet (4 m)long and 10 feet (3 m) in internaldiameter. It is a stiffened, corru-gated-skin barrel machined frommagnesium and covered by athermal blanket. Internally theshield has 10 light baffles, paintedflat black to suppress stray light.

Forward Shell. The forwardshell, or central section of thestructure, houses the OTA mainbaffle and the secondary mirror(see Fig. 5-6). When stowed, theSAs and HGAs are latched flat

against the forward shell andlight shield. Four magnetictorquers are placed 90 degreesapart around the circumferenceof the forward shell. The outerskin has two grapple fixturesnext to the HGA drives, wherethe Shuttle’s RemoteManipulator System can attachto the Telescope. The forwardshell also has handholds,footholds and a trunnion, whichis used to lock the Telescope intothe Shuttle cargo bay.

Machined from aluminumplating, the forward shell is 13feet (4 m) long and 10 feet (3 m)in diameter. It has internal stiff-ened panels and external rein-forcing rings. These rings are onthe outside to ensure clearancefor the OTA inside. Thermalblankets cover the exterior.

Equipment Section. This sectionis a ring of storage bays encirclingthe SSM. It contains about 90percent of the electronic compo-nents that run the spacecraft,including equipment servicedduring extravehicular activities(EVA) by Space Shuttle astronauts.

The Equipment Section is adoughnut-shaped barrel that fitsbetween the forward shell andaft shroud. It contains 10 baysfor equipment and two bays tosupport aft trunnion pins andscuff plates. As shown in Fig. 5-7,clockwise from the +V3 (top)position, the bays contain:1. Bay 8 – pointing control

hardware2. Bay 9 – Reaction Wheel

Assembly (RWA)3. Bay 10 – SI C&DH unit4. Unnumbered trunnion

support bay5. Bay 1 – data management

hardware

HST SYSTEMS

5-4

Fig. 5-5 Aperture door and light shield

Fig. 5-6 Support Systems Module forward shell

Aperture Door

Light Shield

Solar Array Latches

K1175_505

Aperture Door Hinge Support

Integrally Stiffened Skin

Internal Baffle Rings

Aperture Door Hinge

High Gain Antenna Latches

High Gain Antennaand Solar ArrayLatch Support Ring

MagnesiumMonocoqueSkin

Light ShieldAssembly/Forward ShellAttach Ring

Crew Aids

K1175_506

High GainAntenna Mast

MagneticTorquers

Stowed Solar Arrays

IntegrallyStiffenedSkin Panels

Equipment Section/Forward ShellInterface Ring

Forward ShellReinforcingRings

StowedHigh GainAntennas

6. Bays 2, 3 and 4 – electricalpower equipment

7. Unnumbered trunnionsupport bay

8. Bay 5 – communicationhardware

9. Bay 6 – RWA10.Bay 7 – mechanism

control hardware.

The cross section of the baysis shaped like a trapezoid: theouter diameter (the door) is3.6 feet (1 m) and the innerdiameter is 2.6 feet (0.78 m).The bays are 4 feet (1.2 m)wide and 5 feet (1.5 m) deep.The Equipment Section isconstructed of machined andstiffened aluminum framepanels attached to an inneraluminum barrel. Eight bayshave flat, honeycombedaluminum doors mountedwith equipment. In Bays 6and 9, thermal-stiffened paneldoors cover the reactionwheels. A forward framepanel and aft bulkhead enclosethe SSM Equipment Section.Six mounts on the inside ofthe bulkhead hold the OTA.

Aft Shroud and Bulkhead.The aft shroud (see Fig. 5-8)houses the FPS containingthe axial science instru-ments. It is also the loca-tion of the CorrectiveOptics Space TelescopeAxial Replacement(COSTAR) unit.

The three FGSs and theWide Field and PlanetaryCamera 2 (WFPC2) arehoused radially near theconnecting point betweenthe aft shroud and SSMEquipment Section. Doorson the outside of the shroudallow astronauts to remove andchange equipment and instru-ments easily. Handrails and footrestraints for the crew run alongthe length and circumference ofthe shroud. During maintenanceor removal of an instrument,

interior lights illuminate thecompartments containing thescience instruments. The shroudis made of aluminum, with astiffened skin, internal panelsand reinforcing rings, and 16external and internal longeronbars for support. It is 11.5 feet

(3.5 m) long and 14 feet (4.3 m)in diameter.

The aft bulkhead contains theumbilical connections betweenthe Telescope and the Shuttle,used during on-orbit mainte-nance. The rear LGA attaches

HST SYSTEMS

5-5

Fig. 5-7 Support Systems ModuleEquipment Section bays and contents

K1175_507

to the bulkhead, which is madeof 2-in.-thick honeycombedaluminum panels and has threeradial aluminum support beams.

The shroud and bulkheadsupport a gas purge system thatwas used to prevent contamina-tion of the science instrumentsbefore launch. All vents used toexpel gases are light tight toprevent stray light from enteringthe OTA focal plane.

Mechanisms. Along the SSMstructure are mechanisms thatperform various functions,including:• Latches to hold antennas and SAs• Hinge drives to open the aper-

ture door and erect arrays andantennas

• Gimbals to move the HGAdishes

• Motors to power the hingesand latches and to rotate arraysand antennas.

There are nine latches: four forantennas, four for arrays and onefor the aperture door. They latchand release using four-bar link-ages. Stepper motors calledRotary Drive Actuators (RDA)drive the latches.

There are three hinge drives,one for each HGA and one forthe door. The hinges also use anRDA. Both hinges and latcheshave hex-wrench fittings so anastronaut can manually operatethe mechanism to deploy thedoor, antenna or array if amotor fails.

Instrumentation andCommunications Subsystem

This subsystem provides thecommunications loop betweenthe Telescope and the Trackingand Data Relay Satellites(TDRS), receiving commandsand sending data through theHGAs and LGAs. All informa-tion passes through the DataManagement Subsystem(DMS).

S-Band Single AccessTransmitter (SSAT). HST isequipped with two SSATs. “S-band” identifies the frequencyat which the science data istransmitted and “single access”specifies the type of antenna onthe TDRS satellite to which thedata is sent.

High Gain Antennas. Each HGA

is a parabolic reflector (dish)mounted on a mast with a two-axis gimbal mechanism and elec-tronics to rotate it 100 degrees ineither direction (see Fig. 5-9).General Electric designed andmanufactured the antenna dishesusing honeycomb aluminum andgraphite-epoxy facesheets.

The HGAs achieve a much higherRF signal gain than the LGAs.The higher signal gain is required,for example, when transmittinghigh-data-rate scientific data.Because of their characteristicallynarrow beam widths, the HGAsmust be pointed at the TDRSs.Each antenna can be aimed with a1-degree pointing accuracy. Thisaccuracy is consistent with theoverall antenna beam width ofover 4 degrees. The antennas

transmit over two frequencies:2255.5 MHz or 2287.5 MHz (plusor minus 10 MHz).

Low Gain Antennas. The LGAsare spiral cones, manufactured byLockheed Martin, that providespherical coverage (omnidirec-tional). They are set 180 degreesapart on the light shield and aftbulkhead of the spacecraft.

HST SYSTEMS

5-6

Fig. 5-8 Support Systems Module aft shroud and bulkhead

Fig. 5-9 High Gain Antenna

Vents

+V3

+V2 +V1

Radial Science Instrument Doors

Axial Science Instrument Doors

Flight Support System Pin

Honeycomb Laminate Panels

Low Gain Antenna

Reinforcing Rings

Crew Aids

K1175_508

ElectricalUmbilicals

Flight Support SystemPin Support Beam

Integrally StiffenedSkin Panels

Equipment Section/Aft Shroud InterfaceRing

K1175_509

Twin-AxisGimbals

High GainAntenna

Operating over a frequency range from 2100 MHzto 2300 MHz, the LGAs receive ground commandsand transmit engineering data. These antennas areused for all commanding of the Telescope and forlow-data-rate telemetry, particularly duringTelescope deployment or retrieval on orbit andduring safemode operations.

Data Management Subsystem

The DMS receives communications commands fromthe STOCC and data from the SSM systems, OTAand science instruments. It processes, stores andsends the information as requested (see Fig. 5-10).

Subsystem components are:• Advanced Computer • Data Management Unit (DMU)• Four Data Interface Units (DIU)• Three engineering/science data recorders • Two oscillators (clocks).

The components are located in the SSM EquipmentSection, except for one DIU stored in the OTAEquipment Section.

The DMS receives, processes, and transmits fivetypes of signals:1. Ground commands sent to the HST systems2. Onboard computer-generated or computer-stored

commands

3. Scientific data from the SI C&DH unit4. Telescope engineering status data for telemetry5. System outputs, such as clock signals and

safemode signals.

Advanced Computer. The Advanced Computer is ageneral-purpose digital computer for onboard engi-neering computations. It executes stored commands,formats status data (telemetry), generates onboardcommands to orient the SAs toward the Sun, evalu-ates the health status of the Telescope systems andcommands the HGAs. It also performs all PointingControl Subsystem (PCS) computations tomaneuver, point and attitude stabilize the Telescope.

Based on the Intel 80486 microchip, the AdvancedComputer operates 20 times faster and has six timesas much memory as the DF-224 computer, which itreplaced on SM3A. It is configured as three inde-pendent single-board computers (SBC). Each SBChas 2 megabytes of fast static random accessmemory and 1 megabyte of non-volatile memory.

The Advanced Computer communicates with theHST by using the direct memory access capabilityon each SBC through the DMU. Only one SBCcontrols the Telescope at a time. The other SBCs canbe off, in an idle state or performing internal tasks.

Upon power on, each SBC runs a built-in self-testand then copies the operating software from slower

HST SYSTEMS

5-7

Fig. 5-10 Data Management Subsystem functional block diagram

Solar Array

AdvancedComputer

Command, Data Clock

Data, Clock, Mode Control

Keep-Alives

Reg Power

Data

Data

ScienceDataCommands

To/From Other Telescope Subsystems

K1175_510

Low GainAntennas

MultipleAccessTransponder

Pointing andSafemodeElectronicsAssembly

Rate GyroAssemblyElectronicsControl Unit

Electrical PowerTemperatureControlElectronics

Control Unit/Science DataFormatter

OvenControlledCrystalOscillator

Wide Field/PlanetaryCamera

MechanismControlUnit

OpticalControlElectronics

ActuatorControlElectronics

FineGuidanceElectronics

Fixed-HeadStar Tracker

DataInterface Unit

(Science InstrumentControl and DataHandling Unit)

Internal SystemControl Signals

Request, Replay, Clock,Synchronizing Pulses

DataManagementUnit

Solar ArrayTransmitter

Discrete SpecialSerial Commands

Support SystemsModule

Optical TelescopeAssembly

Data InterfaceUnits

Data, Status,Mode Control

DataRecorders

High GainAntennas

Functional Unit

Functional Redundancy

Interface Connection

Reference Equipment

Key

HST SYSTEMS

5-8

non-volatile memory to faster random access memory. The self-test can diagnose any problems with theAdvanced Computer and report them to the ground. The Advanced Computer uses fast static random accessmemory to eliminate wait states and allow it to run at its full-rated speed.

The Advanced Computer measures 18.8 x 18 x 13inches (0.48 x 0.46 x 0.33 m) and weighs 70.5 pounds(32 kg). It is located in Bay 1 of the SSM EquipmentSection (see Fig. 5-11).

Data Management Unit. The DMU links with thecomputer. It encodes data and sends messages toselected Telescope units and all DMS units, powersthe oscillators and serves as the central timing source.The DMU also receives and decodes all incomingcommands, then transmits each processed commandto be executed.

In addition, the DMU receives science data from theSI C&DH unit. Engineering data, consisting of sensorand hardware status readings (such as temperature orvoltages), comes from each Telescope subsystem. Thedata can be stored in the onboard data recorders ifdirect telemetry via a TDRS is unavailable.

The DMU is an assembly of printed-circuit boards,interconnected through a backplate and externalconnectors and attached to the door of Equipment Section Bay 1 (see Fig. 5-12). The unit weighs 83 pounds(37.7 kg) and measures 26 x 30 x 7 inches (60 x 70 x 17 cm).

Data Interface Unit. Four DIUs provide a command and data link between the DMS and other electronicboxes. The DIUs receive commands and data requests from the DMU and pass data or status information backto the DMU. The OTA DIU is located in the OTA Equipment Section; the other units are in Bays 3, 7 and 10 ofthe SSM Equipment Section. As a safeguard, each DIUis two complete units in one: either part can handlethe unit’s functions. Each DIU measures 15 x 16 x 7inches (38 x 41 x 18 cm) and weighs 35 lb (16 kg).

Engineering/Science Data Recorders. The DMSincludes three data recorders that store engineering orscience data that cannot be transmitted to the groundin real time. These recorders, located in EquipmentSection Bays 5 and 8, hold up to 12 billion bits ofinformation. Two solid state recorders (SSR) are usedin normal operations; the third, a backup, is a reel-to-reel tape recorder. Each recorder measures 12 x 9 x 7inches (30 x 23 x 18 cm) and weighs 20 pounds (9 kg).

The SSRs have no reels or tape and no moving partsto wear out and limit lifetime (their expected on-orbitlife is at least 8 years). Data is stored digitally incomputer-like memory chips until HST operators atGSFC command the SSR to play it back. Althoughthey are the same size as the reel-to-reel recorders,the SSRs can store over 10 times more data—12 giga-bits versus only 1.2 gigabits for the tape recordersthey replaced.

Fig. 5-11 Advanced computer

Fig. 5-12 Data Management Unit configuration

K1175_511

K1175_512

Top Cover(With Compression Pad)

Coax Connector

Bottom Cover

MatrixConnector

Card Guide

InterfaceConnector

Power Supply No. 2(CDI DC-DCConverter)

PC BoardStandard(5 x 7 in.)

HeatShieldPartition Enclosure

(Dip-BrazedAluminum)

Power SupplyNo. 1(DMU DC-DCConverter)

HST SYSTEMS

5-9

Each SSR can record two data streams simultane-ously, allowing both science and engineering data tobe captured on a single recorder. In addition, datacan be recorded and played back at the same time.

Oscillator. The oscillator provides a highly stablecentral timing pulse required by the Telescope. It hasa cylindrical housing 4 inches (10 cm) in diameterand 9 inches (23 cm) long and weighs 3 pounds (1.4kg). The oscillator and a backup are mounted in Bay2 of the SSM Equipment Section.

Pointing Control Subsystem

A unique PCS maintains Telescope pointing stabilityand aligns the spacecraft to point to and remainlocked on any target. The PCS is designed forpointing within 0.01 arcsec and holding theTelescope in that orientation with 0.007-arcsecstability for up to 24 hours while HST orbits theEarth at 17,500 mph. If the Telescope were in LosAngeles, it could hold a beam of light on a dime inSan Francisco without the beam straying from thecoin’s diameter.

Nominally, the PCS maintains the Telescope’s preci-sion attitude by locating guide stars in two FGSs andkeeping the Telescope in the same position relativeto these stars. When specific target requests requirerepositioning the spacecraft, the PCS selectsdifferent reference guide stars and moves theTelescope into a new attitude.

The PCS encompasses the Advanced Computer,various attitude sensors and two types of devices,called actuators, to move the spacecraft (see Fig. 5-13).It also includes the Pointing/Safemode ElectronicsAssembly (PSEA) and the Retrieval Mode GyroAssembly (RMGA), which are both used by thespacecraft safemode system. See page 5-13, Safing(Contingency) System, for details.

Sensors. The PCS uses five types of sensors: CoarseSun Sensors (CSS), Magnetic Sensing System (MSS),Rate Gyro Assemblies (RGA), Fixed Head StarTrackers (FHST) and FGSs.

Five CSSs, located on the light shield and aftshroud, measure the Telescope’s orientation to theSun. They also are used to calculate the initialdeployment orientation of the Telescope, determinewhen to begin closing the aperture door and pointthe Telescope in special Sun-orientation modesduring contingency operations. In addition, theCSSs provide signals to the PSEA, located in Bay 8of the SSM Equipment Section.

The MSS measures the Telescope’s orientation rela-tive to Earth’s magnetic field. Two systems arelocated on the front end of the light shield. Eachconsists of magnetometers and dedicated electronicunits that send data to the Advanced Computer andthe Safemode Electronics Assembly.

HST has three RGAs, each consisting of a RateSensor Unit (RSU) and an Electronics Control Unit(ECU). An RSU contains two rate-sensing gyro-scopes that measure attitude rate motion abouttheir sensitive axes. Two sets of dedicated elec-tronics in each ECU process this output. Three ofthe six gyroscopes are required to continue theTelescope science mission.

The RSUs are located behind the SSM EquipmentSection, next to three FHSTs in the aft shroud. TheECUs are located inside Bay 10 of the SSMEquipment Section. The RGAs provide input to thePCS to control the orientation of the Telescope’s lineof sight and to give the attitude reference whenmaneuvering the Telescope.

An FHST is an electro-optical detector that locatesand tracks a specific star within its FOV. STOCCuses FHSTs as an attitude calibration device whenthe Telescope maneuvers into its initial orientation.The trackers also calculate attitude informationbefore and after maneuvers to help the FGS lockonto guide stars.

Three FGSs provide angular position with respectto the stars (see page 5-20, Fine Guidance Sensor,for details). Their precise fine-pointing adjust-ments, accurate to within a fraction of anarcsecond, pinpoint the guide stars. Two of theFGSs perform guide-star pointing and the third isavailable for astrometry, the positional measure-ment of specific stars.

Pointing Control Subsystem Software. PCS soft-ware accounts for a large percentage of the flightcode executed by Hubble’s main computer. This soft-ware translates ground targeting commands intoreaction wheel torque profiles that reorient thespacecraft and smooth spacecraft motion to mini-mize jitter during data collection. The software alsodetermines Telescope orientation, or attitude, fromFHST or FGS data and commands the magnetictorquer bars to minimize reaction wheel speeds. Inaddition, the software provides various telemetryformats.

Since the Telescope was launched, the PCS has beenmodified significantly. A digital filtering scheme,

HST SYSTEMS

5-10

known as Solar Array Gain Augmentation (SAGA),now mitigates the effect of any SA vibration or jitteron pointing stability and an FGS Re-CenteringAlgorithm improves FGS performance when theTelescope is subjected to the same disturbances.

Software is used extensively to increase Telescoperobustness during hardware failures. Two additional

software safemodes have been provided. The spin-stabilized mode enables pointing of the Telescope -V1 axis to the Sun with only two of the four RWAsoperating. The other mode allows Sun pointing ofthe Telescope without any input from the RGA.Magnetometer and CSS data is used to derive allreference information needed to maintain Sunpointing (+V3 and -V1 are options).

Fig. 5-13 Location of Pointing Control Subsystem equipment

Fine GuidanceSensor (3)

Rate SensorUnit (3)

Coarse SunSensor (2)

Fixed HeadStar Tracker (3)

Science Instruments

Equipment Section

Computer

Reaction Wheel (4)

MagneticTorquer (4)

Magnetometer (2)Coarse Sun Sensor (2)

Bay 1 Data Management Computer

Bay 6 Reaction WheelReaction Wheel Assembly (2)No. 1 ForwardNo. 2 Aft

Bay 7 Mechanism Control

Bay 8 Pointing Control and InstrumentsRetrieval Mode Gyro AssemblyPointing and Safemode Electronics Assembly

Bay 9 Reaction Wheel (2)No. 3 ForwardNo. 4 Aft

Bay 10 ScienceInstrumentControl andData Handling

Looking ForwardK1175_513

-V2

-V3

+V2

+V3

10

9

87

6

5

4

3 2

1

HST SYSTEMS

5-11

A further software change “refreshes” the FGSconfiguration. Data is maintained in the AdvancedComputer memory so it can be sent periodically tothe FGS electronics, which are subject to single-eventupsets (logic state change) when transitioningthrough the South Atlantic Anomaly.

Actuators. The PCS has two types of actuators: RWAsand magnetic torquers. Actuators move the spacecraftinto commanded attitudes and provide control torquesto stabilize the Telescope’s line of sight.

The reaction wheels rotate a large flywheel up to3000 rpm or brake it to exchange momentum withthe spacecraft. Wheel assemblies are paired, twoeach in Bays 6 and 9 of the SSM Equipment Section.The wheel axes are oriented so that the Telescopecan provide science with only three wheels oper-ating. Each wheel measures 23 inches (59 cm) indiameter and weighs about 100 pounds (45 kg).Figure 5-14 shows the RWA configuration.

Magnetic torquers are primarily used to managereaction wheel speed. The torquers react againstEarth’s magnetic field. The torque reaction occurs inthe direction that reduces the reaction wheel speed,managing the angular momentum.

Located externally on the forward shell of the SSM,the magnetic torquers also provide backup control tostabilize the Telescope’s orbital attitude duringcontingency modes (refer to page 5-6, Instrumentationand Communications Subsystem. Each torquer is 8.3feet (2.5 m) long and 3 inches (8 cm) in circumferenceand weighs 100 lb (45 kg).

Pointing Control Operation. To point precisely, thePCS uses the gyroscopes, reaction wheels, magnetictorquers, star trackers and FGSs. The latter providethe precision reference point from which theTelescope can begin repositioning. Flight software

commands the reaction wheels to spin, acceleratingor decelerating as required to rotate the Telescopetoward a new target. Rate gyroscopes sense theTelescope’s angular motion and provide a short-termattitude reference to assist fine pointing and space-craft maneuvers. The magnetic torquers reduce reac-tion wheel speed.

As the Telescope nears the target area, star trackerslocate preselected reference stars that stand outbrightly in that region of the sky. Once the startrackers reduce the attitude error below 60 arcsec,the two FGSs take over the pointing duties. Workingwith the gyroscopes, the FGSs make it possible topoint the Telescope within 0.01 arcsec of the target.The PCS can maintain this position, wavering nomore than 0.005 arcsec, for up to 24 hours to guar-antee faint-object observation.

Electrical Power Subsystem

Power for the Telescope and science instrumentscomes from the Electrical Power Subsystem (EPS).The major components are two SA wings and theirelectronics, six batteries, six Charge CurrentControllers (CCC), one Power Control Unit (PCU)and four Power Distribution Units (PDU). All exceptthe SAs are located in the bays around the SSMEquipment Section.

During the servicing mission, the Shuttle will providethe electrical power. After deployment, the SAs willbegin converting solar radiation into electricity.Energy will be stored in nickel-hydrogen (NiH2)batteries and distributed by the PCUs and PDUs toall Telescope components as shown in Fig. 5-15.Hubble will not be released until the batteries arefully charged.

Solar Arrays. The SA panels, discussed later in thissection, are the primary source of electrical power.Each array wing has solar panels that convert theSun’s energy into electrical energy. Electricity producedby the panels charges the Telescope batteries.

Each array wing has associated electronics. Theseconsist of (1) a Solar Array Drive Electronics (SADE)unit to transmit positioning commands to the wingassembly, (2) a Deployment Control Electronics Unitto control the drive motors extending and retractingthe wings and (3) diode networks to direct the elec-trical current flow.

Batteries and Charge Current Controllers.Developed for the 1990 deployment mission, theTelescope’s batteries were NASA’s first flight NiH2

Fig. 5-14 Reaction Wheel Assembly

RWARWA

K1175_514

HST SYSTEMS

5-12

batteries. They provide the obser-vatory with a robust, long-lifeelectrical energy storage system.

Six NiH2 batteries support theTelescope’s electrical power needsduring three periods: whendemand exceeds SA capability,when the Telescope is in Earth’sshadow and during safemodeentry. The design, operation andhandling of the batteries—including special nondestructiveinspection of each cell—haveallowed them to be “astronaut-rated” for replacement during aservicing mission. To compensatefor the effects of battery aging,SM3A astronauts installed aVoltage/Temperature ImprovementKit (VIK) on each battery. TheVIK provides thermal stability byprecluding battery overchargewhen the HST enters safemode,effectively lowering the ChargeCurrent Controller (CCC)recharge current.

The batteries reside in SSMEquipment Section Bays 2 and 3.Each battery has 22 cells in seriesalong with heaters, heatercontrollers, pressure measurementtransducers and electronics, andtemperature-measuring devicesand their associated electronics.

Three batteries are packaged intoa module measuring roughly 36 x36 x 10 inches (90 x 90 x 25 cm)and weighing about 475 pounds(214 kg). Each module is equippedwith two large yellow handlesthat astronauts use to maneuverthe module in and out of theTelescope.

The SAs recharge the batteriesevery orbit following eclipse(the time in the Earth’sshadow). Each battery has itsown CCC that uses voltage-temperature measurements tocontrol battery recharge.

Fully charged, each batterycontains more than 75 amp-hours. This is sufficient energy tosustain the Telescope in normalscience operations mode for 7.5hours or five orbits. The batteriesprovide an adequate energyreserve for all possible safemodecontingencies and all enhance-ments programmed into theTelescope since launch.

Power Control and DistributionUnits. The PCU, to be replaced onSM3B, interconnects and switchescurrent flowing among the SAs,batteries and CCCs. Located inBay 4 of the Equipment Section,

the PCU provides the main powerbus to the four PDUs. The PCUweighs 120 pounds (55 kg) andmeasures 43 x 12 x 8 inches (109x 30 x 20 cm).

Four PDUs, located on the insideof the door to Bay 4, contain thepower buses, switches, fuses andmonitoring devices for electricalpower distribution to the rest ofthe Telescope. Two buses are dedi-cated to the OTA, science instru-ments and SI C&DH; two supplythe SSM. Each PDU measures 10 x5 x 18 inches (25 x 12.5 x 45 cm)and weighs 25 pounds (11 kg).

Thermal Control

Multilayer insulation (MLI)covers 80 percent of theTelescope’s exterior. The insula-tion blankets have 15 layers ofaluminized Kapton and an outerlayer of aluminized Teflon flex-ible optical solar reflector(FOSR). Aluminized or silveredflexible reflector tape covers mostof the remaining exterior. Thesecoverings protect against the coldof space and reflect solar heat.Supplemental electric heaters andreflective or absorptive paintsalso are used to keep Hubble’stemperatures safe.

Fig. 5-15 Electrical Power Subsystem functional block diagram

Solar A

rrayS

olar Array

Solar ArrayMechanisms

Power

Power

Power Power

Power

Power

Power

Power

Power

Power

Power

Power

Power

CommandsCommands

Commands

Commands

Solar ArrayElectronics

ControlAssembly

Telemetry

Telemetry

PowerControl

Unit

Battery No. 1

23

4

23

4

56

SSMSASIsOTA

SIC&DH

Telemetry

Orbiter Power(Predeployment)

PowerDistr

Unit 1

K1175_515

HST SYSTEMS

The SSM Thermal ControlSubsystem (TCS) maintainstemperatures within set limits forthe components mounted in theEquipment Section and structuresinterfacing with the OTA andscience instruments. The TCSmaintains safe component temper-atures even for worst-case condi-tions such as environmental fluc-tuations, passage from “cold” Earthshadow to “hot” solar exposureduring each orbit and heat gener-ated from equipment operation.

Specific thermal-protectionfeatures of the SSM include:• MLI thermal blankets for the

light shield and forward shell• Aluminum FOSR tape on the

aperture door surface facingthe Sun

• Specific patterns of FOSR andMLI blankets on the exteriorsof the Equipment Section baydoors, with internal MLI blan-kets on the bulkheads tomaintain thermal balancebetween bays

• Efficient placement of equip-ment and use of equipment bayspace to match temperaturerequirements, such as placingheat-dissipating equipment onthe side of the EquipmentSection mostly exposed to orbitshadow

• Silvered FOSR tape on the aftshroud and aft bulkhead exteriors

• Radiation blankets inside theaft shroud doors and MLI blan-kets on the aft bulkhead andshroud interiors to protect thescience instruments

• More than 200 temperaturesensors and thermistors placedthroughout the SSM, externallyand internally, to monitor indi-vidual components and controlheater operations.

Figure 5-16 shows the locationand type of thermal protectionused on the SSM.

During SM3A astronautsinstalled material to cover andrestore some degraded MLI. Thelayer added to the SSMEquipment Section on SM3A is acomposite-coated (siliconedioxide) stainless steel layer,known as the New Outer BlanketLayer (NOBL). The lightshield/forward shell material isTeflon with a scrim backing fordurability. The additional mate-rials have been life-tested to anequivalent of 10 years.

SM3B astronauts will completethe task of replacing thermalprotection in degraded areas astime permits.

Safing (Contingency) System

Overlapping or redundant equip-

ment safeguards the Telescopeagainst any breakdown. In addi-tion, a contingency or SafingSystem exists for emergencyoperations. Using dedicated PSEAhardware and many pointingcontrol and data managementcomponents, this system main-tains stable Telescope attitude,moves the SAs for maximum Sunexposure and conserves electricalpower by minimizing powerdrain. The Safing System canoperate the spacecraft indefi-nitely with no communicationslink to ground control.

During scientific observations(normal mode), the SafingSystem automatically monitorsTelescope onboard functions. Itsends Advanced Computer-gener-ated “keep-alive” signals to thePSEA that indicate all Telescopesystems are functioning. When afailure is detected, entry into theSafemode is autonomous.

The Safing System is designed tofollow a progression of contin-gency operating modes,depending on the situationaboard the Telescope. If amalfunction occurs and does notthreaten the Telescope’s survival,the Safing System moves into aSoftware Inertial Hold Mode.This mode holds the Telescope inthe last position commanded. If a

Fig. 5-16 Placement of thermal protection on Support Systems Module

BlackChemglaze

Aluminized Flexible Optical Solar Reflector (FOSR)

ApertureDoor

LightShield

ForwardShell

EquipmentSection Aft Shroud

90-degMultilayerInsulation(MLI)

90-deg MLI

+V1

AluminizedFOSR

OpticalBlack

MLI

MLI

MLI MLI MLI

FOSR

Aluminized FOSR

Silverized FOSR

Silverized FOSR

K1175_516

5-13

HST SYSTEMS

5-14

maneuver is in progress, the Safing System completesthe maneuver, then holds the Telescope in that position,suspending all science operations. Only ground controlcan return to science operations from Safemode.

If the system detects a marginal electrical powerproblem, or if an internal PCS safety check fails, theTelescope enters the Software Sun Point Mode. TheSafing System maneuvers the Telescope so the SAspoint toward the Sun to continuously generate solarpower. Telescope equipment is maintained within oper-ating temperatures and above survival temperatures,anticipating a return to normal operations. The STOCCmust intercede to correct the malfunction beforescience operations or normal functions can be resumed.

Since deployment of the Telescope in 1990, the SafingSystem has seen additional improvements to increaseits robustness to survive hardware failures and stillprotect the Telescope (refer to page 5-9, PointingControl Subsystem).

For the modes described above, the Safing System oper-ates through computer software. If conditions worsen,the system turns over control to the PSEA in HardwareSun Point Mode. Problems that could provoke thisaction include:• Computer malfunction• Batteries losing more than 50 percent of their charge• Two of the three RGAs failing• DMS failing.

If these conditions occur, the Advanced Computer stopssending keep-alive signals. This is the “handshake”mechanism between the flight software and the PSEA.

In Hardware Sun Point Mode, the PSEA computercommands the Telescope and turns off selected equip-ment to conserve power. Components shut downinclude the Advanced Computer and, within 2 hours,the SI C&DH. Before this happens, a payload (instru-ments) safing sequence begins and, if it has not alreadydone so, the Telescope turns the SAs toward the Sun,guided by the CSSs. The PSEA removes operatingpower from equipment not required for Telescopesurvival.

Once ground control is alerted to a problem, NASAmanagement of the STOCC convenes a failure analysisteam to evaluate the problem and seek the best andsafest corrective action while the Safing System main-tains control of the Telescope. The failure analysis teamis led by a senior management representative fromNASA/GSFC with the authority not only to call on theexpertise of engineers and scientists employed by NASAor its support contractors, but also to draft supportfrom any organization previously affiliated with the

Telescope Project. The team is chartered to identify thenature of the anomaly and to recommend correctiveaction. This recommendation is reviewed at a highermanagement level of NASA/GSFC. All changes to theTelescope’s hardware and all software configurationsrequire NASA Level I concurrence as specified in theHST Level I Operations Requirements Document.

Pointing/Safemode Electronics and Retrieval ModeGyro Assemblies. These assemblies are installed in Bay 8. The PSEA consists of 40 electronic printed-boardcircuits with redundant functions to run the Telescope,even in the case of internal circuit failure. It weighs 86 lb(39 kg). A backup gyroscope package, the RMGA, isdedicated for the PSEA. The RMGA consists of threegyroscopes. These are lower quality rate sensors thanthe RGAs because they are not intended for use duringobservations.

Optical Telescope Assembly

Perkin-Elmer Corporation (now Goodrich Corporation)designed and built the OTA. Although the OTA ismodest in size by ground-based observatory standardsand has a straightforward optical design, its accuracy—coupled with its place above the Earth’s atmosphere—renders its performance superior.

The OTA uses a “folded” design, common to large tele-scopes, which enables a long focal length of 189 feet(57.6 m) to be packaged into a small telescope length of21 feet (6.4 m). (Several smaller mirrors in the scienceinstruments are designed similarly to lengthen the lightpath within them.) This form of telescope is called aCassegrain. Its compactness is an essential componentof an observatory designed to fit inside the Shuttlecargo bay.

Conventional in design, the OTA is unconventional inother aspects. Large telescopes at ground-based sites arelimited in their performance by the resolution attain-able while operating under the Earth’s atmosphere, butthe HST orbits high above the atmosphere and providesan unobstructed view of the universe. For this reasonthe OTA was designed and built with exacting toler-ances to provide near-perfect image quality over thebroadest possible region of the spectrum.

Hubble’s OTA is a variant of the Cassegrain, called aRitchey-Chretien, in which both mirrors are hyper-boloidal in shape (having a deeper curvature than aparabolic mirror). This form is completely corrected forcoma (an image observation with a “tail”) and sphericalaberrations to provide an aplanatic system in whichaberrations are correct everywhere in the FOV. The onlyresidual aberrations are field curvature and astigmatism.

HST SYSTEMS

5-15

Both of these are zero exactly in the center of thefield and increase toward the edge of the field. Theseaberrations are easily corrected within the instru-ment optics.

Figure 5-17 shows the path of a light ray from adistant star as it travels through the Telescope to thefocus. Light travels down the tube, past baffles that

attenuate reflected light from unwanted brightsources, to the 94.5-inch (2.4-m) primary mirror.Reflecting off the front surface of the concave mirror,the light bounces back up the tube to the 12-inch(0.3-m)-diameter convex secondary mirror. The lightis now reflected and converged through a 23.5-inch(60-cm) hole in the primary mirror to the Telescopefocus, 3.3 feet (1.5 m) behind the primary mirror.

Four science instruments and three FGSs share thefocal plane by a system of mirrors. A small “folding”mirror in the center of the FOV directs light into theWFPC2. The remaining “science” field is dividedamong three axial science instruments, eachreceiving a quadrant of the circular FOV. Around theoutside of the science field, a “guidance” field isdivided among the three FGSs by their own foldingmirrors. Each FGS receives 60 arcmin2 of field in a90-degree sector. Figure 5-18 shows instrument/sensorfields of view.

The OTA hosts the science instruments and FGSs inthat it maintains the structural support and optical-image stability required for these instruments to fulfilltheir functions (see Fig. 5-19). Components of theOTA are the primary mirror, the secondary mirror, theFPS and the OTA Equipment Section. Perkin-Elmer

Corporation designed and built all the optical assemblies.Lockheed Martin built the OTA equipment section.

Primary Mirror Assembly and SphericalAberration

As the Telescope was first put through its paces onorbit in 1990, scientists discovered its primary mirror

had a spherical aberration. The outer edge of the 8-foot(2.4-m) primary mirror was ground too flat by awidth equal to 1/50 the thickness of a sheet of paper(about 2 microns). After the discovery, Ball Aerospacescientists and engineers built the Corrective OpticsSpace Telescope Axial Replacement (COSTAR). Itwas installed during the First Servicing Mission inDecember 1993 and brought the Telescope back to itsoriginal specifications.

The primary mirror assembly consists of the mirrorsupported inside the main ring, which is the struc-tural backbone of the Telescope, and the main andcentral baffles (see Fig. 5-20). This assembly providesthe structural coupling to the rest of the spacecraftthrough a set of kinematic brackets linking the mainring to the SSM. The assembly also supports theOTA baffles. Its major parts are:• Primary mirror• Main ring structure• Reaction plate and actuators• Main and central baffles.

Primary Mirror. The primary mirror blank, aproduct of Corning Glass Works, is known asultralow-expansion (ULE) glass. It was chosen for itsvery low-expansion coefficient, which ensures theTelescope minimum sensitivity to temperature

Fig. 5-17 Light path for the main Telescope

Aperture Door Secondary MirrorPrimaryMirror

Fine GuidanceSensor (3)

Axial ScienceInstrument (4)

Incoming Light

Stray-LightBaffles

SupportSystemsModule

Radial ScienceInstruments

Focal Plane(Image Formed Here)

K1175_517

HST SYSTEMS

5-16

Fig. 5-18 Instrument/sensor field of view after SM3B

Fig. 5-19 Optical Telescope Assembly components

SecondaryMirrorAssembly

Graphite EpoxyMetering Truss

Central Baffle

Support

Find GuidanceSensor (3)

Focal PlaneStructure

AxialScienceInstrument (4)

Fixed-HeadStar Tracker

Radial ScienceInstrument (1)

Main Ring

Primary Mirror

Electronic Boxes

AluminumMain Baffle

K1175_519

Space TelescopeImaging Spectrograph

+V3 Axis Fine Guidance Sensor 2

Corrective OpticsSpace TelescopeAxial Replacement

Fine GuidanceSensor 1

Advanced Camerafor Surveys

Wide Field and Planetary Camera 2

Incoming Image(View Looking Forward

+V1 Axis into Page)

Two Detectors,Separate Apertures

Near-InfraredCamera and Multi-ObjectSpectrometer

FineGuidanceSensor 3

Optical ControlSensor (3)

WFC

#3#2#1 14.1 arcmin

K1175_518

HST SYSTEMS

5-17

changes. The mirror is of a “sandwich” construction:two lightweight facesheets separated by a core, orfilling, of glass honeycomb ribs in a rectangular grid(see Fig. 5-21). This construction results in an 1800-pound (818-kg) mirror instead of an 8000-poundsolid-glass mirror.

Perkin-Elmer ground the mirror blank, 8 feet (2.4 m)

in diameter, to shape in its large optics fabricationfacility. When it was close to its final hyperboloidalshape, the mirror was transferred to the company’scomputer-controlled polishing facility.

After being ground and polished, the mirror wascoated with a reflective layer of aluminum and aprotective layer of magnesium fluoride only 0.1- and0.025-micrometer thick, respectively. The fluoridelayer protects the aluminum from oxidation andenhances reflectance at the important hydrogen emis-sion line known as Lyman-Alpha. The reflectivequality of the mirror is better than 70 percent at 1216angstroms (Lyman-Alpha) in the ultraviolet spectralrange and better than 85 percent for visible light.

The primary mirror is mounted to the main ringthrough a set of kinematic linkages. The linkagesattach to the mirror by three rods that penetrate theglass for axial constraint and by three pads bondedto the back of the glass for lateral support.

Main Ring. The main ring encircles the primarymirror; supports the mirror, the main baffle andcentral baffle, and the metering truss; and integratesthe elements of the Telescope to the spacecraft (seeFig. 5-22). This titanium ring, weighing 1200 pounds(545.5 kg), is a hollow box beam 15 inches (38 cm)thick with an outside diameter of 9.8 ft (2.9 m). It issuspended inside the SSM by a kinematic support.

Reaction Plate. The reaction plate is a wheel of I-beams forming a bulkhead behind the main ring,spanning its diameter. It radiates from a central ringthat supports the central baffle. Its primary functionis to carry an array of heaters that warm the back ofthe primary mirror, maintaining its temperature at70 degrees Fahrenheit. Made of lightweight, stiffberyllium, the plate also supports 24 figure-controlactuators attached to the primary mirror andarranged around the reaction plate in two concentric

Fig. 5-20 Primary mirror assembly

Fig. 5-21 Primary mirror construction Fig. 5-22 Main ring and reaction plate

Central Baffle Bracket (5)RadialI-Beam (15)

Figure ControlActuator (24)

Main Ring

Mirror Pad(24)Flexure

Mount (15)

AxialMount(15)

IntercostalRib (48)

Central Ring

K1175_522

MirrorConstruction

FrontFacesheet

InnerEdgeband

LightweightCore

OuterEdgeband

RearFacesheet

The mirror is made of Corning Code 7971ultralow expansion (ULE) silica glass

K1175_521

Primary Mirror Assembly

Main Baffle

Primary Mirror

Mirror Mount

Actuator (Typical)

Reaction Plate

Support SystemsModule AttachmentBrackets

Main Ring

Central Baffle

K1175_520

HST SYSTEMS

5-18

circles. These can be commandedfrom the ground, if necessary, tomake small corrections to theshape of the mirror.

Baffles. The OTA’s bafflesprevent stray light from brightobjects—such as the Sun, Moonand Earth—from reflecting downthe Telescope tube to the focalplane. The primary mirrorassembly includes two baffles.Attached to the front face of themain ring, the outer (main) baffleis an aluminum cylinder 9 feet(2.7 m) in diameter and 15.7 feet(4.8 m) long. Internal fins help itattenuate stray light. The centralbaffle is 10 feet (3 m) long, cone-shaped and attached to the reac-tion plate through a hole in thecenter of the primary mirror. Itextends down the centerline ofthe Telescope tube. The baffleinteriors are painted flat black tominimize light reflection.

Secondary Mirror Assembly

The Secondary Mirror Assemblycantilevers off the front face ofthe main ring and supports thesecondary mirror at exactly thecorrect position in front of the

primary mirror. This positionmust be accurate within 1/10,000inch whenever the Telescope isoperating. The assembly consistsof the mirror subassembly, a lightbaffle and an outer graphite-epoxy metering truss supportstructure (see Fig. 5-23).

The Secondary Mirror Assemblycontains the mirror, mounted onthree pairs of alignment actuatorsthat control its position andorientation. All are enclosedwithin the central hub at theforward end of the truss support.

The secondary mirror has amagnification of 10.4X. Itconverts the primary-mirrorconverging rays from f/2.35 to afocal ratio system prime focus off/24 and sends them back towardthe center of the primary mirror,where they pass through thecentral baffle to the focal point.The mirror is a convex hyper-boloid 12 inches (0.3 m) in diam-eter and made of Zerodur glasscoated with aluminum andmagnesium fluoride. Steeplyconvex, it has a surface accuracyeven greater than that of theprimary mirror.

Ground command adjusts theactuators to align the secondarymirror to provide perfect imagequality. The adjustments arecalculated from data picked up bytiny optical control systemsensors located in the FGSs.

The principal structural elementof the Secondary Mirror Assemblyis the metering truss, a cage with48 latticed struts attached to threerings and a central support struc-ture for the secondary mirror. Thetruss, 16 feet (4.8 m) long and 9 feet (2.7 m) in diameter, is agraphite, fiber-reinforced epoxystructure. Graphite was chosenfor its high stiffness, light weightand ability to reduce the struc-ture’s expansiveness to nearlyzero. This is vital because thesecondary mirror must stayperfectly placed relative to theprimary mirror, accurate to within0.0001 inch (2.5 micrometers)when the Telescope operates.

The truss attaches at one end tothe front face of the main ring ofthe Primary Mirror Assembly.The other end has a central hubthat houses the secondary mirrorand baffle along the optical axis.Aluminized mylar MLI in thetruss compensates for tempera-ture variations of up to 30degrees Fahrenheit when theTelescope is in Earth’s shadow sothe primary and secondarymirrors remain aligned.

The conical secondary mirrorsubassembly light baffle extendsalmost to the primary mirror. Itreduces stray bright-object lightfrom sources outside theTelescope FOV.

Fig. 5-23 Secondary mirror assembly

Shroud

Base Plate

Actuator Pair

Secondary Mirror

SecondaryMirror Baffle

Actuator Pair

Clamp

Flexure

K1175_523

HST SYSTEMS

Focal Plane StructureAssembly

The FPS is a large optical benchthat physically supports thescience instruments and FGSs andaligns them with the image focalplane of the Telescope. The -V3side of the structure, away fromthe Sun in space, supports theFHSTs and RSUs (see Fig. 5-24). It also provides facilities for on-orbit replacement of any instru-ments and thermal isolationbetween instruments.

The structure is 7 feet (2.1 m) by10 feet (3.04 m) long and weighsmore than 1200 pounds (545.5 kg).Because it must have extremethermal stability and be stiff,lightweight and strong, the FPS isconstructed of graphite-epoxy,augmented with mechanicalfasteners and metallic joints atstrength-critical locations. It isequipped with metallic mountsand supports for OrbitalReplacement Units (ORU) usedduring maintenance.

The FPS cantilevers off the rearface of the main ring, attached ateight flexible points that adjustto eliminate thermal distortions.The structure provides a fixedalignment for the FGSs. It hasguiderails and latches at eachinstrument mounting location soShuttle crews can easily exchangescience instruments and otherequipment in orbit.

OTA Equipment Section

The OTA Equipment Section is alarge semicircular set of compart-ments mounted outside thespacecraft on the forward shell ofthe SSM (see Fig. 5-25). Itcontains the OTA ElectricalPower and Thermal ControlElectronics (EP/TCE) System,Fine Guidance Electronics (FGE),Actuator Control Electronics(ACE), Optical ControlElectronics (OCE) and the fourthDMS DIU. The OTA EquipmentSection has nine bays: seven forequipment storage and two forsupport. All bays have outward-opening doors for easy astronautaccess, cabling and connectors for

the electronics, and heaters andinsulation for thermal control.

The EP/TCE System distributespower from the SSM EPS and theOTA system. Thermostats regu-late mirror temperatures andprevent mirror distortion fromthe cold of space. The electricaland thermal electronics alsocollect thermal sensor data fortransmission to the ground.

Three FGE units provide power,commands and telemetry to theFGSs. The electronics performcomputations for the sensors andinterface with the spacecraftpointing system for effectiveTelescope line-of-sight pointing

Fig. 5-24 Focal plane structure

Fig. 5-25 Optical Telescope Assembly Equipment Section

Looking Forward-V2

-V3

V2

V3V1

Fine GuidanceElectronics

DIUACE

Data Interface Unit

OpticalControl Electronics

Fine GuidanceElectronics

ActuatorControl Electronics

MultilayerInsulation on Doors

Electrical Power/Thermal ControlElectronics

K1175_525

A

BC

DEF

GH

J

Primary Mirror Main Ring

Focal Plane Structure

Axial Science Instrument

Science InstrumentLatching Mechanism

Fixed-HeadStar Tracker (3)

Crew System Handle

Rate SensingUnit for Rate GyroAssemblies (3)

Science InstrumentConnectorPanel

K1175_524

5-19

HST SYSTEMS

5-20

and stabilization. There is a guidance electronicsassembly for each guidance sensor.

The ACE unit provides the command and telemetryinterface to the 24 actuators attached to the primarymirror and to the six actuators attached to thesecondary mirror. These electronics select whichactuator to move and monitor its response to thecommand. Positioning commands go from theground to the electronics through the DIU.

The OCE unit controls the optical control sensors.These white-light interferometers measure theoptical quality of the OTA and send the data to theground for analysis. There is one optical controlsensor for each FGS, but the OCE unit runs allcontrol sensors. The DIU is an electronic interfacebetween the other OTA electronics units and theTelescope command and telemetry system.

Fine Guidance Sensor

Three FGSs are located at 90-degree intervals aroundthe circumference of the focal plane structure,between the structure frame and the main ring. Eachsensor measures 5.4 feet (1.5 m) long and 3.3 feet (1 m)wide and weighs 485 pounds (220 kg).

Each FGS enclosure houses a guidance sensor and awavefront sensor. The wavefront sensors areelements of the optical control sensor used to alignand optimize the optical system of the Telescope.

The Telescope’s ability to remain pointing at adistant target to within 0.005 arcsec for long periodsof time is due largely to the accuracy of the FGSs.They lock on a star and measure any apparentmotion to an accuracy of 0.0028 arcsec. This is equiv-alent to seeing from New York City the motion of alanding light on an aircraft flying over San Francisco.

When two sensors lock on a target, the third meas-ures the angular position of a star, a process calledastrometry. Sensor astrometric functions arediscussed in Section 4, Science Instruments. DuringSM2 a re-certified FGS (S/N 2001) was installed as areplacement in the HST FGS Bay 1. During SM3A are-certified FGS (S/N 2002) was installed in the HSTFGS Bay 2.

FGS Composition and Function

Each FGS consists of a large structure housing acollection of mirrors, lenses, servos to locate animage, prisms to fine-track the image, beam splittersand four photomultiplier tubes (see Fig. 5-26). The

entire mechanism adjusts to move the Telescope intoprecise alignment with a target star. Each FGS has alarge (60 arcmin2) FOV to search for and track stars,and a 5.0 arcsec2 FOV used by the detector prisms topinpoint the star.

The sensors work in pairs to aim the Telescope. TheGuide Star Selection System, developed by theScience Institute, catalogs and charts guide stars neareach observation target to make it easier to find thetarget. One sensor searches for a target guide star.After the first sensor locks onto a guide star, thesecond sensor locates and locks onto another targetguide star. Once designated and located, the guidestars keep the image of the observation target in theaperture of the selected science instrument.

Each FGS uses a 90-degree sector of the Telescope’sFOV outside the central “science” field. This regionof the FOV has the greatest astigmatic and curvaturedistortions. The size of the FGS’s FOV was chosento heighten the probability of finding an appropriateguide star, even in the direction of the lowest starpopulation near the galactic poles.

An FGS “pickoff” mirror intercepts the incomingstellar image and projects it into the sensor’s largeFOV. Each FGS FOV has 60 arcmin2 available. Theguide star of interest can be anywhere within thisfield. After finding the star, the sensor locks onto itand sends error signals to the Telescope, telling ithow to move to keep the star image perfectly still.Using a pair of star selector servos, the FGS can moveits line of sight anywhere within its large FOV. Each

Fig. 5-26 Cutaway view of Fine Guidance Sensor

EnclosureAspheric CollimatingMirror

Pinhole/LensAssembly (4)

DoubletLens (4)

Koesters’Prisms

Filter (5)

Pickoff Mirror

StarSelectorMirrors

Corrector GroupDeviationPrism

Optical Bench

K1175_526

HST SYSTEMS

5-21

can be thought of as an optical gimbal: one servomoves north and south, the other east and west.They steer the small FOV (5 arcsec2) of the FGSdetectors to any position in the sensor field. Encoderswithin each servo system send back the exact coordi-nates of the detector field centers at any point.

Because the exact location of a guide star may beuncertain, the star selector servos also can cause thedetector to search the region around the most prob-able guide star position. It searches in a spiralpattern, starting at the center and moving out untilit finds the guide star it seeks. Then the detectors arecommanded to go into fine-track mode and hold thestar image exactly centered in the FOV while thestar selector servo encoders send information aboutthe position of the star to the spacecraft PCS.

The detectors are a pair of interferometers, calledKoester’s prisms, coupled to photomultiplier tubes(see Fig. 5-27). Each detector operates in one axis, sotwo detectors are needed. Operating on theincoming wavefront from the distant guide star, theinterferometers compare the wave phase at one edgeof the Telescope’s entrance aperture with the phaseat the opposite edge. When the phases are equal, thestar is exactly centered. Any phase difference showsa pointing error that must be corrected.

Along the optical path from Telescope to detector areadditional optical elements that turn or fold thebeam to fit everything inside the FGS enclosure andto correct the Telescope’s astigmatism and fieldcurvature. All optical elements are mounted on atemperature-controlled, graphite-epoxy compositeoptical bench.

Articulated Mirror System

Analysis of the FGS on-orbit data revealed thatminor misalignments of the optical pupil centeringon Koester’s prism interferometer in the presence ofspherical aberration prevented the FGS fromachieving its optimum performance. During therecertification of FGS (S/N 2001), fold flat #3 in theradial bay module optical train was mechanized toallow on-orbit alignment of the pupil.

Implementation of this system utilized existingsignals and commands by rerouting them with aunique interface harness enhancement kit (OCE-EK)interfacing the OCE, the DIU and the Fine GuidanceSystem/Radial Bay Module (FGS/RBM). The OCE-EK was augmented with the Actuator MechanismElectronics (AME) and the fold flat #3 ActuatorMechanism Assembly (AMA) located internal to theFGS/RBM. Ground tests indicate a substantialincrease in FGS performance with this innovativedesign improvement.

Solar Arrays

New rigid solar arrays will be attached to theTelescope during SM3B. The original arrays fitted toHubble—designed by the European Space Agencyand built by British Aerospace, Space Systems—aretwo large rectangular wings of retractable solar cellblankets fixed on a two-stem frame. The blanketunfurls from a cassette in the middle of the wing. Aspreader bar at each end of the wing stretches theblanket and maintains tension.

Following deployment in 1990, engineers discoveredtwo problems: a loss of focus and images thatjittered briefly when the Telescope flew into and outof Earth’s shadow. The jitter problem was traced tothe two large SAs. Abrupt temperature changes,from -150 to 200 degrees Fahrenheit during orbit,caused the panels to distort twice during each orbit.As a temporary fix, software was written thatcommanded the PCS to compensate for the jitterautomatically. The problem was mitigated duringSM1 by the replacement of the old arrays with newones that had been modified to reduce thermalswings of the bi-stems.

The two new solar array wings to be installed onSM3B are assembled from eight panels built atLockheed Martin Space Systems Company inSunnyvale, California, and designed originally for thecommercial Iridium communications satellites. AtGoddard Space Flight Center in Greenbelt,Maryland, four panels were mounted onto eachaluminum-lithium support wing structure.

Fig. 5-27 Optical path of Fine Guidance Sensor

K1175_527

OpticalTelescopeAssembly

CollimatorFirst Star Selector

Refractive GroupSecond Star Selector

BeamSplitter

Pupil

Rotated90 deg

Field Lensand Field Stop

Phototube

First PupilKoesters’ Prism

Doublet

HST SYSTEMS

5-22

The new wing assemblies, whichhave higher efficiency GalliumArsenide solar cells, will giveHubble approximately 20 percentmore power than the currentarrays. In addition, their smallercross section and rigidity willreduce aerodynamic drag andproduce significantly less vibra-tion than the existing wings (seeFig. 5-28).

New Solar Array DriveMechanisms (SADM) also will beinstalled during SM3B. Thesemechanisms will maneuver thenew arrays to keep themconstantly pointed at the Sun.The European Space Agency(ESA) designed, developed andtested the SADMs. ESA used itsworld-class test facility in TheNetherlands to subject the newarrays and drive mechanisms torealistic simulations of theextreme temperature cyclesencountered in Hubble’s orbit—including sunrise and sunset.

Science InstrumentControl and DataHandling Unit

The SI C&DH unit keeps allscience instrument systemssynchronized. It works with theDMU to process, format,temporarily store on the datarecorders or transmit science andengineering data to the ground.

Components

The SI C&DH unit is a collectionof electronic componentsattached to an ORU traymounted on the door of Bay 10 inthe SSM Equipment Section (seeFig. 5-29). Small Remote InterfaceUnits (RIU), also part of thesystem, provide the interface toindividual science instruments.

Components of the SI C&DHunit are:

• NASA Standard SpacecraftComputer (NSCC-I)

• Two standard interface circuitboards for the computer

• Two control units/science dataformatter units (CU/SDF)

• Two CPU modules • A PCU • Two RIUs • Various memory, data and

command communicationslines (buses) connected bycouplers.

These components are redundantso the system can recover fromany single failure.

NASA Computer. The NSSC-Ihas a CPU and eight memorymodules, each holding 8,192eighteen-bit words. One embeddedsoftware program (the “execu-tive”) runs the computer. It movesdata, commands and operationprograms (called applications) forindividual science instruments inand out of the processing unit.The application programs monitorand control specific instruments,and analyze and manipulate thecollected data.

The memory stores operationalcommands for execution whenthe Telescope is not in contact

Item

SA2Flexible Array

4600 W at6 years(actual)

39.67 ft x 9.75 ft(12.1 m x 3.3 m)

339 lbper wing

Actual on-orbit performancemeasured at Winter Solstice,December 2000

Power Size Weight Comments

SA3Rigid Array

5270 W at6 years(predicted)

24.75 ft x 8.0 ft(7.1 m x 2.6 m)

640 lbper wing

Increased capability forplanned science

Less shadowing and blockage

Fig. 5-28 Solar Array wing detail comparison

39.67 ft (12.1 m)

9.75 ft(3.3 m)

8.0 ft(2.6 m)

24.75 ft (7.1 m)

K1175_528

K1175_528A

SA2 Flexible Array

SA3 Rigid Array

HST SYSTEMS

5-23

with the ground. Each memoryunit has five areas reserved forcommands and programs uniqueto each science instrument. Thecomputer can be reprogrammedfrom the ground for futurerequests or for working aroundfailed equipment.

Standard Interface Board. Thecircuit board is the communica-tions bridge between thecomputer and the CU/SDF.

Control Unit/Science DataFormatter. The heart of the SIC&DH unit is the CU/SDF. Itformats and sends all commandsand data to designated destina-tions such as the DMU of theSSM, the NASA computer andthe science instruments. The unithas a microprocessor for controland formatting functions.

The CU/SDF receives groundcommands, data requests, scienceand engineering data, and systemsignals. Two examples of systemsignals are “time tags”—clocksignals that synchronize theentire spacecraft—and “processorinterface tables”—communica-

tions codes.The CU/SDFtransmitscommandsand requestsafter format-ting them sothat thespecific desti-nation unitcan readthem. Forexample,groundcommandsand SSMcommandsare trans-mitted withdifferentformats.Groundcommands

use 27-bit words and SSMcommands use 16-bit words. Theformatter translates eachcommand signal into a commonformat. The CU/SDF also refor-mats and sends engineering andscience data. Onboard analysis ofthe data is an NSSC-I function.

Power Control Unit. The PCUdistributes and switches poweramong components of the SIC&DH unit. It conditions thepower required by each unit. Forexample: The computer memoryboards typically need +5 volts, -5 volts and +12 volts while theCU/SDF requires +28 volts. ThePCU ensures that all voltagerequirements are met.

Remote Interface Unit. RIUstransmit commands, clock andother system signals, and engi-neering data between thescience instruments and the SIC&DH unit. However, the RIUsdo not send science data. Thereare six RIUs in the Telescope:five attached to the scienceinstruments and one dedicatedto the CU/SDF and PCUs in theSI C&DH unit. Each RIU can be

coupled with up to twoexpander units.

Communications Buses. The SIC&DH unit contains data bus linesthat pass signals and data betweenthe unit and the science instru-ments. Each bus is multiplexed:one line sends system messages,commands and engineering datarequests to the module units, and areply line transmits requestedinformation and science data backto the SI C&DH unit. A couplerattaches the bus to each remoteunit. This isolates the module ifthe RIU fails. The SI C&DHcoupler unit is on the ORU tray.

Operation

The SI C&DH unit handlesscience instrument system moni-toring (such as timing and systemchecks), command processing anddata processing.

System Monitoring. Engineeringdata tells the monitoringcomputer whether instrumentsystems are functioning. Atregular intervals, varying fromevery 500 milliseconds to every40 seconds, the SI C&DH unitscans all monitoring devices forengineering data and passes datato the NSCC-I or SSM computer.The computers process or storethe information. Any failureindicated by these constant testscould initiate a “safing hold”situation (refer to page 5-13,Safing (Contingency) System),and thus a suspension of scienceoperations.

Command Processing. Figure 5-30shows the flow of commandswithin the SI C&DH unit.Commands enter the CU/SDF(bottom right in the drawing)through the SSM Command DIU(ground commands) or the DIU(SSM commands). The CU/SDFchecks and reformats thecommands, which then go either

Fig. 5-29 Science Instrument Control and Data Handling unit

K1175_529

Two CentralProcessorModules

Extravehicular Activity Handle

A118A118A118A118

A109

A120 FourMemories

RemoteInterface Unit

A231

A300

A230

A210

A300

A211

Control Unit/Science Data Formatter Power Control Unit

Orbital ReplacementUnit Tray

Bus Coupler Unit A240

Control Unit/Science DataFormatter

RemoteInterface Unit

FourMemoriesTwo Standard

Interfaces

HST SYSTEMS

5-24

to the RIUs or to the NSCC-I for storage. “Time-tagged” commands, stored in the computer’s memory(top right of drawing), also follow this process.

Each command is interpreted as “real time,” as if theSI C&DH just received it. Many commands actuallyare onboard stored commands activated by certainsituations. For example, when the Telescope is posi-tioned for a programmed observation using the SpaceTelescope Imaging Spectrograph, that program is acti-vated. The SI C&DH can issue certain requests to theSSM, such as to execute a limited number of pointingcontrol functions to make small Telescope maneuvers.

Science Data Processing. Science data can comefrom all science instruments at once. The CU/SDFtransfers incoming data through computer memorylocations called packet buffers. It fills each buffer inorder, switching among them as the buffers fill andempty. Each data packet goes from the buffer to theNSCC-I for further processing, or directly to theSSM for storage in the data recorders or transmis-sion to the ground. Data returns to the CU/SDFafter computer processing. When transmitting, theCU/SDF must send a continuous stream of data,either full packet buffers or empty buffers calledfiller packets, to maintain a synchronized link with

the SSM. Special checking codes (Reed-Solomon andpseudo-random noise) can be added to the data asoptions. Figure 5-30 shows the flow of science datain the Telescope.

Space Support Equipment

Hubble was designed to be maintained, repaired andenhanced while in orbit, extending its life and useful-ness. For servicing, the Space Shuttle will captureand position the Telescope vertically in the aft end ofthe cargo bay, then the crew will perform mainte-nance and replacement tasks. The Space SupportEquipment (SSE) provides a maintenance platform tohold the Telescope, electrical support of theTelescope during servicing and storage for replace-ment components known as ORUs.

The major SSE items to be used for SM3B are theFlight Support System (FSS) and and ORU Carriers(ORUC), comprising the Rigid Array Carrier (RAC),the Second Axial Carrier (SAC) and the Multi-UseLightweight Equipment (MULE) carrier. Crew aidsand tools also will be used during servicing. Section 2of this guide describes details specific to SM3B.

Fig. 5-30 Command flow for Science Instrument Control and Data Handling unit K1175_530

RemoteModules

RemoteModules

RemoteModules

RemoteModules

RemoteModules

RemoteModules

To S

cien

ce I

nstr

umen

ts 1

– 5

Com

mands

Supervisory Bus

To PowerControl Unit

StoredCommand Memory

Science Instrument

Unique Memory

NASA Standard Spacecraft ComputerModel-I and Standard Interface

StoredCommand

OutputBuffer

Science Instrument

Unique Memory

Science Instrument

Unique Memory

Science Instrument

Unique Memory

Science Instrument

Unique Memory

Science Instrument

Unique Memory

Data M

anagement

Units 6 and 7

Tim

e Tags and Com

mands

Data M

anagement

Unit 1

Com

puter Com

mands

Data M

anagement

Units 4 and 5

Support SystemsModule ProcessorInterface Table Words

Reformat

Word Order,Time Tag andParity Checks

CU/SDFCommandProcessing

Control

Control Unit/Science Data Formatter (CU/SDF)

ToCU/SDFLogic

Parity and Type Code

Checks

Parity andWord Order

Checks

From CommandData Interface

27-bit Commands

16-bit Commands

From DataInterface Unit

HST SYSTEMS

5-25

Orbital Replacement Unit Carrier

An ORUC is a pallet outfitted with shelves and/orenclosures that is used to carry replacements intoorbit and to return replaced units to Earth. For SM3Bthe Columbia payload bay will contain three ORUCs.All ORUs and scientific instruments are carriedwithin protective enclosures to provide them a benignenvironment throughout the mission. The enclosuresprotect the instruments from contamination andmaintain the temperature of the instruments orORUs within tight limits. Instruments are mountedin the enclosures using the same manually drivenlatch system that holds instruments in the Telescope.

During the change-out process, replaced scienceinstruments are stored temporarily in the ORUC. Atypical change-out begins with an astronautremoving the old instrument from the Telescope andattaching it to a bracket on the ORUC. The astronautthen removes the new instrument from its protectiveenclosure and installs it in the Telescope. Finally, theastronaut places the old instrument in the appro-priate protective enclosure for return to Earth.

The ORUC receives power for its TCS from the FSS.The carrier also provides temperature telemetry datathrough the FSS for readout in the Shuttle and onthe ground during the mission.

Crew Aids

Astronauts perform extravehicular activities usingmany tools to replace instruments and equipment,to move around the Telescope and the cargo bay, andto operate manual override drives. Tools and equip-ment, bolts, connectors and other hardware are stan-dardized not only for the Telescope but also betweenthe Telescope and the Shuttle. For example, grap-pling receptacles share common features.

To move around the Telescope, the crew uses 225feet of handrails encircling the spacecraft. The railsare painted yellow for visibility. In addition, thecrew can hold onto guiderails, trunnion bars andscuff plates fore and aft.

Astronauts can install portable handhold plates wherethere are no permanent holds, such as on the FGS.Another tool is the Portable Foot Restraint (PFR).

While the astronauts work, they use tethers to hooktools to their suits and tie replacement units to theTelescope. Each crew member has a ratchet wrenchto manually crank the antenna and array masts ifpower for the mast drives fails. A power wrench alsois available if hand-cranking is too time consuming.Other hand tools include portable lights and ajettison handle, which attach to sockets on the aper-ture door and to the SA wings so the crew can pushthe equipment away from the Telescope.

Fig. 5-31 Flow of science data in the Hubble Space Telescope

K1175_531

PN

Code

(Only if P

N

Encoding

Selected)

Reed-S

olomon C

heckbit Segm

ents

(Only if R

eed-Solom

onE

ncoding Selected)

Science D

ata Packet S

egments

Science Instrum

ents

Direct M

emory A

ccess 5R

aw S

cience Data

Direct M

emory A

ccess 3

Control W

ordsD

irect Mem

oryA

ccess 8

Direct M

emory

Access 3

Control W

ordsC

ontrol

Direct M

emory A

ccess 14

NA

SA

Model-I C

omputer

Data Logs and P

rocessed Science D

ata

Ancillary D

ata

Science D

ataInput S

election Logic

NASA Standard Spacecraft Computer Model-Iand Standard Interfaces

Control Logic

Control Commands

Control Unit/ScienceData Formatter Logic

Raw Science

Data

FromCentral Unit/Science DataFormatterCommandProcessing

Control Unit/ScienceData Formatter Logic

To Data Management Unit

Packet Buffer 1

Raw or Packetized Data

Time Tag

Format RAM and ROM

Time Tag

Packet Buffer 2

Control Unit/Science Data

FormatterTimer

DestinationSwitch

(1 Per ScienceInstrument)

FillerPackets

ControlSwitch

ControlSwitch

Reed-SolomonEncoder

Science Data Bit Stream

End of Period

PseudorandomNoise CodeGenerator

6-1

ubble Space Telescopeoperations comprise (1) science operations and

(2) mission operations. Scienceoperations plan and conduct theHST science program—observingcelestial objects and gatheringdata. Mission operationscommand and control HST toimplement the observationschedule and maintain theTelescope’s overall performance.

These two types of operationsoften coincide and interact. Forexample, a science instrumentmay observe a star and calibrateincoming wavelengths againststandards developed during scien-

tific verification. Mission opera-tions monitor observations toensure that Telescope subsystemshave functioned correctly.

The HST ground system carriesout day-to-day mission operations.This system consists of the SpaceTelescope Operations ControlCenter (STOCC) and other facili-ties at the Space Telescope ScienceInstitute (STScI) in Baltimore,Maryland, and the PacketProcessing Facility (PACOR) andother institutional facilities atGoddard Space Flight Center(GSFC) in Greenbelt, Maryland. Asecond STOCC at GSFC conductsthe Servicing Missions.

Space Telescope ScienceInstitute

The STScI oversees science oper-ations for GSFC. Among its func-tions are to:• Host astronomers.• Evaluate proposals and choose

observation programs.• Schedule the selected observa-

tions and assist guest observersin their work.

• Generate an overall missiontimeline and commandsequences.

• Store and analyze science datafrom the Telescope.

HST OPERATIONS

H

HST OPERATIONS

6-2

STScI also monitors theTelescope and science instru-ments for characteristics thatcould affect science data collec-tion, such as instrument perform-ance quality, pointing inaccura-cies and Telescope focus.

The flight operations teamconducts mission operationsfrom STOCC.

Scientific Goals

The Association of Universitiesfor Research in Astronomy(AURA) operates STScI. AURA isa consortium of 29 United Statesuniversities that run severalnational facilities for astronomy.

STScI helps conduct the scienceprogram to meet the overallscientific goals of the Telescopeprogram, set by the Institute andNASA in consultation withAURA’s Space Telescope InstituteCouncil and committees repre-senting the international astro-nomical community.

STScI Software

Computer hardware and softwareplay an important role in STScIwork, including a mission plan-ning and scheduling system and ascience data processing system.STScI also created a guide starcatalog used to support theprecise pointing requirements ofthe HST pointing controlsubsystem. In addition, ScienceData Analysis Software (SDAS)provides analytical tools forastronomers studying observa-tional data.

As part of the Planning andScheduling System, the STScIGuide Star Selection System(GSSS) provides reference starsand other bright objects so theFine Guidance Sensors (FGS) canpoint the Telescope accurately.GSSS selects guide stars that canbe located unambiguously in thesky when the sensors point the

Telescope. The guide star cataloghas information on 20 millioncelestial objects, created from1,477 photographic survey platescovering the entire sky.

After STScI collects, edits, meas-ures and archives science data,observers can use SDAS toanalyze and interpret the data.

Selecting ObservationProposals

Astronomers worldwide may usethe Telescope. Any scientist maysubmit a proposal to STScIoutlining an observing programand describing the scientific objec-tives and instruments required.

STScI evaluates these requests fortechnical feasibility, conducts peerreviews and then chooses thehighest ranked proposals. Thefinal decision rests with the STScIdirector, advised by a reviewcommittee of astronomers andscientists from many institutions.

Because individual astronomersand astronomy teams submitmany more proposals than canpossibly be accepted, STScIencourages a team approach.

Scheduling TelescopeObservations

The primary scheduling consider-ation is availability of a target,which may be limited by environ-mental and stray-lightconstraints. For example, a faintobject occasionally must beobserved when the Telescope is inEarth’s shadow. The scheduletakes into consideration systemlimits, observations that use morethan one instrument and requiredtime for special observations.

Data Analysis and Storage

STScI is responsible for storingthe massive amount of datacollected by the Telescope. TheHubble Data Archive catalog

records the location and status ofdata as it pours into the storagebanks. Observers and visitingastronomers can easily retrievethe stored data for examinationor use data manipulation proce-dures created by the STScI.

The European Space Agency(ESA) provides approximately 15 staff members co-located withSTScI staff and operates its owndata analysis facility in Garching,Germany.

In addition to science data, theSTScI stores engineering data.This is important for developingmore efficient use of theTelescope systems and foradjusting Telescope operationsbased on engineering findings, forexample, if an instrumentprovides unreliable data in certaintemperature ranges.

STScI processes all data within24 hours after receipt. WhenSTScI receives science data fromPACOR, it automatically formatsthe data and verifies its quality.STScI also calibrates data toremove the instrument’s proper-ties such as a variation in thedetector’s sensitivity across thedata field. Then the softwareplaces the data on digital archivemedia from which the data canbe formatted and distributed toan observer or archival researcher.

Space TelescopeOperations ControlCenter

The STOCC flight operationteam runs day-to-day spacecraftoperations at STScI. In addition,the STOCC team works with theNASA Communications Network(NASCOM) and the Tracking andData Relay Satellite System(TDRSS) to facilitate HST datacommunications.

NASA built the Vision 2000Control Center System (CCS)specifically to support the HST

HST OPERATIONS

6-3

Third Servicing Missions (SM3Aand SM3B). The CCS providesdistributed capabilities with acompletely new user interfacethat is on the forefront of space-craft operations.

STOCC has three major opera-tional responsibilities:• Spacecraft operations,

including sending commands tothe spacecraft

• Telemetry processing• Offline support.

Most spacecraft operations derivefrom time-tagged commandsmanaged by the Telescope’sonboard software. Using theCCS, the STOCC flight opera-tions team uplinks the commandsto the HST computers.

Engineering telemetry, received inthe STOCC from the GSFC insti-tutional communication system,provides information on the HSTspacecraft subsystem status. Forexample, telemetry can verifyPointing Control System opera-tion and stability performance ofthe Telescope. Many cases requireconsultation between STOCCand STScI, particularly if the dataaffects an ongoing observation.

An important part of the groundsystem is PACOR processing.When data arrives fromNASCOM for science handling,PACOR reformats the data,checks for noise or transmissionproblems, and passes the data tothe STScI along with a dataquality report.

Another important STScI func-tion is to support observersrequiring a “quick-look” analysisof data. STScI alerts PACOR tothat need, and the incoming datacan be processed for theobservers.

TDRSS has two communicationsrelay satellites 130 degrees apartand a ground terminal at WhiteSands, New Mexico. There is a

small “zone of exclusion” whereEarth blocks the Telescope signalto either satellite, but up to 91percent of the Telescope’s orbit iswithin communications coverage.Tracking and Data RelaySatellites (TDRS) receive andsend both single-access (sciencedata) and multiple-access(commands and engineeringdata) channels.

OperationalCharacteristics

Three major operational factorsaffect the success of the Telescope: • Orbital characteristics for the

spacecraft • Maneuvering characteristics • Communications characteris-

tics for sending and receivingdata and commands.

Orbital Characteristics

The Telescope’s orbit is approxi-mately 320 nmi (593 km). Theorbit inclines at a 28.5-degreeangle from the equator becausethe Shuttle launch was due eastfrom Kennedy Space Center. Thisorbit puts the Sun in theTelescope orbital plane so thatsunlight falls more directly onthe Solar Arrays. In addition, 320 nmi is high enough that aerodynamic drag from the faintatmosphere will not decay theTelescope’s orbit to below theminimum operating altitude.

HST completes one orbit every97 minutes, passing into theshadow of the Earth during eachorbit. The time in shadow variesfrom 28 to 36 minutes. During anominal 30-day period, the varia-tion is between 34.5 and 36minutes. If Earth blocks an objectfrom the Telescope, the Telescopereacquires the object as thespacecraft comes out of Earth’soccultation. Faint-object viewingis best while the Telescope is inEarth’s shadow.

TDRSS tracks the Telescope’s

orbit, plotting the orbit at leasteight times daily and sending thedata to the Flight DynamicsFacility at GSFC. Although thishelps predict future orbits, someinaccuracy in predicting orbitalevents, such as exit from Earth’sshadow, is unavoidable. The envi-ronmental elements with greatesteffect on the Telescope’s orbit aresolar storms and other solaractivities. These thicken theupper atmosphere and increasethe drag force on the Telescope,accelerating the orbit decay rate.

Celestial Viewing

As a normal orientation, theTelescope is pointed toward celes-tial targets to expose instrumentdetectors for up to 10 hours. Acontinuous-viewing zone exists,parallel to the orbit plane of theTelescope and up to 18 degrees oneither side of the north and southpoles of that orbital plane (see Fig.6-1). Otherwise, celestial viewingdepends on how long a targetremains unblocked by Earth.

The amount of shadow timeavailable for faint-object studyalso affects celestial observations.Shadow time for an observationvaries with the time of year andthe location of the target relativeto the orbit plane. Astronomersuse a geometric formula to decidewhen a target will be most visible.

Other sources affecting celestialviewing are zodiacal light and inte-grated or background starlight.

Solar System Object Viewing

The factors mentioned for celes-tial viewing also affect solarsystem objects. In addition, theTelescope works with impreciseorbit parameters for itself andobjects such as the outer planetsand comets. For example,Neptune’s center may be off by21 km when the sensors try tolock onto it because the Telescopeis changing its position in orbit,

altering the pointing direction tonearby objects. However, mostsolar system objects are sobright the Telescope needs only aquick snapshot of the object tofix its position. Tracking inaccu-racies are more likely to cause ablurred image if they occurduring long-exposure observa-tions of dim targets.

The Telescope’s roll attitude alsomay affect the view of the objectand require a maneuver that rollsthe spacecraft more than the 30-degree limit—for example, toplace the image into a spectro-graphic slit aperture.

Tracking interior planets(Mercury and Venus) with theTelescope places the Sun withinthe Telescope opening’s 50-degreeSun-exclusion zone. For thisreason, HST never observesMercury and has observed Venusonly once, using Earth to block(occult) the Sun.

Natural Radiation

Energetic particles from differentsources continuously bombardthe Telescope as it travels around

the Earth.Geomagneticshieldingblocks muchof the solarand galacticparticle radia-tion. Whenthe Telescopepassesthrough theSouth AtlanticAnomaly(SAA), a“hole” inEarth’smagneticfield, chargedparticles canenter theTelescope andstrike itsdetectors,emitting elec-

trons and producing false data.

The Telescope passes through theSAA for segments of eight or nineconsecutive orbits, then has nocontact with it for six or sevenorbits. Each encounter lasts up to25 minutes. In addition, the SAArotates with Earth, so it occasion-

ally coincides with the Telescopeas the spacecraft enters Earth-shadow observation periods.Careful scheduling minimizes theeffects of the anomaly, but it hassome regular impact.

Solar flares are strong pulses ofsolar radiation, accompanied bybursts of energetic particles.Earth’s magnetic field shields thelower magnetic latitude regions,such as the Telescope’s orbitinclination, from most of thesecharged particles. NASA regularlymonitors the flares, and theTelescope can stop an observationuntil the flares subside.

Maneuvering Characteristics

The Telescope changes its orien-tation in space by rotating itsreaction wheels, then slowingthem. The momentum changecaused by the reaction moves thespacecraft at a baseline rate of0.22 degree per second or 90degrees in 14 minutes. Figure 6-2shows a roll-and-pitch maneuver.When the Telescope maneuvers,it takes a few minutes to lockonto a new target and accumu-

HST OPERATIONS

6-4

Fig. 6-1 "Continuous-zone" celestial viewing

ContinuousViewing Zone

North OrbitalPole

18˚

Orbit Plane

EquatorialPlane

ContinuousViewing Zone

SouthOrbitalZone

K1175_601

Fig. 6-2 HST single-axis maneuversK1175_602

-V1

V1 (Roll) Maneuver(Viewing Away From Sun)

V2 (Pitch) Maneuvers(Maneuver plane contains Sun)

-V2

Sun

50˚

HST OPERATIONS

6-5

late drift errors. This means thata larger region of the sky must bescanned for guide stars.

One consideration with maneu-vering is the danger of movingthe Solar Array wings out of theSun’s direct radiation for toolong. Therefore, maneuversbeyond a certain range in angleand time are limited.

When the Telescope performs apitch to a target near the 50-degree Sun-avoidance zone, theTelescope curves away from theSun. For example, if two targetsare opposed at 180 degrees justoutside the 50-degree zone, theTelescope follows an imaginarycircle of 50 degrees around theSun until it locates the secondtarget (see Fig. 6-3).

CommunicationsCharacteristics

HST communicates with theground via TDRSS. With twosatellites 130 degrees apart inlongitude, the maximum amountof contact time is 94.5 minutesof continuous communication,with only 2.5 to 7 minutes in azone of exclusion out of reach ofeither TDRS (see Fig. 6-4).However, orbital variations bythe Telescope and communica-tions satellites slightly widenthe zone of exclusion.

GSFC’s Network Control Center(NCC) schedules all TDRS

communications. The Telescopehas a general orbital communica-tion schedule, supplemented byspecific science requests. The NCCprepares schedules 14 days beforethe start of each mission week.

The backup communications linkis the Ground Network, whichreceives engineering data orscience data if the High GainAntennas (HGA) cannot transmitto TDRSS. The longest single

contact time is 8 minutes. Thelimiting factor of this backupsystem is the large gap in timebetween contacts with theTelescope. In practical terms, atleast three contacts are requiredto read data from a filled sciencedata recorder—with gaps of up to11 hours between transmissions.

To avoid unnecessary gaps incommunication, each HGA main-tains continuous contact withone TDRS. Each antenna tracksthe communication satellite, evenduring fine-pointing maneuvers.

Low Gain Antennas provide atleast 95 percent orbital coveragevia a TDRS for the minimummultiple-access command rateused.

Fig. 6-3 Sun-avoidance maneuver

K1175_603

Path of HST Slew(Facing Sun butangled 50˚ awayfrom direct contact)

Target 1

Target 2

50˚

50˚

50˚

50˚

Fig. 6-4 TDRS-HST contact zones

TDRS EastLongitude 41˚ W

TDRS West Longitude 171˚ W

TDRS WestShadow Zone

Earth

TDRS EastShadow Zone

No Coverage Zone K1175_604

Acquisition andObservation

The major steps in the observa-tion process are (1) target acqui-sition and observation, (2) datacollection and transmission and(3) data analysis.

Each science instrument has anentrance aperture, located indifferent portions of the Hubble’sfocal plane. These positions makeprecise pointing a sometimes-lengthy procedure for the FGSs,which must center the target insmall apertures. Additional timeis required to reposition theTelescope: an estimated 18minutes to maneuver 90 degreesplus the time the sensors take toacquire the guide stars. If theTelescope overshoots its target,the Fixed Head Star Trackers mayhave to make coarse-pointingupdates before the Telescope canuse the FGSs again.

To increase the probability of asuccessful acquisition, Telescope

flight software allows the use ofmultiple guide-star pairs toaccount for natural contingenciesthat might affect a guide-staracquisition—such as a guide starbeing a binary star andpreventing the FGSs from gettinga fine lock on the target.Therefore, an observer can submita proposal that includes amultiple selection of guide-starpairs. If one pair proves too diffi-cult to acquire, the sensors canswitch to the alternate pair.However, each observation has alimited total time for acquiringand studying the target. If theacquisition process takes too long,the acquisition logic switches tocoarse-track mode for that obser-vation to acquire the guide stars.

Three basic modes are used totarget a star.

Mode 1 points the Telescope,then transmits a camera image,or spectrographic or photometricpseudo-image, to STOCC.Ground computers make correc-

tions to precisely point theTelescope, and the coordinatespass up through the AdvancedComputer.

Mode 2 uses onboard facilities,processing information from thelarger target apertures, thenaiming the Telescope to place thelight in the chosen apertures.

Mode 3 uses the programmedtarget coordinates in the starcatalog or updated acquisitioninformation to reacquire aprevious target. Called blindpointing, this is used mostly forgeneralized pointing and for theWide Field and Planetary Camera 2,which does not require suchprecise pointing. Mode 3 reliesincreasingly on the updatedguide-star information fromprevious acquisition attempts,stored in the computer system.

HST OPERATIONS

6-6

7-1

very few years, a team of astronauts carries afull manifest of new equipment on the SpaceShuttle for the ultimate “tune-up” in space:

maintaining and upgrading the Hubble SpaceTelescope on orbit.

This ability is one of Hubble’s important features.When the Telescope was being designed, the SpaceShuttle was being readied for its first flights. NASArealized that if a shuttle crew could service HST, itcould be maintained and upgraded indefinitely. Sofrom the beginning,Hubble was designed tobe modular and astro-naut friendly.

The modular designallows NASA to periodi-cally re-equip HST withstate-of-the-art scientificinstruments—giving theTelescope exciting newcapabilities (see Fig. 7-1).In addition to scienceupgrades, the servicingmissions permit astro-nauts to replace limited-life components withsystems incorporatingthe latest technology(see Fig. 7-2).

Cost-Effective Modular Design

The 1993 and 1997 servicing missions increasedHubble’s scientific exposure time efficiencies 11-fold.Astronauts installed two next-generation scientificinstruments, giving the Telescope infrared and ultra-violet vision, and a Solid State Recorder (SSR),further expanding its observing capability.

During Servicing Mission 3B (SM3B), astronauts willadd a camera 10 times more powerful than the

VALUE ADDED: The Benefitsof Servicing Hubble

E

ACS (= 10x WFPC2 in Red)

WFC3 (= 20x NICMOS in IR;35x ACS in NUV)

STIS (= 40x original spectographs)

COS (= 20x STIS)

NICMOS/NCS

SM2 SM3B SM4

WFPC2

SM1

NICMOS

K1175_701

Fig. 7-1Advanced scientificinstrumentsinstalled (orto beinstalled) onHST pave theway to newdiscoveries.

VALUE ADDED: The Benefits of Servicing Hubble

7-2

already extraordinary cameras on board. They also will fit theTelescope with new, super-efficient solar array panels thatwill allow simultaneous opera-tion of scientific instruments.These technologies were notavailable when Hubble wasdesigned and launched.

The following sections identifysome of the planned upgrades toHST and their anticipated bene-fits to performance. Theseimprovements demonstrate thatservicing HST results in signifi-cant new science data at greatlyreduced cost.

Processor

During Servicing Mission 3A(SM3A), astronauts replacedHubble’s original main computer,a DF-224/coprocessor combina-

tion, with a completely newAdvanced Computer based on theIntel 80486 microchip. Thiscomputer is 20 times faster andhas six times as much memory asthe one it replaced (see Fig. 7-3).

In a good example of NASA’sgoal of “faster, better, cheaper,”commercially developed andcommonly available equipment

was used to build the newcomputer at a fraction of thecost of a computer designedspecifically for the spaceflightenvironment.

The new computer’s capabilitieshave increased Hubble’s produc-tivity by performing more workin space and less work on theground. In addition, the

Electrical• Solar Array• SADE

Electrical• SADE

Electrical• VIK

Electrical• S/A33• Diode Box

Electrical• Batteries

Pointing& Control• RSU (2)• MSS (2)• ECU (2)

• Coprocessor

Thermal• MLI patches

• SSAT

Thermal• ASCS• NCS

• ESTR• SSR

• 486• SSR

Pointing& Control• FGS• RWA

Pointing& Control• FGS• RSU (3)

Pointing& Control• FGS• RSU (3)

Thermal• NOBL• SSRF

SM1 SM2 SM3A SM3B SM4

• DIUUpgrade

Maintenance and upgrade

Maintenance

DataManagement

Instrumentation&

Communication

DataManagement

DataManagement

Instrumentation&

Communication

Sys

tem

s

K1175_702

Spacecraft equipment change-outs to enhance mission life, reliability and productivity

Fig. 7-3Processorimprovements

30

25

20

15

10

5

0DF-224Launch

DF-224/COPSM1

No ChangeSM2

HST 486SM3A

Mission

Clo

ck S

pee

d (

MH

z)

K1175_703

Fig. 7-2 Systems maintained and upgraded during each servicing mission


7-3

computer uses a modern programming language,which decreases software maintenance cost.

Data Archiving Rate

The addition of a second SSR during SM3A dramati-cally increased Hubble’s data storage capability. Thescience data archiving rate is more than 10 timesgreater than First Servicing Mission (1993) rates (seeFig. 7-4). Prior to the Second Servicing Mission (SM2in 1997), Hubble used three reel-to-reel taperecorders designed in the 1970s. SM2 astronautsreplaced one of the mechanical recorders with adigital SSR.

Unlike the reel-to-reel recorders, the SSRs have noreels, no tape and no moving parts that can wear out and limit lifetime. Data is stored digitally incomputer-like memory chips until Hubble operatorscommand its playback.

Although an SSR is about the same size and shapeas a reel-to-reel recorder, it can store 10 times asmuch data: 12 gigabits instead of only 1.2 gigabits.This greater storage capacity allows Hubble’ssecond- generation scientific instruments to be fullyproductive.

Detector Technology

Advanced detector technology allows the Telescopeto capture and process faint amounts of light fromthe far reaches of space. Increased power and resolu-tion refinements will enhance Hubble’s performance,delivering even sharper, clearer and more distinctimages.

Adding the Advanced Camera for Surveys duringSM3B will increase the total number of onboardpixels 4800 percent (see Fig. 7-5).

Cryogenic Cooler

Installation of the Near Infrared Camera and MultiObject Spectrograph (NICMOS) Cryogenic Cooler

(NCC) during SM3B will greatlyextend the life of Hubble’s infraredcameras.

NICMOS, which was installed onHubble in 1997, has been a spectacularsuccess. However, in January 1999 itran out of the coolant necessary forconducting scientific operations. Thenew NCC will increase NICMOS’s life-time seven-fold—from 1.8 years to 10years (see Fig. 7-6).

The cost to develop and install theNCC is approximately $21 million,while the cost of NICMOS was $100

million. Installing the cryocooler will preserve andextend the instrument’s unique science contribution,ensuring a greater return on the original investment.

Gig

abit

s/D

ay

ThruSM2

ThruSM2

ThruSM3A

ThruSM4

Service MissionK1175_704

12

10

8

6

4

2

00.6 0.9

3.5

10.4

ThruSM1

ThruSM2

ThruSM3B

ThruSM4

K1175_705

45

40

30

20

10

5

00.89

8.7

27.3

43.2

35

25

15

Nu

mb

er o

f H

ST

Pix

els

(Mill

ion

s)

SM1 SM2 SM3B

K1175_706

0.01.3

10.0

12

10

4

2

0

8

6

Year

s

Servicing Mission

Fig. 7-4 Dataarchiving rateimprovements

Fig. 7-5 Increase in onboard pixels

Fig. 7-6 Increase in HST infrared capability


7-4

Solar Arrays

New, rigid solar arrays installed during SMB3 willprovide substantially more energy to Hubble. Theincreased power will enhance productivity byallowing simultaneous operation of up to fourHubble instruments (see Fig. 7-7).

Simultaneous Science

One of the most exciting advances afforded by serv-icing is the ability to double the simultaneous opera-tions of scientific instruments. Originally, the instru-ments were designed to work in pairs. FollowingSM3B, developments in solar array technology andthermal transport systems will allow four scienceinstruments to operate at the same time, dramaticallyincreasing Hubble’s ability to study the universe (see Fig. 7-8).

SM1 SM2 SM3AK1175_707

SM3B

SI/Cells4200

5100

4900

4300

4100

4700

4500

5300

5500

5700

5900

SI/Cells4550

SI/Cells4550

GA/Cells (Beginning of Life) 5680

So

lar

Arr

ays

Ou

tpu

t P

ow

er

(Min

imu

m W

atts

)

Fig. 7-7 Productivity gains with new solar arrays

SM1 SM2 SM3

K1175_708

2

3

4

5

4

1

0

3

2

Nu

mb

er o

f S

cien

ce In

stru

men

tsA

ble

To

Op

erat

e S

imu

ltan

eou

sly

Service MissionSM4

4

Fig. 7-8 Simultaneous use of science instruments

GLOSSARY

8-1

-A-

Å Angstrom

aberration Property of an optical system that causes an image to have certain

easily recognizable flaws. Aberrations are caused by geometrical factors

such as the shapes of surfaces, their spacing and alignments. Image

problems caused by factors such as scratches or contamination are not

called aberrations.

ACE Actuator Control Electronics

ACS Advanced Camera for Surveys

acquisition, target Orienting the HST line of sight to place incoming target light in an

instrument’s aperture

actuator Small, high-precision, motor-driven device that can adjust the location

and orientation of an optical element in very fine steps, making fine

improvements to the focus of the image

Advanced Computer A 486-based computer that replaced the DF-224 on SM-3A. Performs

onboard computations and handles data and command transmissions

between HST systems and the ground system

AFM Adjustable Fold Mirror

aft Rear of the spacecraft

alignment Process of mounting optical elements and adjusting their positions and

orientations so that light follows exactly the desired path through the

instrument and each optical element performs its function as planned

altitude Height in space

AMA Actuator Mechanism Assembly

AME Actuator Mechanism Electronics

APE Articulating PFR Extender

aperture Opening that allows light to fall onto an instrument’s optics

aplanatic Image corrected everywhere in the field of view

apodizer Masking device that blocks stray light

arcsec A wedge of angle, 1/3600th of 1 degree, in the 360-degree “pie” that

makes up the sky. An arcminute is 60 seconds; a degree is 60 minutes.

ASCS Aft Shroud Cooling System

ASLR Aft Shroud Latch Repair (kits)

ASIPE Axial Scientific Instrument Protective Enclosure

GLOSSARY

8-2

astigmatism Failure of an optical system, such as a lens or a mirror, to image a point

as a single point

astrometry Geometrical relations of the celestial bodies and their real and apparent

motions

ATM Auxiliary Transport Module

attitude Orientation of the spacecraft’s axes relative to Earth

AURA Association of Universities for Research in Astronomy

axial science instruments Four instruments—the STIS, NICMOS, FOC and COSTAR—located

behind the primary mirror. Their long dimensions run parallel to the

optical axis of the HST.

-B-

baffle Material that extracts stray light from an incoming image

BAPS Berthing and Positioning System

BPS BAPS Support Post

-C-C Celsius

Cassegrain Popular design for large, two-mirror reflecting telescopes in which the

primary mirror has a concave parabolic shape and the secondary mirror

has a convex hyperbolic shape. A hole in the primary allows the image

plane to be located behind the large mirror.

CASH Cross Aft Shroud Harness

CAT Crew Aids and Tools

CCC Charge Current Controller

CCD Charge-coupled device

CCS Control Center System

CDI Command data interface

change-out Exchanging a unit on the satellite

cm Centimeter

collimate To straighten or make parallel two light paths

coma Lens aberration that gives an image a “tail”

concave Mirror surface that bends outward to expand an image

GLOSSARY

8-3

convex Mirror surface that bends inward to concentrate on an image

coronograph Device that allows viewing a light object’s corona

COS Cosmic Origins Spectrograph

COSTAR Corrective Optics Space Telescope Axial Replacement

CPL Capillary Pumped Loop

CPM Central Processor Module

CPU Central Processing Unit

CSS Coarse Sun Sensor

CTVC Color television camera

CU/SDF Control Unit/Science Data Formatter

CVL NICMOS Cryo Vent Line

-D-

DBA Solar array Diode Box Assembly

DBC Diode Box Controller

diffraction grating Device that splits light into a spectrum of the component wavelengths

DIU Data Interface Unit

DMS Data Management Subsystem

DMU Data Management Unit

drag, atmospheric Effect of atmosphere that slows a spacecraft and forces its orbit to decay

-E-

ECA Electronic Control Assembly

ECU Electronics Control Unit

electron Small particle of electricity

ellipsoid Surface whose intersection with every plane is an ellipse (or circle)

EPDSU Enhanced Power Distribution and Switching Unit

EPS Electrical Power Subsystem

EP/TCE Electrical Power/Thermal Control Electronics

GLOSSARY

8-4

ESA European Space Agency

ESM Electronics Support Module

E/STR engineering/science data recorders

EVA extravehicular activity

extravehicular Outside the spacecraft; activity in space conducted by suited astronauts

-F-

F Fahrenheit

FGE Fine Guidance Electronics

FGS Fine Guidance Sensor

FHST Fixed Head Star Tracker

FOC Faint Object Camera

focal plane Axis or geometric plane where incoming light is focused by the telescope

FOSR Flexible optical solar reflector

FOV Field of view

FPS Focal plane structure

FPSA Focal plane structure assembly

FRB Fastener retention block

FS Forward Shell

FSIPE FGS Scientific Instrument Protective Enclosure

FSS Flight Support System

-G-

GA Gallium arsenide

G/E Graphite-epoxy

GE General Electric

GGM Gravity Gradient Mode

GSE Ground support equipment

GSFC Goddard Space Flight Center

GLOSSARY

8-5

GSSS Guide Star Selection System

GSTDN Ground Spaceflight Tracking and Data Network

-H-

HGA High Gain Antenna

HRC ACS High Resolution Channel

HST Hubble Space Telescope

hyperboloidal Slightly deeper curve, mathematically, than a parabola; shape of the primary mirror

Hz Hertz (cycles per second)

-I-

IBM International Business Machines Corporation

in. Inch

interstellar Between celestial objects; often refers to matter in space that is not a star,

such as clouds of dust and gas

intravehicular Inside the spacecraft

IOU Input/output unit

IR Infrared

IV Intravehicular

IVA Intravehicular activity

-J-

JPL Jet Propulsion Laboratory

JSC Johnson Space Center

-K-k Kilo (1000)

kB Kilobytes

kg Kilogram

km Kilometer

KSC Kennedy Space Center

GLOSSARY

8-6

-L-

Latch Mechanical device that attaches one component, such as a science

instrument, to the structure of the telescope and holds it in precisely

the right place

LGA Low Gain Antenna

LGA PC Low Gain Antenna Protective Cover

Light-year The distance traveled by light in 1 year, approximately 6 trillion miles

LMSSC Lockheed Martin Space Systems Company

LOPE Large ORU Protective Enclosure

LOS Line of sight

LS Light Shield

luminosity Intensity of a star’s brightness

-M-

m Meter; apparent visual magnitude

M Absolute visual magnitude

µm Micrometer; 1 millionth of a meter

mm Millimeter

MA Multiple access

magnitude, absolute How bright a star appears without any correction made for its distance

magnitude, apparent How bright a star would appear if it were viewed at a standard distance

MAMA Multi-Anode Microchannel Plate Array

MAT Multiple Access Transponder

MCC Mission Control Center

MCP Microchannel plate

metrology Process of making extremely precise measurements of the relative

positions and orientations of the different optical and mechanical

components

MFR Manipulator Foot Restraint

MHz Megahertz

MLI Multi-layer insulation

GLOSSARY

8-7

Mpc Megaparsec (1 million parsecs)

MOPE Multimission ORU Protective Enclosure

MSFC Marshall Space Flight Center

MSM Mode Selection Mechanism

MSS Magnetic Sensing System

MT Magnetic torquer

MTA Metering Truss Assembly

MTS Metering Truss Structure

MULE Multi-Use Lightweight Equipment carrier

-N-

NASA National Aeronautics and Space Administration

NBL Neutral Buoyancy Laboratory at JSC

NASCOM NASA Communications Network

NCC Network Control Center; NICMOS Cryocooler

NCS NICMOS Cooling System

nebula Mass of luminous interstellar dust and gas, often produced after a stellar nova

NICMOS Near Infrared Camera and Multi-Object Spectrometer

nm Nanometers

nmi Nautical miles

NOBL New Outer Blanket Layer

nova Star that suddenly becomes explosively bright

NPE NOBL Protective Enclosure

NSSC-I NASA Standard Spacecraft Computer, Model-I

NT NOBL Transporter

-O-

occultation Eclipsing one body with another

OCE Optical Control Electronics

GLOSSARY

8-8

OCE-EK OCE Enhancement Kit

OCS Optical Control Subsystem

Orientation Position in space relative to Earth

ORU Orbital Replacement Unit

ORUC Orbital Replacement Unit Carrier

OSS Office of Space Science, NASA Headquarters

OTA Optical Telescope Assembly

-P-

PACOR Packet Processing Facility

parallax Change in the apparent relative orientations of objects when viewed

from different positions

parsec A distance equal to 3.26 light-years

PCEA Pointing Control Electronics Assembly

PCS Pointing Control Subsystem

PCU Power Control Unit

PDA Photon Detector Assembly

PDM Primary Deployment Mechanism

PDU Power Distribution Unit

PFR Portable Foot Restraint

photon Unit of electromagnetic energy

PIP Push in-pull out (pin)

pixel Single picture element of a detection device

POCC Payload Operations Control Center

polarity Light magnetized to move along certain planes. Polarimetric observation

studies the light moving along a given plane.

primary mirror Large mirror in a reflecting telescope the size of which determines the

light-gathering power of the instrument

prism Device that breaks light into its composite wavelength spectrum

PSEA Pointing/Safemode Electronics Assembly

PSO HST Project Science Office at GSFC

GLOSSARY

8-9

-Q-

quasar Quasi-stellar object of unknown origin or composition

-R-

RAC Rigid Array Carrier

RAM Random-access memory

radial Perpendicular to a plane (i.e., instruments placed at a 90-degree angle

from the optical axis of the HST)

RBM Radial Bay Module

RDA Rotary Drive Actuator

reboost To boost a satellite back into its original orbit after the orbit has

decayed because of atmospheric drag

reflecting telescope Telescope that uses mirrors to collect and focus incoming light

refracting telescope Telescope that uses lenses to collect and focus light

resolution Ability to discriminate fine detail in data. In an image, resolution refers

to the ability to distinguish two objects very close together in space. In

a spectrum, it is the ability to measure closely separated wavelengths.

resolution, spectral Determines how well closely spaced features in the wavelength

spectrum can be detected

resolution, angular Determines how clearly an instrument forms an image

RF Radio frequency

RGA Rate Gyro Assembly

Ritchey-Chretien A modern optical design for two-mirror reflecting telescopes. It is a

derivative of the Cassegrain concept in which the primary mirror has a

hyperbolic cross section.

RIU Remote Interface Unit

RMGA Retrieval Mode Gyro Assembly

RMS Remote Manipulator System

ROM Read-only memory

RS Reed-Solomon

RSU Rate Sensor Unit

RWA Reaction Wheel Assembly

GLOSSARY

8-10

-S-

SA Solar Array

SAA South Atlantic Anomaly

SAC Second Axial Carrier

SADA Solar Array Drive Assembly

SADE Solar Array Drive Electronics

SADM Solar Array Drive Mechanism

SAGA Solar Array Gain Augmentation

SBA Secondary Baffle Assembly

SBC Single-Board Computer; Solar Blind Channel

SCP Stored Command Processor

SDAS Science Data Analysis Software

SDM Secondary Deployment Mechanism

secondary mirror In a two-mirror reflecting telescope, the secondary mirror sits in front

of the larger primary mirror and reflects light to the point at which it

will be detected and recorded by an instrument. In simple telescopes,

the secondary mirror is flat and bounces the light out the side of the

tube to an eyepiece. In more complex and larger telescopes, it is convex

and reflects light through a hole in the primary mirror.

Servicing Mission NASA’s plan to have the Space Shuttle retrieve the HST and have

astronauts perform repairs and upgrades to equipment in space

SI Science Instrument

SI C&DH SI Control and Data Handling (subsystem)

SIPE Science Instrument Protective Enclosure

SM Secondary Mirror

SMA Secondary Mirror Assembly

SM1 First HST Servicing Mission, December 1993

SM2 Second HST Servicing Mission, February 1997

SM3A HST Servicing Mission 3A, December 1999

SM3B HST Servicing Mission 3B, February 2002

SM4 HST Servicing Mission 4

GLOSSARY

8-11

SOFA Selectable Optical Filter Assembly

SOGS Science Operations Ground System

SOPE Small ORU Protective Enclosure

spectral devices These include spectrographs, instruments that photograph the

spectrum of light within a wavelength range; spectrometers, which

measure the position of spectral lines; and spectrophotometers, which

determine energy distribution in a spectrum.

spectrograph Instrument that breaks light up into its constituent wavelengths and

allows quantitative measurements of intensity to be made

spectrum Wavelength range of light in an image

spherical aberration Image defect caused by a mismatch in the shapes of the reflecting

surfaces of the primary and secondary mirrors. Light from different

annular regions on the primary mirror comes to a focus at different

distances from the secondary mirror, and there is no one position where

all of the light is in focus.

SSAT S-band Single-Access Transmitter

SSC Science Support Center

SSE Space Support Equipment

SSM Support Systems Module

SSM-ES SSM Equipment Section

SSR Solid State Recorder

SSRF Shell/Shield Repair Fabric

STDN Space (flight) Tracking and Data Network

STINT Standard interface

STIS Space Telescope Imaging Spectrograph

STOCC Space Telescope Operations Control Center

STS Space Transportation System

STScI Space Telescope Science Institute

-T-

TA Translation Aids

TAG Two-axis gimbal

TCE Thermal Control Electronics

GLOSSARY

8-12

TCS Thermal Control Subsystem

TDRS Tracking and Data Relay Satellite

TDRSS TDRS System

TECI Thermoelectric-cooled inner (shield)

TECO Thermoelectric-cooled outer (shield)

telemetry Data and commands sent from the spacecraft to ground stations

TLM Telemetry

-U-

UDM Umbilical disconnect mechanism

ULE Ultralow expansion

USA United States Army

USAF United States Air Force

USN United States Navy

UV ultraviolet

-V-

V Volt

V1, V2, V3 HST axes

VCS Vapor-cooled shield

VIK Voltage/Temperature Improvement Kit

-W-

W Watt

Wavelength Spectral range of light in an image

WFC ACS Wide Field Channel

WFPC Wide Field and Planetary Camera. The camera currently in use is the

second-generation instrument WFPC2, installed during the First

Servicing Mission in December 1993. It replaced WFPC1 and was built

with optics to correct for the spherical aberration of the primary mirror.

Advanced Camera for Surveys

SM3B spacewalkers maneuver the AdvancedCamera for Surveys intoposition inside Hubble.

NICMOS Radiator

The SM3B extra-vehicularactivity crew installs anew radiator for the NICMOS Cooling System.

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