nasa facts orbiting geophysical observatory

8/7/2019 NASA Facts Orbiting Geophysical Observatory

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( \ PageNASA F A(T SAn Educational Services Publication of the

National Aeronautics and Space AdministrationVol. II, No . 13

ORBITINGGEOPHYSICAL OBSERVATORY

(P iGES )

(NASA CR OR "tMX OR AD NUMBER' (CATEGO/ fy )

Artist's conception depicts some of the stages of OGO's deployment in space.

The first of a series of large satellites designedto broaden significantly knowledge about theearth and space and how th e sun affects bothwas launched September 4, 1964. The satelliteis called aGO I. aGO is an acronym forQrbiting Qeoprysical Qbservatory.

The approximately half-ton aGO can furnishmany times the data provided by smaller scientific satellites such as Explorers. For exampleOGO I carries 20 different experiments as compared to the_8 experiments of Explorer XVIII. I

However, the principal advantage of aGO i


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Page 2that it makes possible observations of numerousphenomena simultaneously fo r extended periodsof time. 7 Thus, scientists can study in detail theinterrelationships between these phenomena.For example, while some OGO experiments re-port on the erratic behavior of the sun, othersmay describe concurrent fluctuations in earth'sand interplanetary magnetic fields, space radiation, and properties of the earth's atmosphere.

ECCENTRICGEOPHYSICAL OBSERVATORY (EGO)

OGO satellites have tw o basic missions. Inone, OGO is rocketed by an Atlas-Agena boosterfrom Cape Kennedy, Florida, into a highly ec-centric orbit. Typical of this kind of orbit is thatof OGO I which ranges from 175 to 92,827 milesabove earth. When launched into this fa r flyingorbit, OGO may be called EGO, for ~ c c e n t r i c Qeophysical Qbservatory.( EG O traverses earth's space e n v i r o n ~ e n t and

flies beyond it into interplanetary space. Interplanetary space is defined as the region beyondearth's magnetic field.

Some elements of th espace environment andth e orbits ofEGO and POGO(not in scale)

- - - - - - - . . - - - . . . - ~ - -NASA FACTS Vol. II, No. 13IEGO studies the sun, the intense Van Allen

Radiation Region that surrounds earth, the elec-trons and protons constituting the solar wind thatrush constantly from the sun's turbulent surface,the vast shock wave in space created by impactof the speeding solar wind with earth's magneticfield (see NASA Facts-Interplanetary ExplorerSatellites, Vol. II, No. I), and other phenomenanear and at great distances from earth.

EG O reports on both particle and electromagnetic radiation that may peril travelers betweenthe earth and moon. Particle radiation consistsof high energy electrons and protons such asthose constituting the Van Allen Radiation Region.Electromagnetic radiation includes lethal X-rays,gamma rays, and ultraviolet light. These arepart of a family of radiations called the electromagnetic spectrum.

The spectrum is a scale developed by man toclassify radiations that are electrical or magneticin nature and have no mass, or matter. Thefamily includes such harmless (and helpful) mem-bers as visible l ight and radio waves.


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NASA FACTS Vol. II, No . 13POLAR ORBITING

GEOPHYSICAL OBSERVATORY (POGO)In its second basic mission, OGO is launched

by a thrust-augmented Thor-Agena booster fromVandenberg Air Force Base, California, into apolar orbit at altitudes ranging from 150 to 500miles. A satellite in a polar orbit flies in a northand south direction around th e earth . Whenlaunched into a polar orbit, OGO can be calledPOGO for ~ o l a r Q r biting Qeophysical Qbservatory.

The thrust-augmented Thor-Agena has threesolid-propellant rockets providing a total of162,000 pounds of thrust strapped on to its170,000-pound thrust Thor first stage. The resulting 332,000 pounds of thrust is still less thanthe 427,000 pounds of thrust generated by theAtlas booster including its sustainer rockets. AThor-Agena rathe r than th e more powerfulAtlas-Agena can be employed for POGO becauseattaining the POGO orbit requires less energythan achieving the EGO orbit.

A POGO launch from Cape Kennedy is unsuitable because vehicle components that fail to orbitcould fall on inhabited areas. On th e otherhand , a vehicle launched southward from Vandenberg along the Western Test Range fl ies overopen ocean. (EGO is launched into an eastwest orbit.)POGO 's p rimary goal is to increase knowledgeabout how fluctuations in solar activity affect thecharacteristics of earth ' s atmosphere, includingthe ionosphere, and of earth's magnetic field. ]POGO's polar orbit makes the satellite ideal fo rstudy of the auroras {Northern and Southernlights}, the direct entry from time to time of protons and electrons from the sun into the polaratmosphere, and other phenomena that occur

OBSERVATORY SATELLITESOG O Is one of th ree large scientific satellites in theNASA program. Another is th e Orbiting AstronomicalObservatory (OAO) which Is designed to make te lescopic observat ions of th e skies at an a l t i tude freefrom atmospheric Interference. Th e third is th e Ad vanced Orbiting Solar Observatory (AOSO) which willmake an Intensive s tudy fo r a prolonged period of th esu n ' s many phenomena. Forerunners of AOSO are th esmaller Orbiting Solar Observatories launched March 7,1962 and February 3 , 1965. (See NASA Facts-OrbitingSolar Observatory, B-62. )

Page over the fa r northern and far southern areas othe globe.

Since the combination of POGO ' s polar orband the earth ' s rotat ion enables the satellite tcover our entire planet, it ca n make global suveys of many phenomena. Among these arcosmic rays, which are except ionally high energprotons and other atomic particles orig inatinfrom the sun and sources outside of the solar system; electrons and protons in the Van AlleRadiation Reg ion; micro meteoroids, which artiny particles of matter in space; and airglow,feeble light emitted by the earth ' s atmospherat altitudes from about 50 miles to approximatel65 miles.

SPACECRAFT DESCRIPTION

ORBITAL PLANEEXPERIMENT PACKAGEDRIVE ASSEMBLY

VHFOMNIDIRECTIONAL

_ AT"TlTI"'F - C.ONTI"" BOOM

< J ' L A " - ~ A N L ASSEMBLY

r E:XPEFUMEINT BOOMS

ANTENNA BOOM HINGE

EXPERIMENT ANTIENNII---\\

Principal equ ipment of OG O I.OGOs are a series of standardized satellites

Standardized spacecraft are so constructed thadifferent experiments can be installed fo r eacfl ight without redesign of major systems.

OGO's basic systems include a box-like maibody with protruding antennas , panels, anbooms; electrical generation an d sto rag e facilties; apparatus fo r acqu isit ion , storage, antransmittal to earth on command of exper imenta


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Page 4data and i 'nformation on spacecraft operations;automatic orientation equipment; and systemsfor communicating with and controll ing certainoperations on the spacecraft from earth.

At launch, when inside the fairing, or nosecone, of its launch vehicle, OGO resembles arectangular box, 6 feet long by 3 feet square,surrounded by a maze of folded booms, panels,and other appendages. In space, with append-

OGO folded within it s foiring (see text) .

ages deployed, OGO spans about 20 feet acrossit s power-generating solar panels (see below)and almost 50 feet between the fa r ends of itsfront and rear booms . The approximately 1000-pound spacecraft looks like a Gargantuan insect.

Attached to th e solar panels are a total of32,250 solar cells. These cells contain silicon,an element that emits electrons when struck byl ight. Harnessed by wires, the electrons flow aselectric currents that enable the spacecraft tofunction.

Two storage batteries, recharged by the solarpanels, are employed when OGO is in earth ' sshadow. They also supplement the power generated by the solar panels when peak demandsare made on the spacecraft. In addition, thebatteries furnish power from launch until the solarpaddles unfold and function in orbit .

NASA FACTS Vol. II, No. 13

OGO moin body showing mounting of exper iments oninside of door .Many experiments are mounted on the inside

of tw o doors that form part of aGO ' s mainbody. (A n analogy is the storage of items onthe inside door shelves of a refrigerator.) Within the main body are OGO's basic electronic andmechanical systems.

Experiments that must face toward or awayfrom the sun are installed in solar-oriented experimer:"lt packages (SOEP) located on the solarpanels. Those that must be oriented in thedirection OGO is moving are mounted in orbitalplane experiment packages (OPEP). (A satellite's orbital plane may be visualized as animaginary circular or elliptical f lat plate bisectin g the earth. The satellite's orbital path maybe considered the plate ' s edge.) The OPEP'sare located at opposite ends of a rotating shaftat the front of the spacecraft's main body.

Experiments whose functioning would be adversely affected by such influences as electricaland magnetic fields created by instruments inthe spacecraft's main body are mounted in containers at the far ends of booms. Still otherbooms support radio antennas and gas jets.

The jets are part of the system for orientingaGo . Mounting them at the ends of boomstakes advantage of leverage to decrease thequanti ty of propel lant consu med for requiredmotions.


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. - - - - - - ~ ~ ~ ~ - ~ - - - - - - - - - - - ~ NASA FACTS Vol. II, No. 13OGO is equipped with an advanced auto-

matic control s}'stem designed to keep the space-craft's flat rectangular bottom facing earth, itssolar paddles locked on th e sun, and the OPEPoriented in the direction that OGO is moving.Among the principal components of the system

p.. e are horizon sensors which, by detecting infraredradiation (heat) emitted by the earth, can telwhether the craft is properly earth oriented; reaction wheels which, by being accelerated or decelerated, can turn the craft; and th e gas jetnoted earlier.

OG O is readied fo r vibration tes t . This is one of a series of ground tests d es igned to duplicate th e conditions tha t OGO wouldencounter a t launch an d in orbit.


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p a g ~ 6- - - - DATA HANDLINGOGO has th e most advanced data handling

and communications system ever built into aUnited States scientific satellite. Either of itstw o tape recorders ca n record data at a rate asmuch as 4000 bits (units of information) per second. Together, the recorders can accumulate86 million bits. The tape recorder system cantransmit its data to earth at speeds as high as128,000 bits per second.

Tracking and obtaining data from OGO is performed by NASA's global Space Tracking andData Acquisition Network (ST ADAN) of groundstations .

85- foo t d iameter an tenna of Space Tracking and Data Acquisition Network stat ion a t Rosman, N.C. (For size comparison,

note automobile in backgraund . )

STADAN funnels all data to NASA's GoddardSpace Flight Center, Greenbelt, Maryland.The computers at th e OGO Control Center an dat the Data Processing Center, both located atGoddard, sort the data and prepare it for use byindividual OGO experimenters an d OGO's operation personnel. The experimenters have exclusive use of OGO scientific data for a year .

NASA FACTS Vol. II, No. 13Afterwards, the information is made availableto the world scientific community .

Commands for performance of certain OGOfunctions are determined at th e OGO ControlCenter and transmitted to STADAN stations. Attw o of these stations, Rosman, N.C., and Fairbanks, Alaska, huge 85-foot diameter antennasbeam the commands to the spacecraft.

Aiding control of OGO from earth is realtime communication between the Control Centerat Goddard and OGO via the Rosman station.This is provided by a direct microwave radio linkbetween Goddard and Rosman.

Real time: reporting on or recording of events simul -taneously with the events. '.

LONG-RANGE TREATMENT SAVES OGO I

Atlas-Agena baoster launches OGO I.

In th e early days of the Space Age, a malfunctioning satellite was lost to science. Today,ways can sometimes be found to override a defect and derive significant benefit from the spacecraft. This is the case with OGO I. Amongthe factors which aided in saving OGO I forscience is its greater capability for being commanded from earth and the better diagnostic dataavailable from the spacecraft. These were madepossible by the satellite ' s size, weight, andpower.

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