2.11 EXTRAVEHICULAR ACTIVITY(EVA)

CONTENTS

Description ........................................... 2.11-1Extravehicular Mobility Unit ............. 2.11-2Airlock .................................................. 2.11-11EVA Support Equipment ................... 2.11-15Simplified Aid for EVA Rescue ......... 2.11-17Operations ............................................ 2.11-19EVA Summary Data............................ 2.11-22EVA Rules of Thumb .......................... 2.11-22

Description

An EVA occurs when a crewmember leaves theprotective environment of a spacecraft's pres-surized cabin and ventures out into the vacuumof space wearing a space suit. An EVA is com-monly referred to as a spacewalk. The currentspace suit, designed for a total maximum dura-tion of 7 hours, provides environmental protec-tion, mobility, life support, and communica-tions. Two suits are included in each baseline

orbiter mission, and consumables are providedfor three two-person, 6-hour EVAs. Two EVAsare available for payload use, with the thirdreserved for orbiter contingency operations.EVA has been demonstrated to be useful insatellite repair, retrieval, and refueling as wellas with space station development.

There are three basic categories of EVA:scheduled, unscheduled, and contingency. Ascheduled EVA is defined as any EVA incorpo-rated into the nominal flight plan in order tocomplete a specific mission objective. Anunscheduled EVA is not part of the flight plan;rather, it is conducted to achieve payload opera-tion success or to advance overall missionaccomplishments. A contingency EVA is alsounscheduled, but is required to ensure safereturn of the orbiter and flight crew.

A subcategory of scheduled EVA is the quick-response EVA. A quick-response EVA must beperformed within a few hours after a problem isdiscovered, and it is usually associated withpayload deployment. Quick-response EVAs areplanned pre-flight, and the crew prepares forthe EVA even though it may not be performed.

Mission Date Purpose of EVA EVA crew No. EVA/mission

Duration,man-hours

STS-6 Apr 4-9, 83 System Functional Demo Musgrave/Peterson 1 8 hr, 34 minSTS-41B Feb 3-11, 84 MMU Capability Demo NcCandless/Stewart 2 23 hr, 14 minSTS-41C Apr 6-13. 84 Solar Max Satellite Repair Van Hoften/Nelson 2 20 hr, 12 minSTS-41G Oct 5-13, 84 Orbiter Fuel Transfer Demo Leestma/Sullivan 1 6 hr, 58 minSTS-51A Nov 8-16, 84 Westar/Palapa Satellite Retrieval Allen/Gardner 2 24 hr, 28 minSTS-51D Apr 12-19, 85 Syncome F3 Satellite Repair Griggs/Hoffman 1 6 hr, 20 minSTS-51I Aug 27-Sep 3, 85 Syncome F3 Satellite Repair Fisher/Van Hoften 2 23 hr, 42 minSTS-61B Nov 26-Dec 3, 85 Large Structure Assembly Spring/Ross 2 24 hr, 40 minSTS-37 Apr 5-10, 91 GRO Satellite Repair/Locomotion Studies Ross/Apt 2 20 hr, 58 minSTS-49 May 10-14, 92 Intelsat Repair and Assembly of Station by

EVA Methods (ASEM)Thuot, Hieb, Akers,Hornton,

4 59 hr, 51 min

STS-54 Jan 17, 93 First EVA Detailed Test Objective (DTO1210)

Harbaugh, Runco 1 8 hr, 56 min

STS-57 Jun 25, 93 EURECA Antenna Stow and Second EVADTO (1210)

Low, Wisoff 1 11 hr, 40 min

STS-51 Sep 16, 93 Third EVA DTO (1210) Walz, Newman 1 14 hr, 10 minSTS-61 Dec 4-8, 93 Hubble Space Telescope Repair Mission Musgrave, Hoffman,

Akers, Thornton5 70 hr, 58 min

STS-64 Sep 16, 94 SAFER First Flight Lee, Meade 1 13 hr, 42 minSTS-63 Feb 9, 95 First EVA Development Flight Test (EDFT)

(Spartan Mass Handling)Foale, Harris 1 13 hr, 18 min

STS-69 Sept 16, 95 Second EDFT (Task board with station EVAinterfaces)

Voss, Gernhardt 1 13 hr, 32 min

STS-72 Jan 14-16, 95 Third EDFT (Station assembly andmaintenance hardware)

Chiao, Barry, Scott 2 26 hr, 4 min

STS-76 Mar 27, 96 Fourth EDFT (MEEP - Mir EnvironmentalEffects Payload)

Godwin, Clifford 1 12 hr, 4 min

Space Shuttle EVA Chronology

Extravehicular Mobility Unit

Extravehicular activities are classified accordingto level of complexity: simple, intermediate, orcomplex. A simple payload EVA requires mini-mal unique tools, mockups, or mobility aids.Existing procedures and techniques may beadapted to particular EVA needs, thus requiringminimal crew training. An intermediate pay-load EVA requires development of new toolsand equipment. Some procedure and techniquedevelopment is required, with more extensivetraining necessary. A complex payload EVArequires the design and development of com-plex or elaborate tools and equipment. Thetasks require extension of basic capabilities and

may pose difficulty in access or restraint. Proce-dure and technique development is extensive, asare crew training requirements.

Extravehicular Mobility Unit

The extravehicular mobility unit (EMU) is anindependent anthropomorphic system that pro-vides environmental protection, mobility, lifesupport, and communications for the crewmem-ber to perform EVA in Earth orbit. For EMUdesign considerations, an EVA is defined as anytime the EMU external environmental pressureis below 4.0 psia. The EMU is designed to

accommodate an EVA mission with a totalmaximum duration of 7 hours, consisting of 15minutes for egress, 6 hours for useful EVAtasks, 15 minutes for ingress, and a 30-minutereserve. The EMU also accommodates specificmetabolic rate limits, including (1) an averagemetabolic rate not exceeding 1600 Btu/hr in anygiven EVA hour and not exceeding 1000 Btu/hrfor the entire duration, (2) a peak metabolic ratenot exceeding 2000 Btu/hr for a period of 15minutes, and (3) a minimum metabolic rate notless than 400 Btu/hr for a period of 30 minutes.The EMU is an integrated assembly, primarilycomposed of the space suit assembly, lifesupport system, and numerous items of associ-ated support and ancillary equipment.

Space Suit Assembly

The space suit assembly (SSA) is the anthro-pomorphic pressure vessel that encloses thecrewmember's torso, limbs, and head. The SSAprovides a variety of functions while thecrewmember performs an EVA, including suitpressure retention, crewmember mobility, crew-member liquid cooling distribution, oxygenventilation gas circulation, downlink of crew-member's electrocardiogram data via EMUradio, crewmember interface with EMU radio,crewmember in-suit drinking water, and urinecontainment. The SSA operates under specificpressure requirements and leakage criteria.

The space suit assembly consists of thefollowing:

Hard upper torso/arms

Lower torso assembly

Extravehicular gloves

Helmet/extravehicular visor assembly

Liquid cooling and ventilation garment

Operational bioinstrumentation system

Communications carrier assembly

In-suit drink bag

Urine collection device

Maximum absorption garment.

The hard upper torso (HUT) provides pressurecontainment for the upper torso as well as beingthe central component from which the mechani-cal, electrical, and fluid interfaces of the EMUbranch. The HUT is available in four sizes toaccommodate 5th through 95th percentile-sizedcrewmembers. The planar HUT, which deletesthe arm gimbal and bellows assembly, will beavailable in two sizes. The HUT includes thefollowing components: fiberglass shell (withwater tubes and oxygen ducts), assortedmounting brackets, waterline and vent tubeassembly, multiple water connector, EMUelectrical harness, shoulder bearing assemblies,waist disconnect ring (passive half), helmetdisconnect ring, and thermal micrometeoroidgarment (TMG). The right and left arm assem-blies are flexible, anthropomorphic pressurevessels that encompass the arms. Each armassembly includes the following components:upper arm assembly, rotating scye bearing,lower arm assembly, rotating arm bearing, wristdisconnect ring, urethane pressure bladders,cloth restraint systems, and TMGs for the upperand lower arm assemblies.

The lower torso assembly (LTA) consists of aflexible anthropomorphic pressure vessel thatencompasses the waist, lower torso, legs, andfeet. The LTA includes the following compo-nents: waist assembly, waist disconnect ring,trouser assembly, rotating waist bearingbetween the waist and trouser assemblies, bootassembly, urethane pressure bladders, clothrestraint systems, and TMGs for the waist,trouser, and boot assemblies.

The current sizing of the arm/leg assemblies isaccomplished on the ground using differentsizes of each assembly for a particular crew-member. An enhanced EMU has been devel-oped to provide an on-orbit capability of EMUresizing by using various arm/leg segments andsizing rings. The on-orbit quick-sizing capabil-ity, uses threaded quick-disconnects, softgoodsizing elements, aluminum sizing rings, andadjustable-length restraint lines. This suit incor-porates dual lip seal mobility bearings and low-torque fabric joints. The enhanced EMU willphase out the current space suit for futurestation and shuttle operations.

SSA Arm Assembly

Lower Torso Assembly with TMG Removed

The extravehicular gloves consist of a detach-able, flexible pressure vessel, encompassingeach hand for use during EVA. The extrave-hicular gloves include the following compo-nents: urethane pressure bladder and clothrestraint system, wrist disconnect ring withrotating wrist bearing, wrist gimbal ring,adjustable palm restraint bar/strap, wrist tetherstrap, and TMG with palm restraint bar. Thecurrent 4000 series gloves incorporate a stan-dard nine-size system to size the gloves for acomfortable fit. The glove fingers use a sizingfeature that consists of a pair of polyesterdacron cords to provide finger length adjust-ments. Customized gloves can be manufacturedfor the crewmember if a proper fit cannot beobtained from the standard size glove.

Enhanced Arm Assembly

The helmet, a "one-size-fits-all" model, consistsof a detachable, transparent, hard pressurevessel encompassing the head. The helmetincludes the following components: hard trans-parent bubble, helmet disconnect ring, helmetpurge valve, and vent pad. Two crew optionalitems are also available for the helmet. One ofthese items is the Fresnel lens, which is mountedto the lower front inside of the helmet toimprove display control module visibility forthe crewmember. The other item is the valsalvadevice, attached to the inside of the bubble,which allows the crewmember to clear his or herears during pressure changes. The extravehicu-lar visor assembly (EVVA) attaches to thehelmet to provide the crewmember with visual,

thermal, impact, and micrometeoroid protec-tion. The EVVA includes the following compo-nents: clear protective visor, sun visor, centerand side eyeshades, fiberglass shell, and latchmechanisms and supporting structure for thevisor and eyeshades.

Enhanced Lower Torso Assembly

The liquid cooling and ventilation garment(LCVG) is a form-fitting elastic garment wornagainst the crewmember's body. The LCVGincludes the following components: outerrestraint fabric, inner liner assembly, crewoptional comfort pads, biomed pocket, dosime-ter pocket, water tubing network, paramanifoldassembly, ventilation ducting network, ventplenum assembly, multiple water connector,and full torso zipper. The garment supports anetwork of tubing that circulates water over thebody to provide cooling to the crewmember. Italso supports a network of ducting that drawsventilation gas from the suit extremities androutes it back to the primary life support systemto complete the suit ventilation loop. Connec-tions to the ducting in the HUT for both coolingwater and ventilation flow are made at theLCVG half of the multiple water connector. TheLCVG is sized to fit the crewmember based on asizing system with six size ranges.

The communications carrier assembly (CCA) isa cloth aviator-type cap that positions andsupports the electronics for interface with theEMU radio for crewmember communications.The CCA contains the microphones and ear-phones necessary for the EVA crewmembers tocommunicate with each other or with theorbiter. The CCA also allows the EVA crew-members to talk to Mission Control via theorbiter communications system. Six sizes allowthe CCA to fit 5th through 95th percentile-sizedcrewmembers. The CCA includes the followingcomponents: skull cap, ear cups, ear phones, earseals, microphone modules, microphone booms,summing module, interconnect wiring, interfacecable, neck strap, crew-optional chin strap, andperspiration absorption strap.

The in-suit drink bag is a dielectrically sealedbag assembly attached to the interior of theHUT that supplies drinking water to thecrewmember during EVA. The drink bag isavailable in two sizes with the capacity for 21 or32 fluid ounces of water. The in-suit drink bagincludes the following components: bladder,inlet valve, drink valve, drink tube, and velcroattachments.

The urine collection device (UCD) is adisposable, flexible container that has thecapacity to hold up to 32 fluid ounces of urine.The UCD is worn under the LCVG by malecrewmembers during EVA. It is designed forone-time use, then disposed of as wet trash. TheUCD includes the following components:collection bag, attachment straps, one-waycheck valve, and disposable roll-on cuff.

The maximum absorption garment (MAG)consists of multiple layers of material designedto rapidly absorb and store urine. The MAG isdesigned to be worn under the LCVG by maleor female crewmembers during EVA. It has thecapacity to hold 32 fluid ounces of urine and isdisposable after use. The MAG includes thefollowing components, multilayer absorbentmaterial and tape attachment straps.

Life Support System

The life support system (LSS) provides a safeliving environment inside the EMU. The LSSprovides a variety of functions while the crew-member performs an EVA, including provision

of breathing oxygen, suit pressurization, crew-member cooling, crewmember communications,displays and controls for crewmember opera-tion of the EMU, and monitoring of EMUconsumables and operational integrity. The lifesupport system consists of the following:

Primary oxygen system

Secondary oxygen pack

Oxygen ventilation circuit

Liquid transport system

Feedwater circuit

Electrical interfaces

Extravehicular communicator (EMU radio)

Display and control module

Caution and warning system.

The primary oxygen system, oxygen ventilationcircuit, liquid transport system, feedwatercircuit, electrical interfaces, extravehicular com-municator, and the caution and warning systemmake up the primary life support subsystem(PLSS). The secondary oxygen pack is aseparate unit that is attached to the bottom ofthe PLSS. Together, the PLSS and the secondaryoxygen pack make up the backpack of the EMU.

The primary oxygen system provides acrewmember with breathing oxygen andsatisfies pressure requirements for EVA. Thesystem stores 1.217 pounds of oxygen at 850psia and 90 F. It delivers oxygen during EVAat 4.3 0.1 psid, and maintains a metabolic userate range of 0.02 to 0.33 lb/hr. The system ischarged through a common multiple connectionto the orbiter environmental control and lifesupport system. Charging pressure is 850 50psig. The minimum usable pressure is 60 psi.The system performs various functions,including suit pressurization, provision ofbreathing oxygen, and water pressurization.The primary oxygen system includes thefollowing components: oxygen tanks, oxygentank pressure sensor, flow limiter, oxygenshutoff valve, oxygen actuator, suit pressureregulator, water pressure regulator, high moderelief valve, and low mode relief valve.

The secondary oxygen system, also known asthe secondary oxygen pack (SOP), is the backupassembly to the primary oxygen system. Thisbackup system provides a minimum of 30minutes of emergency oxygen in the purgemode. The SOP functions include suit pressuri-zation, provision of breathing oxygen, and somedegree of cooling in the purge mode. There isno required crewmember interface to activatethe SOP; it automatically activates whenever theoxygen actuator is in the EVA position and suitpressure is less than 3.9 psid. The SOP includestwo oxygen tanks, containing a total of 2.65pounds of oxygen at 5800 psia and 70 F. Thesystem includes the following components:oxygen tanks, SOP inlet pressure gauge, first-stage regulator, interstage gauge, second-stageregulator/shutoff valve/flow restrictor, PLSS/SOP interface connector, and oxygen tankpressure sensor.

The oxygen ventilation circuit forms a closedloop with the space suit assembly. The circuitprovides oxygen for breathing, suit pressuriza-tion for intravehicular activity (IVA) and EVAoperation, and ventilation for cooling andelimination of exhaled gases. The oxygen flowpicks up heat, humidity, carbon dioxide, andother contaminants, which are removed fromthe EMU by the ventilation circuit components.The system includes the following components:fan/water separator, slurper/ sublimator, vent

flow sensor/backflow check valve, suit pressuresensor, suit pressure gauge, contaminant control(lithium hydroxide) cartridge (CCC), carbondioxide sensor, display control module purgevalve, helmet purge valve, positive pressurerelief valve, negative pressure relief valve, SOPcheckout package, muffler, and SOP checkoutfixture. Ventilation flow is picked up at thebody extremities and returned to the uppertorso via a vent duct manifold that is part of theLCVG. From the upper torso, the gas is routedback into the PLSS and the CCC. The CCC issized to absorb 1.48 pounds of carbon dioxideassociated with 7000 Btu of metabolic activityover a 7-hour EVA period. The cartridge isinstalled in the back of the PLSS and isreplaceable on orbit. On the ground, the usedcartridge can be recharged for future use.

The liquid transport system uses the centrifugalpump to circulate approximately 240 lb/hr ofwater through the LCVG. The function servedby the liquid transport system is to providecooling to the crewmember. The system in-cludes the following components: pump, tem-perature control valve, LCVG, gas trap, pumppriming valve, pump check valve, sublimatortemperature sensor, and service and coolingumbilical bypass valve. During IVA operation,the pump circulates water not only through theEMU, but also through the service and coolingumbilical to the orbiter heat exchanger.

Secondary Oxygen Pack

LiOH Cartridge

The feedwater circuit contains the equipmentand water to dissipate heat loads imposed onthe system by the crewmember, the PLSS, andthe environment. It also contains equipment toremove moisture from the ventilation circuitand gas from the transport circuit, to separatethe water and gas, and to put them back in theirrespective loops. The feedwater circuit func-tions involve heat rejection, LCVG watermakeup, and vent loop condensate separationand storage. The system includes the followingcomponents: feedwater tanks (2 primary/1reserve), feedwater tank pressure sensors,reserve feedwater tank check valve, feedwaterpressure regulator, feedwater shutoff valve,feedwater pressure sensor, sublimator, feed-water relief valve, condensate water relief valve,water separator, and coolant isolation valve.The primary and reserve tanks store approxi-mately 10 pounds of feedwater at 15 psig. Thereserve feedwater tank provides 30 minutes ofwater for EMU cooling in the event that primaryfeedwater is depleted. Potable water from theorbiter ECLSS is used to fill or recharge the tanks.

The EMU electrical system is composed of thefollowing main components: battery, feedwatershutoff valve, coolant isolation valve, motor,instrumentation, extravehicular communicator,

display and control module, and caution andwarning system. Electrical interfaces existbetween the display and control module andparts of the PLSS, SOP, and C/W. The powersupply for operation of all electrical componentsof the EMU is a battery installed in the back of thePLSS. The EMU battery consists of eleven sealed,silver-zinc, high current density cells connected inseries. The battery provides a minimum of 26.6amp-hr of power over a 7-hour EVA mission at anominal voltage of 16.5 V dc.

The extravehicular communicator (EVC) iscomposed of two parts, the orbiter-based equip-ment and the EMU-based equipment. Theorbiter equipment consists of the EVA/airtraffic control transceivers and antennas. Thisconfiguration provides communication with theEVA crewmembers and relay between EVAcrewmembers and the ground (including down-link ECG and real-time data system (RTDS)telemetry). The EMU equipment consists of theEMU radio and antenna. It provides voicecommunications with other EVA crewmembersand the orbiter, ECG/RTDS telemetry to theorbiter for recording and/or downlink, andcaution and warning tones to alert the EVAcrewmember of anomalies or other significantevents. The EVC includes the following compo-

nents: orbiter UHF system, EMU radio, EMUelectrical harness, communications carrierassembly, biomed sensors, COMM MODE selec-tor switch, COMM switch, volume controls, andreal-time data system. Orbiter panels O6, A1R,and R10 are the crew communication interfaces.The panels control UHF operation, air-to-air orground transmission, and biomed data down-link/recording respectively.

The display and control module (DCM) containsall controls and displays necessary for nominaloperation and monitoring of EMU systems. TheDCM includes the following components:POWER mode switch, DISPL switch, FANswitch, COMM switch, communications volumecontrols, display intensity control, oxygenactuator, temperature control valve, pressuregauge, DCM purge valve, alphanumeric displayCOMM mode selector, and WATER switch. TheDCM is installed on the hard upper torso, withthe surfaces covered with a TMG. This TMGcontains the labels for the controls and displays.

The EMU caution and warning system (CWS)consists of instrumentation and a microprocessorto obtain, process, and visually displayinformation for use by the EVA crewmember inthe operation and management of the EMU. Thesystem contains built-in test equipment (BITE),consisting of software and hardware that verifyproper CWS operation. CWS serial data are alsorouted to the ground by the real-time datasystem. The CWS functions involve displayingEMU leak check procedures, monitoring anddisplaying EMU consumables status, monitoringEMU operational integrity, and alertingcrewmembers to EMU anomalies. The systemincludes the following components:alphanumeric display with BITE indicator, dis-play (DISPL) switch, alert/status/warning tones,sensors, and "black box" processor. The CWSreceives inputs from EMU sensors and from theDISPL switch located on the DCM. Sensors gatherinformation throughout the EMU system and relayit to the CWS. Information is provided onpressures, temperatures, currents, and voltages.

Display and Control Module

EMU Ancillary Equipment

The EMU ancillary equipment consists ofhardware necessary to support the EMU duringall phases of EVA (prep/post/operation). Thefollowing list itemizes the components with abrief description of their functions.

EMU helmet lights - attach to the helmet EVVAand provide two functionally independent sets oflights for portable lighting during an EVA task.

EMU scissors - steel cutters with one serratededge capable of cutting anything from fabricbags and straps to lightweight steel cable andKevlar cord.

EMU wrist mirror - attaches to the wrist of theEVA glove to allow the EVA crewmember toview the controls and displays on the front ofthe EMU.

EVA cuff checklist - a set of reference cardsbound by an aluminum alloy bracket attachedto a wrist band. The reference cards, approxi-mately 4 inches by 5 inches in size, containprocedures and reference data for performingEVA tasks and for aiding in the diagnosis andresolution of EMU malfunctions.

Food stick - a fruit bar contained in an ediblewrapper, positioned just above the neck ringadjacent to the drink valve on the in-suit drinkbag.

In-suit drink bag syringe - a device used toremove gas from the water in the drink bag.The needle of the syringe is inserted in the inletvalve of the bag, and gas is suctioned out of thebag with the syringe.

Thermal mittens - an adjustable enclosurecomposed of several layers of thermal blanketsand aluminized Mylar with a layer of Nomexfelt on the palm and undersides of the fingersthat fit conformally around the EV gloves toprovide greater thermal hand protection atextreme high and low temperature worksites.

Lower torso assembly donning handles - left andright handles that aid in the mating of the hardupper torso and lower torso assembly halves ofthe waist ring.

Contingency tool - a pry bar used to disconnectthe LTA and HUT halves of the waist ring in theevent that the latching mechanism becomesjammed. Operation of the pry bar may damagethe latching mechanism; therefore, it should beused only if the waist ring becomes jammed andthe crewmember is entrapped in the space suit.

Bends treatment adapter (BTA) - an emergencydevice that may be used on-orbit in the event anEVA crewmember contracts decompressionsickness (bends). The BTA converts the EMUinto a hyperbaric treatment chamber, pressuriz-ing the EMU to 8.0 psid over ambient cabinpressure.

SOP checkout fixture - a flight support test iteminstalled on the HUT half of the neck ringduring pre-EVA operations.

DCM plug - a cover that attaches to the multipleconnector on the DCM in the event that waterbegins leaking from the connector after theservice and cooling umbilical multiple connectoris removed.

Prep kit - items necessary for preparing the EMUfor EVA, such as antifog wipes, tissue-typewipes, scissors, and urine collection deviceclamps.

Maintenance kit - additional equipment neces-sary for routine EMU maintenance, includingvalsalva devices, stericide wipes, lubricantwipes, antifog wipes, and urine collectiondevice roll-on cuffs.

Bio kit - equipment associated with the biomedinstrumentation, including EVA cables, over-tapes, electrode placement illustration, alcoholwipes, stoma seals, and electrode paste.

Airlock stowage bag - a Nomex bag used fortemporary storage and transfer of items used inprep- and post-EVA operations. When stowedin the airlock over the inner hatch, the bag andits contents are removed from the airlock priorto airlock depressurization.

EVA bag - used to stow various items (camera,thermal mittens, tool caddy) in the airlock forpossible use during EVA. The EVA bag remainsin the airlock during the EVA.

Airlock

An airlock on the orbiter accommodatesastronaut EVA operations. The airlock permitsEVA crewmembers to transfer from the mid-deck crew compartment into the payload bay inEMUs, without depressuring the orbiter crewcabin. The internal airlock provides launch andentry stowage of up to four EMUs, while theexternal airlock can stow two EMUs. Both typesof airlock contain the interfaces and associateddisplays and controls for the orbiter systemsthat support EMU operation and servicing.Sized to accommodate a two-person EVA, theinternal airlock dimensions have a diameter of63 inches, a length of 83 inches, and twoD-shaped 40-inch-diameter openings (three forexternal airlock). The internal airlock's volumemeasures 150 cubic feet, while the externalairlock has a volume of 185 cubic feet. Supportfunctions performed in the airlock includedepressurization and repressurization, EVAequipment recharge, LCVG water cooling, andEVA equipment checkout, donning, andcommunications. All EVA gear, checkout panel,and recharge stations are located against theinternal walls of the airlock.

Airlock Hatches

Two pressure-sealing hatches are mounted on theinternal airlock, while the external airlockcontains three of these hatches. The inner hatch islocated on the exterior of the airlock opening intothe middeck. The inner hatch isolates the airlockfrom the crew cabin. The outer hatch isolates theairlock from the unpressurized payload baywhen closed and permits the EVA crewmembersto exit from the airlock to the payload bay whenopen. The external airlock's third hatch is anadditional upper, outer hatch that will be usedfor docking operations. Each hatch has sixinterconnected latches with gearbox and actuator,a window, a hinge mechanism with hold-opendevice, a differential pressure gauge on each side,and two equalization valves.

Airlock repressurization is controlled from themiddeck or inside the airlock. It is performedby equalizing the airlock and cabin pressurewith airlock-hatch-mounted equalization valveson the inner hatch. Depressurization of the air-lock is controlled from inside the airlock. Theairlock is depressurized by venting the airlock

pressure overboard. The two D-shaped airlockhatches are installed to open toward the pri-mary pressure source, the orbiter crew cabin, toachieve pressure-assist sealing when closed.Each hatch opening is 40 inches in diameter, yetwith one side being flat, the minimum dimen-sion is 36 inches.

The 4-inch-diameter window in each airlockhatch is used for crew observation from thecabin to the airlock and the airlock to thepayload bay. The dual window panes are madeof polycarbonate plastic and are mounted di-rectly to the hatch using bolts fastened throughthe panes. Each airlock hatch has dual pressureseals to maintain the airlock's pressure integrity.One seal is mounted on the airlock hatch andthe other on the airlock structure. A leak checkquick disconnect is installed between the hatchand the airlock pressure seals to verify hatchpressure integrity before flight.

Each airlock hatch has the following designcharacteristics: (1) capable of being fullylocked/unlocked from either side, (2) designedfor 2000 open/close cycles, (3) one-handedoperation by astronaut in pressure suit, (4)capable of opening against 0.2 psid maximum, (5)latches capable of withstanding 20 g's in the +Xdirection, and (6) actuator handle load of 30pounds maximum.

The gearbox with latch mechanisms on eachhatch allows the flight crew to open or close thehatch during transfers and EVA operations. Thegearbox and the latches are mounted on thelow-pressure side of each hatch, with a gearboxhandle installed on both sides to permit opera-tion from either side of the hatch. Three of thesix latches on each hatch are double-acting withcam surfaces that force the sealing surfacesapart when the latches are opened, therebyacting as crew-assist devices. To latch orunlatch the hatch, the gearbox handle must berotated 440.

The hatch actuator/gearbox is used to providethe mechanical advantage to open and close thelatches. The hatch actuator lock lever requires aforce of 8 to 10 pounds through an angle of 180to unlatch the actuator. A minimum rotation of440 with a maximum force of 30 poundsapplied to the actuator handle is required tooperate the latches to their fully unlatchedpositions.

Airlock in Middeck External Airlock(port side view)

External Airlock ISS Configuration(planned for OV-103, OV-104, OV-105)

Airlock Repressurization, Schematic Diagram

The hinge mechanism for each hatch permits aminimum opening sweep into the airlock or thecrew cabin middeck.

The inner hatch of the internal airlock (airlock tocrew cabin) is pulled or pushed forward to thecrew cabin approximately 6 inches. The hatchpivots up and to the right side. Positive locksare provided to hold the hatch in both anintermediate and a full-open position. Theouter hatch of the internal airlock (airlock topayload bay) opens and closes to the contour ofthe airlock wall. The hatch is hinged to bepulled first into the airlock and then forward atthe bottom and rotated down until it rests withthe low-pressure (outer) side facing the airlockceiling (middeck floor). The hatch has a hold-open hook that snaps into place over a flangewhen the hatch is fully open. To support andprotect the hatch against the airlock ceiling, thehatch incorporates two deployable struts.

The configuration of the external airlock,planned for International Space Station (ISS)operations, contains an inner hatch, an EVhatch, and a docking hatch. The inner hatch ofthe external airlock (airlock to crew cabin mid-deck) has the same opening mechanism as theouter hatch of the internal airlock. The hatch ishinged so that it can be pulled into the middeckand rotated down until it rests on the middeckfloor. The EV hatch of the external airlock(airlock to payload bay) also opens in the samemanner. The docking hatch, located on the floorof the external airlock (toward the payload baydoors), is hinged to be pulled into the airlockand then rotated until the low pressure siderests against the airlock wall facing toward thenose of the orbiter. The external airlock hatchesalso have hold-open protection and deployablestruts for support against the airlock structure.

Airlock Hatch Latches, Schematic Diagram

Airlock in middeckTunnel adapter

Aft hatch

Upper hatch forextravehicularactivity operations

X0 576.00bulkhead

PressurizedCrew

Compartment

Forwardfuselage

Tunnel adapter provides Shirt-sleeve passage

to Spacelab EVA capability (with a irlock)

SpacelabPressurize

Module

444.cvs

Airlock/Tunnel Adapter

Airlock Subsystems

The airlock air circulation system providesconditioned air to the airlock during non-EVAperiods. The airlock revitalization system ductis attached to the outside airlock wall at launch.Upon airlock hatch opening in flight, the duct isrotated by the flight crew through thecabin/airlock hatch and installed in the airlock.The duct has a removable air diffuser cap,installed on the end of the flexible duct, whichcan adjust the air flow from 216 pounds perhour. The duct must be rotated out of theairlock before the cabin/airlock hatch is closedfor chamber depressurization. During the EVApreparation period, the duct is rotated out of theairlock and can be used for supplemental aircirculation in the middeck.

To assist the crewmember before and after EVAoperations, the airlock incorporates handrailsand foot restraints. Handrails are locatedalongside the avionics and ECLSS panels, withaluminum alloy handholds mounted on eachside of the hatches. Each handrail has aclearance of 2.25 inches between the airlock walland the handrail to allow crewmembers to gripit while wearing a pressurized glove. Footrestraints, sized for the EMU boot, can beinstalled on the airlock floor nearer the payloadbay side. The ceiling handhold is installednearer the cabin side of the airlock. A rotationrelease knob on the foot restraint is designed forshirt-sleeve operation and, therefore, must bepositioned before the suit is donned. The footrestraint is bolted to the floor and cannot beremoved in flight.

Airlock-based EMU support componentsprovide for EMU stowage, EMU operationalsupport, and EMU recharge during intravehicu-lar activity operations. These componentsinclude the EMU mount, the service and coolingumbilical, and the lower torso restraint bag. TheEMU mount provides a mechanical interfacebetween the EMU and airlock wall for EMUstowage. The mount attaches to the back side ofthe EMU and engages with three fixtures on thewall of the airlock. The mount is also used tomaintain the EMU in a fixed position on orbitfor EMU donning and doffing operations. Ifnecessary, the EMU mount can be removedfrom the airlock wall while on orbit.

The service and cooling umbilical consists ofthree water hoses, a high pressure oxygen hose,electrical wiring, water pressure regulators, anda strain relief tether. The system is used tointerconnect the EMU and the orbiter airlock fortwo major functions: electrical power, hardlinecommunications, oxygen supply, wastewaterdrainage, and water cooling capability from theorbiter during IVA operation; and rechargecapability for the PLSS oxygen tanks, waterreservoir, and battery.

The lower torso restraint bag is attached to thebottom of the EMU mount and covers the lowertorso of the EMU to restrain it during launchand entry. Straps on either side of the bag areattached to points on the upper part of the EMUmount and are tightened to ensure that theEMU is fully restrained.

For Spacelab/Spacehab module missions, theinternal airlock is used along with a tunneladapter that mates with the airlock and aSpacelab/Spacehab tunnel that is installed inthe payload bay. The airlock tunnel adapter,hatches, tunnel extension, and tunnel permit theflightcrew to transfer from the orbiter's pressur-ized middeck compartment to the Spacelab/Spacehab pressurized shirt-sleeve environment.An upper hatch in the tunnel adapter providesegress/ingress for EVA operations. The exter-nal airlock is used in conjunction with the tunneladapter during Spacelab/Spacehab missionswhen the orbiter is docked to Mir or the ISS. Inthe event of an EVA, the flightcrew is not pres-ent in the Spacelab/Spacehab.

EVA Support Equipment

A variety of equipment is available to supportthe EVA crewmember. Depending on the taskto be performed, the proper tool is availableoutside the airlock. The general equipmentfunctions include securing the crewmember tothe orbiter/RMS, providing the crewmemberwith mechanical assistance, and assisting thecrewmember in mobility. The following listitemizes the EVA support components with abrief description of their functions.

Crewmember safety tether - ensures the crewmem-ber is positively tethered to the orbiter whileproviding access to all areas of the payload bay.

Before airlock egress, this 55-foot safety tether isattached to a waist tether and remains attachedat all times during EVA, while the crewmembertranslates from one area of the payload bay toanother.

Slidewires - facilitate the translation of acrewmember and equipment in the forward andaft directions of the payload bay. Two slide-wires are installed for all STS flights on eitherside of the payload bay for a length of approxi-mately 46 feet.

Tethers - include waist and wrist tethers. Waisttethers are used to attach the crewmember tothe orbiter safety tether system and to provideadditional crewmember restraint at a worksitewhen required. Waist tethers use a large hookto be attached to various tether points(including the crewmember safety tether) and asmall hook that attaches to an EMU waisttether ring. Wrist tethers are used to securetools and hardware to the EVA crewmemberand to tether points. Wrist tethers are bothfixed and adjustable, attaching to loops on theEMU glove.

Handrails - aluminum tubing strategicallylocated to aid in crewmember translation orrestraint to accomplish a specific task. Hand-rails are located on the forward and aft bulk-heads, the hingeline of the payload bay doors,and the RMS end effector. Handrails aredesigned with tether attach points.

Portable foot restraint - a working platformdesigned to restrain the EVA crewmemberwhile performing contingency operations onvarious components of the payload bay systems.The portable foot restraint stabilizes thecrewmember by using a system of toe guidesand heel clips designed to interface with theEMU boots.

EVA Winch - allows the EVA crewmember toclose the payload bay doors in the event of apayload bay door drive system failure. Prior tolaunch, the winch is mounted on both theforward and aft payload bay bulkheads. Thewinch consists of a reel, assisted by springenergy, housing 24 feet of 3/8-inch-diameterKevlar rope with a hook attached to thefree end.

Provisions stowage assembly (PSA) - an aluminumtool stowage container mounted under thecargo bay liner, flush with the bottom of thepayload bay. Tool box tether protocol: whenstowing the tools in the PSA, the tools/toolcaddies are tethered before they are removedfrom the mini-workstation and untethered onlyafter they are securely placed in their corre-sponding storage cavity. The tools listed beloware contained within the PSA.

Mini-workstation - a mechanical device thatmounts on the front of the EMU to stow toolsand to provide a means of tether restraint for anEVA crewmember at a worksite.

Tube cutter - used for a contingency door-closingoperation. The tool consists of spring-loadedretention rollers, a cutter wheel mounted on aslide, a blade ratchet handle, a rotating body, acontrol lever, and a tube-cutter ratchet handle.It is designed to cut drive door linkages.

Payload bay doors disconnect tools - used todisengage the payload bay doors power driveunit(s) (two) from the power-drive-unit torqueshaft, allowing manual closing of the doors. Thetool is approximately 6-3/4 inches long from thetip of the tether ring to the end of the 3/8-inchsteel square drive extension. Additional toolsfor disconnecting the door drive linkage systeminclude vise-grip, ratcheting box-end wrench,adjustable wrench, loop pin extractor, Velcro/tape caddy, bolt puller, and trash bag.

Three-point latch tool - used to compensate for failedbulkhead latches. The tool consists of a stowableratchet handle, two interchangeable tool handles, aratchet control selection lever, a spring-loadedcompensator, and two fixed-load pickup points.

Centerline latch tool - used to compensate for a failedpayload bay door centerline latch. The toolconsists of a fixed-load and a spring-loaded pickuppoint, plus a reversible ratchet with a stowablehandle and a pair of trigger release buttons with asafety that prevents an accidental release.

Airlock latch disconnect tool - a common, EVA-modified, crescent wrench used to force open ajammed latch and/or latches disconnected fromthe rotary actuator. The other contingency air-lock disconnect tool is a drive ratchet with a7/16-inch hex socket and 4-inch extension.

RMS rope reel - used in conjunction with thesnatch blocks in the event of an RMS jointfailure. The reel consists of a rope spool, spoolbracket, rope guide, and cam cleats. The ropereel contains approximately 80 feet of 5/16-inch-diameter Kexlon rope.

Snatch block - a common marine device used, inthe event of an RMS failure, in conjunction withthe RMS rope reel and EVA winch to backdrivethe RMS to a stowed position.

Payload retention device (PRD) - used as an on-orbit temporary tiedown tool so that the articleor payload being secured can be repositioned asnecessary to prevent damage. It consists of ahousing that encloses a 15-foot Kevlar webbingstrap on a spring-loaded reel.

RMS manipulator positioning mechanism wrench(RMS MPM wrench) - a double-ended, open-endsteel wrench used to deploy or stow the MPMs(in the event the MPM motors fail) by manuallyturning the drive shaft in the appropriatedirection, thus allowing for payload deploymentand/or payload bay door closing.

RMS shoulder brace release - a flat steel bar withan angled foot used to disengage the RMSshoulder brace locking mechanism, thus releas-ing the shoulder brace. If the lock is notreleased, the RMS is inoperative.

Grapple fixture release tools - used to remove a grapplefixture shaft should an end effector malfunction,failing to release a payload. The tools include aprobe and 1/2-inch ratcheting box-end wrench.

Radiator actuator disconnect tools - A 3/8-inchdrive ratchet and 1/4-inch allen wrench exten-sion used to disconnect a failed radiatoractuator and support stowage of the radiators.

External tank umbilical door tool - used to overridea failed external tank door centerline latch andsupport ET door closure.

Generic jam removal tools - diagonal cutter, cablecutter, needle nose pliers, probe, hammer, pry-bar, forceps, trash bag. For use in disconnectingor dislodging jams in various orbiter mecha-nisms, such as PLBD hinges, latches, etc.

Portable foot restraint (PFR) bridge clamp - providesa PFR socket that mounts on the sill of the PLB inavailable locations on existing bridge rails.

Simplified Aid for EVA Rescue

The simplified aid for EVA rescue (SAFER) is asmall, self-contained, propulsive backpacksystem used to provide a free-flying rescuecapability for an EVA crewmember. SAFER is a"simplified," single-string system that fits on thebottom of the EMU PLSS and attaches to existingmounts on the sides of the PLSS. In essence,SAFER is a small simplified version of themanned maneuvering unit (MMU). Because it isintended for self rescue use only, SAFER does nothave the propellant capacity and systemsredundancy that was provided with the MMU.

SAFER is designed to be used as a self-rescue devicefor a separated EVA crewmember in situationswhere the orbiter is unavailable to provide rescuecapability. Such situations would include when theorbiter is docked to a large payload or structure,such as the Russian Mir Space Station or ISS. TheSAFER will also be used during all future ISS EVAoperations where the orbiter might not be present atthe ISS during an EVA.

To provide self-rescue capability, the SAFERoffers 13 minutes of propellant and controlauthority to stabilize and return a tumbling/separating EVA crewmember. The SAFER has24 gaseous-nitrogen (GN2) thrusters to provide6 degrees-of-freedom maneuvering control. TheSAFER is controlled by a single hand controllerhoused in a hand controller module box locatedon the bottom of the unit. The SAFER propul-sion subsystem provides a total delta velocity ofat least 10 ft/sec with an initial charge. Theflight unit weighs approximately 85 pounds andfolds for launch, landing, and on-orbit stowage.

The SAFER is the product of a Johnson SpaceCenter (JSC) in-house project to develop, build,and produce a rescue device for the instanceswhen the orbiter cannot provide rescue capabilityand for ISS EVA operations. An on-orbit SAFERdetailed test objective (DTO) conducted on spaceshuttle mission STS-64 was very successful. ThisDTO demonstrated SAFER's operationalcapabilities and collected performance data toaugment the design and development of the finaloperational SAFER. The STS-76 SAFER was atransitional unit between the DTO unit flown onSTS-64 and the final production unit that will bemanifested for ISS. The operational unit will becapable of being stationed on-orbit for 1 year;however, after use on orbit, the unit will bereturned to Earth for refurbishing.

Simplified Aid for EVARescue (SAFER)

Attachment of SAFER Unit to EMU

Operations

As previously discussed, there are three types ofEVA: scheduled, unscheduled, and contin-gency. A scheduled EVA is defined as any EVAincorporated into the normal flight plan in orderto complete a specific mission objective. Anunscheduled EVA is not part of the flight plan;rather, it is conducted to achieve payload opera-tion success or to advance overall missionaccomplishments. A contingency EVA is alsounscheduled, but is required to ensure safereturn of the orbiter and flight crew.

Regardless of the EVA type, a series of proce-dures are required to initiate and terminate anEVA. These procedures cover an integratedtimeline sequence from the EVA checklist. Thedetailed procedures are summarized for refer-ence in the following steps:

1. Quick don mask prebreathe - Donningof the mask for prebreathe and cabindepressurization.

2. Cabin depressurization to 10.2 psi -Reducing the cabin pressure from 14.7psi to 10.2 psi.

3. EMU checkout - Preliminary checkoutof the EMU systems prior to EMUdonning.

4. Middeck preparation and preparationfor donning - Configuration of theEMU and its ancillary components forcrewmember donning.

5. Suit donning - Crewmember donningof the EMU and ancillary components,approximately 40 minutes duration.

6. EMU check - Configuration and check-out of the EMU prior to EMU purge.

7. EMU purge - Nitrogen purge of theEMU prior to prebreathe.

8. Prebreathe - Crewmember acclimationto lower chamber pressure, over aperiod of 40 to 70 minutes.

9. Preparation for depressurization -Configuration of the airlock and

closing the inner hatch prior to airlockdepressurization.

10. Airlock depressurization - Configura-tion and checkout of the EMU, airlockdepressurization to vacuum, andopening of the outer hatch.

11. Airlock repressurization - Airlockrepressurization and opening of theinner hatch.

12. Post-EVA - Shutdown of the EMUsystems and doffing of the EMU andancillary components.

13. EMU maintenance/recharge - Change-out or recharge of the EMU batteryand lithium hydroxide cartridge andgeneral cleaning of the EMU forsubsequent EVA; recharge of the EMUwater system.

14. Post-EVA entry preparation - Recon-figuration and restowage of the EMUand airlock equipment.

A set of procedures are followed when acrewmember has contracted the bends duringan EVA. The crewmember discontinues theEVA and returns to the airlock to connect to theservice and cooling umbilical. The airlock isrepressed to 10.2 psia, and the cabin is repressedto 14.7 psia. The helmet is doffed, and thecrewmember drinks a minimum of 32 ounces offluids. After proper EMU reconfiguration, thebends treatment adapter is installed for bendsrecovery.

Scheduling an EVA is a very complex andinvolved task. The following list outlines thegeneral mission constraints regarding EVA, butdoes not attempt to define the detailed specificactivities.

The maximum scheduled duration foran EVA is 6 hours.

All scheduled and unscheduled EVAsrequire two crewmembers.

No scheduled or unscheduled EVA shalloccur on flight day 1 (~24 hours MET).

No scheduled EVA shall be planned tooccur prior to flight day 4 (~72 hoursMET) unless:

i) A specific flight is dedicated toscheduled EVA activity, and

ii) That payload customer hasspecifically negotiated with NASAfor the early scheduled EVAcapability, and an exemption isprocessed.

The latest an EVA may be scheduled inpreflight planning is EOM-2.

No unscheduled EVA shall be plannedto occur prior to flight day 3 (~48 hoursMET) unless:

i) A specific payload has no alterna-tive but to utilize an EVA as itsthird level of redundancy for thepurpose of a critical backup todeploy/operations that wouldprevent loss of the payload, and

ii) That payload customer has beenmade aware of the inherent riskthat the EVA may not be able tobe performed due to crew status,and the customer has agreed toaccept the risk, and

iii) That payload customer has spe-cifically negotiated with NASAfor the early unscheduled EVAcapability, and an exemption isprocessed.

The following are required response timesprior to an unscheduled payload EVA:

i) Upon the discovery of a failureleading to an EVA, approximately

24 hours are allotted for EVApreparation prior to startingactual EVA maintenance on afailed component.

ii) If the case above occurs on launchday, then approximately 44 hoursare allotted prior to starting EVAmaintenance.

iii) If a payload requires a shorterEVA response time, then therequirement for that EVA must benegotiated with NASA, and anexemption must be processed.

Payload activities that could require anunscheduled EVA at the end of amission may only be scheduled if thereare sufficient consumables and landingopportunities to extend the mission toperform the EVA and preserve 2 wave-off days.

A minimum of 1 flight day must sepa-rate two scheduled EVAs, for any givenEVA crewmember.

A contingency EVA will be scheduled inreal time whenever it is necessary torestore the orbiter to a configuration forsafe return.

Contingency EVAs occur if orbiter hardwaresustains a malfunction. Procedures, tools, andspecified work locations are identified forpractice on any STS mission. The recognizedfailures pertain to the following orbiter systems:radiator actuator, payload bay doors, bulkheadlatches, centerline latches, airlock hatch, remotemanipulator system (RMS), bulkhead camera,Ku-band antenna, and external tank doors. Thecorrective actions for each system failure areitemized in the following table.

FAILURE CORRECTIVE ACTION

Radiator actuator Radiator actuator disconnectPayload bay door system PDU

Winch operationsPLBD drive system linkage cutPLBD drive system disconnectElectrical crossover disconnectJam removal

Bulkhead latch 3-point latch tool installationJam removal

Centerline latch Centerline latch tool installationJam removal

Airlock hatch Airlock latch disconnectHinge disconnect

RMS RMS joint alignmentRMS tiedownMPM stow/deployRMS shoulder brace releaseGrapple fixture release

Bulkhead camera Disconnect and remove cameraKu-band antenna fails to align for stowing Ku-band antenna gimbal alignmentExternal tank door ET door centerline latch release

System Failure Corrective Actions Table

EVA Summary Data

EVA refers to operations performed outsidethe spacecraft crew compartment.

For generic orbiter missions, two suits areincluded with consumables provided forthree, two-person, 6-hour EVAs.

There are three basic categories of EVA:scheduled, unscheduled, and contingency.

The extravehicular mobility unit (EMU) is anindependent anthropomorphic system thatprovides environmental protection, mobility,life support, and communications for thecrewmember to perform EVA in Earth orbit.An EVA is defined, for EMU design consid-erations, as any time the EMU externalenvironmental pressure is below 4.0.

The EMU is an integrated assembly, primar-ily composed of the space suit assembly, lifesupport system, and numerous items ofassociated support and ancillary equipment.

The orbiter's airlock permits EVA flight crewmembers to transfer from the middeck crewcompartment into the payload bay in EMUswithout depressurizing the orbiter crewcabin. The airlock also provides launch andentry stowage of up to three EMUs.

The airlock's support functions include air-lock depressurization and repressurization,EVA equipment recharge, LCVG water cool-ing, EVA equipment checkout, donning, andcommunications.

Depending on the task to be performed, theproper tool is available outside the airlock.The general EVA-support equipment func-tions include securing the crewmember to theorbiter/RMS, providing the crewmemberwith mechanical assistance, and assisting thecrewmember in mobility.

A standard series of procedures (pre and postoperations) are required to initiate and termi-nate an EVA, regardless of the EVA type.

EVA Rules of Thumb

Always use "make before break" tether proto-col.

Don't use the glove as a hammer.

EVA crewmember and equipment mustremain tethered at all times.

Slow and deliberate motion provides muchgreater stability than quick, jerky motions.

Body positioning is 90 percent of the task.

Each EVA crewmember should check out hisor her own EMU.