ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
TQ471 TQ471 ft---_-I_.... f .1',cablelength max.2m  ,os13,I..;_coNDITIONER ,. _\._".L coaxial cable <5mm Figure1.HighResolution Standard Proximity Sensor DMS134 Technology Thechoiceoftheeddycurrent technology wasconsidered asthebestall-around performer andmost suitable andadaptable totheinstallation requirements. Thechoiceofthistechnology wasalsotheresult ofaquestionnaire senttothespaceindustry worldwide. Aneddycurrent measuring system operates inanRLCparallel network wheretheamplitude ofthe oscillation isproportional tothedisplacement tobemeasured. Thepassive sensorconsists ofacoil(L) andacable(R,C)fedbyahigh-frequency excitation generated byanearbyconditioner. Thetaskofthe signalconditioner istogenerate thehigh-frequency oscillation andtoconvert theresulting signalintoa linearoutputproportional totherelative distance ofthetarget.Thesensitivity ofthesystem isdependent onthematerial, mounting constraints, andtherelative displacement ofthetargetfromthesensor. Technical description oftheHRSPS Twosensors (typeTQ471)andtwoelectronics conditioning channels located insidetheIQS134 conditioner arerequired foradifferential arrangement measurement (Figure 1).TheTQ471sensor includes acoil(position measurement element), atemperature sensing element andacableofupto2 meters. Sensor temperature monitoring permits zeroandsensitivity driftcompensation independently foreach measuring channel. Theelectronic conditioner IQS134alsoincludes itsowntemperature monitoring, allowing independent compensation oftemperature gradients upto220Kbetween thesensorheadsand theconditioner. Bothsingleanddifferential outputs arepermanently wiredontheconnector. Transfer Functions andMeasuring ranges withdifferent sensor configurations Theinitialrequirement wasforamaximum rangeoflessthan25mm(1in).Inordertoachieve thelow linearity errorrequired fornanomeasurement inspacemechanisms, thestandard measuring ranges weresetasbelow.Theoutputvoltage vs.displacement isshowninFigure6. Transfer/differential TQ471 10 TQ472 5 TQ473 1.66V/mm Single 1mmMeasuring range Differential +0.5mm 2mm +1mm 6mm +3mm NASA/CP--2002-211506 148
Thestandardmeasuringrangesabovedonotlimitthecapabilityoftheeddycurrentmeasuringsystems. Forinstance,Vibro-Meter offersHRSPSmeasuringsystemswith+50%measuring rangeastheones indicatedabovewithsensorheaddiametersof5mmfortheTQ471,8mmfortheTQ472and18mmfor theTQ473.SeelinearitytestsresultswithTQ471with9mmrangeonFigure6.ThefinalHRSPSwillbe acompromise betweenthedifferentparameters definingthefinalperformance ofthe:system. Advantages overotherTechnologies Truecontact lesstechnology Repeatability Smallsensorheadsinanaction-free environment -Singleanddifferential arrangement -Sensor andtargetextreme temperature capabilities (+125to-150°C) -Sensor headandconditioner individual temperature compensation -Highvibration survivability (random 30grms) -Highradiation survivability (Sensor 108Rad) -Operational inharshenvironment -Modular channel configuration (expandable upto4sensorheads) Accuracy Theaccuracy isdefined asthecombined errorduetorepeatability, non-linearity, hysteresis andthe resolution limits(electrical noise).TheHRSPS hastheoretically norepeatability errorbutthetemperature deviation of100ppm/°C willdeteriorate thepractical repeatability ofameasurement. Wetherefore assume arepeatability errorof1%.Thelinearity achieved is0.5%inthedifferential arrangement and1% inthesinglearrangement (Figure 6).TheHRSPS couldbesupplied witharawoutputinformofa polynome. TheHRSPS system hasnohysteresis andtheresolution errorissolowthatitbecomes negligible inthecalculation oftheaccuracy. Basedontheabove, theaccuracy is1.1%indifferential arrangement and1.4%insinglearrangement. LifeandReliability Thetransducers andtheconditioner aredesigned foratotallifeof15years.Thecalculated reliabilities for aflightmodelequipped withtwosensors andoneconditioner are: Microgravity andforISSusing883Bcomponents: MTBF>1,700,000 hours HighReliability Satellite: MTBF>2,500,000 hours Mechanical Design Thesensor casingismadeoutofamachinable ceramic, whichoffersreduced thermal expansion. The sensors arequalified withamechanical interface represented asascrew(TQ471:M6 x0.75,TQ472: M10x1andTQ473:M20 x1.5)withaxialcableoutput(Figure 2).Thissimplemounting haseasedthe largeamount oftestingontheexisting Vibro-Meter in-house ground support equipment. Different sensor casings withradialoutputs willalsobequalified. Electrical Characteristics TheHRSPS offersthechoiceofworking with+15VDCor+28VDCpowersupply. TheHRSPS outputis 0to+5VDCinasinglearrangement and+5VDCinadifferential arrangement forthefullmeasuring range.Onrequest, theoutputs canbeincreased to7VDC.Outputs (differential &single) arealways available ontheoutputconnector. Thereisroomfortheinstallation ofafuseinthe+28VDCpower supplylineonrequest. Theimproved naturalfiltering easesafurtherdigitalization (sampling). Thedesign oftheanti-aliasing filter,whichmaybeincascade withtheHRSPS incaseofdigitalprocessing, willonly havetoconsider themechanical targetfrequencies (Figure 5). NASA/CP--2002-211506 149
Modular Construction Theelectronic conditioner IQS134ismadeof2frames (Figure 3): OnePowerSupplyframeforeither+28VDCor+15VDCvoltage -OneConditioner frameconnected totwosensorheads. Thepowersupplyhasbeendesigned topowertwoconditioner frames. Whenmorethantwosensor headsarerequired, itispossible toaddasecond conditioner frameabovethefirstone.Inthiscase,the4 sensorheadshavetobethesameasthereisonlyoneoscillator forbothframes inordertoreducethe coupling. Thisconfiguration allowstouseupto4singlesensors or2singleandonedifferential or2 differentials. Thismodular concept offersthefollowing advantages: Totalmassreduction Powerconsumption reduction Costreduction Mixedconfiguration without calibration change (single anddifferential outputalways available on connector). Environmental Requirements Thefinalqualified HRSPS responds toESAECCSStandards aswellastoMIL-STD-1686, MIL-STD6001andSSP30237130242150005157000 fortheISS.Itisqualified formostofthelauncher environments thatareflyingtoday. Conclusions TheHRSPS isatruecontact lesseddycurrent measuring system qualified forspaceapplications. Ithas ahighdegree ofadaptation totheinstallation andtheenvironment requirements. Itoffersanexcellent repeatability andaccuracy forapplication onspacemechanisms requiring rugged conditions (30grms).It offersagreatflexibility allowing trade-offs withtheresolution /linearity versusthemeasuring range.The repeatability andthelinearity errorspractically depend onthetemperature deviation, whichremains the limiting criteriaofthetechnology. Practical applications havemeasuring ranges upto9mm(0.35in)with aslightlyreduced resolution (Figure 4).TheHRSPS isflexible enough toofferothercompromises. TheHRSPS mainperformance parameters are: Resolution of1nmforameasuring rangeof+0.5mm,1.4nminsinglearrangement for1-mmrange (100Hzbandwidth at1kHz). Resolution of2nmforameasuring rangeof+1mm,2.8nminsinglearrangement for2-mmrange. Resolution of7nmforameasuring rangeof+3mm,10nminsinglearrangement for6-mmrange, Resolution of16.5nanometer fora9-mmrangeinsinglearrangement (Figure 4). Frequency response 16.5kHz(-3dB)atmax.gap(Figure 5). Sensor operation to-150°C (-238°F) allowstheintegration oftheHRSPS formissions toMars. The -HRSPS mainachievements are: Linearity of0.5%indifferential arrangement and1%insinglearrangement (Figure 6). Accuracy betterthan1.1%indifferential arrangement and1.4%insinglearrangement. FlightModel(DMS134)usingtheHighReliability version forscientific /commercial satellites. FlightModel(DMS124)in883Bqualityformicrogravity andfortheInternational SpaceStation. Modular designwithamixofupto4sensorheadsandoneIQS134. Single modeoperation allows costreduction andeasestheconfiguration (mixofsingleand differential). TheHRSPS istheonlytruecontactless displacement measuring system operating withina temperature rangefrom-150octo+125°C (-238to257°F). NASA/CP--2002-211506 150
TQ473,IQS134insinglearrangement at9mm.gap Equivalent RMSI/Pnoise(FSD/VHz) 9.00E-07 8.00E-07 7.00E-07 6.00E-07 5.00E-07 4.00E-07 3.00E-07 2.00E-07 1.00E-07 0.00E+00i  i , II F 10i 100 Fr_quence/I-IZ1000 10000 Figure4 100 0 -1 -2 -3 A tn-4 ,,o _"-5 -6Frequency Response TQ473,IQS134, singlearrangement atmax.gap9mm. -7 -8 -9 -101000 10000 100000 IIILIs '1,,.r]iiiii'_--1-3dB ati6.5KHz Frequency (Hz) Figure5 NASA/CPp2002-211506 153
Uout=f(gap) TQ471,IQS134insingle arrangement 4.5 4.0 0 Z0 15 I1) ([5 00 ooj" ////._ ............. 04 0.6 0.8 Distance Sensor -Target VCL140(gap/mm) .............. 1.0%Linearity TQ471,IQS134insingle arrangement 0.8% 0.6% 0.4% v ,.-0.2% w0.0% -02% ¢-._ -_-04% -0.6% -0.8% -1.0%............ q.... 0.0 0.2 04 06 Distance Sensor -TargetVCL140(gap/mm) Figure60.8 1.0 NASA/C P--2002-211506 154
Qualification oftheInflatable Sunshield InSpace(ISIS)Mast DavidJ.Rohweller* Abstract TheInflatable Sunshield InSpace(ISIS)mast,Figure1,isanewtelescopic mastthatwassuccessfully qualified forflightontheSpaceShuttle. Thispapershares someofthesuccesses andfailures we experienced andlessons learned aswewentthrough thisprocess. These included successful accommodation ofcustomer drivenchanges, theeffectofthermal analysis ondesignandcostrisk,better waystodesignformanufacture andassembly, solvingtestfailures, andtheeffectofsizeonoverallcost. Introduction TRWAstroAerospace builttheISISmastfortheNASAGoddard SpaceFlightCenter (GSFC). Itis designed tocarrya136-kg (300-1b) payload forlaunchonaShuttle Hitchhiker palletandthendeployit 6.7m(22ft)awayfromthepayload bay.Theintentwastoprevent theexperiment, aninflatable sunshield, fromcontacting anypartoftheOrbiteroranypayloads inthebayasthe,experiment deployed. Aftercompletion ofthedeployment andrelated experiments, themastandshieldareejected fromthe Shuttlebay. Thestowed ISISmastisshowninFigure2withthevarious itemsofequipment mounted onitidentified. Themastoutercanister mounts onaSpaceShuttle Hitchhiker palletwithaMarman clampbandprovided bythecustomer. Thiscanister istheprimary structure thatcarriesthepayload duringlaunch. Thepayload isattached tothetopoftheoutercanister viaatipplateandanother clampbandthat secures thetipplatetotheupperendofthecanister. Thetipplatealsopreloads andcagestheinner segments ofthemastforlaunch. Todeploythemast,theupperclampband(notshown) isopened viaa pyrotechnic cutter,whichreleases thepayload andtheinnercanister segments fordeployment. Afterrelease, themotoristurnedonandaStorable Tubular Extendible MastTM(STEM) pushes themast out.Ineffect,themastispulledoutfromthetipbypushing fromthebottom. Thedeployment is sequenced sothatthemastdeploys fromtherootwitheachcanister locking intoposition beforethemast continues itsdeployment. Thisinterlock system isshowninFigure3. Thetwo,1.9-cm(3/4-inch) diameter electrical payload cablesaremounted inacageinsidetheinnermost canister ascanbeseeninFigure4,whichshowsthetopandinsideofthemast.Asthemastdeploys the cageuncovers thecableanditfeedsitselfoutandtightens itselfaround theSTEMTMinaspiral.Thismast issimilartoabreadboard designpresented atthe28thAerospace Mechanisms Symposium, exceptitis fivetimeslargerindiameter andrepresents thefirstflightqualification ofthismast.Table1givessomeof thedataforthismastasareference. Themastsuccessfully completed alltherequired objectives andwasshipped toGSFC.Unfortunately, the ISISprogram wascancelled andthemastiscurrently residing ingovernment storage. TRWAstroAerospace, Carpinteria, CA Proceedings ofthe3_hAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/CP--2002-211506 155
Table1.ISISMastData Description Diameter Average Diameter Stowed Length Deployed Length Number ofSegments TimetoDeploy Bendinq Stiffness AxialStiffness Bendinq Strength Torsional Strength Deployed Natural Frequency with136kgPayloadValue 61cm(24in) 51.44cm(20.25in) 67.95cm(26.75in) 6.7m(22ft) 12 3min 1.93x106Nm2(4.2x106Ib-ft2) 50.7x106kN(11.4x106Ibf) 1,853Nm(1,365Ibf-ft) 2,813Nm(2,080Ibf-ft) 1.7Hz Project Events Design Changes Design changes afterthestartofaprogram arecommon andthisprogram wasnodifferent. Changes to theISISexperiment required themasttoincrease insize.Thedesignitselfismodular andiscapable of accommodating changes suchasthiseasily.However, someoftheminordetailspresented challenges thatwereunforeseen. Thebiggest change wasthatthepayload increased from91to136kg(200to300Ib).Thisforcedthe outermost canister, whichcarriesthisloadasacantilever, toincrease from45.7to61.0cm(18to24in) indiameter tosupport theloadwiththerequired stowed naturalfrequency of50Hz.Inaddition tothis,the lengthofthemastincreased from6.1to6.7m(20to22ft).Thepracticalities ofroutingalargecableinto themastcaused thestowed lengthtoincrease, whichincreased thestowed bending moment dueto launch loads.Overall, thestowed stiffness increased byafactorofalmost fourovertheoriginally proposed design. These rathersignificant changes wereaccommodated withminimal impact tothe program duetothescaleable natureofthemast.Thechallenges weexperienced werecaused bytight tolerances andadditional hardware interface requirements asaresultofminordesignchanges. Toaccommodate theratherlargeloadsattheinterface, aMarman clampbandprofilewasspecified that required atolerance of+0.0and-0.1degree. Thistolerance required theangleoftheprofiletobeheld within+0.3p.m(+0.00014 inch)overitslength. Thisproveddifficulttomachine andinspect. Another change wastheaddition ofhandholds andfittings tothestructure. Thesewerecustomerfurnished equipment (CFE)necessary forsafetyandmission success. Engineering addedthesetothe canister incollaboration withthecustomer fairlyquickly. However, theadditional hardware significantly increased thenumber ofcustomer interfaces thatquality assurance hadtoverifyandincreased the chances forassembly problems. Whenitcametimetointegrate theCFEwefoundasubtledifference in howthesepartsweremade.TheCFEhadthreaded holesthatmatedwithholesonourcanister. Their holesweredrilledtomaketheirpartseasytomake,thatis,invertical directions ratherthanradially. Our canister ontheotherhand,whiledimensioned thesameway,wasmadeintheeasiest waytomakeit, withtheholesandcountersinks drilledradially. Whenthetimecametomountthehardware, theholes NASA/CP--2002-211506 156
Tapered Hole /,//_" Tapered ...... PinDeploying ,,-OuterTube / / J_MiddleTube / / / /' --NextInnerTube ,f _"il,'i/il ._,.._i-'-__2_</_z_ _'_"Deployment _._i_ _+._,_¢!D;_ _Direction ",Tube _1',Lower i_,Ringt_ -OutertubeSequenced !_._,-:i i "Conical Detent (Shuttle Latch)10550 Figure3.Canister Sequencing Interlock NASA/CP--2002-211506 162
10555a TestResults Area: 2.0625 in-" PeakLoad: 1001.0000 Ibf PeakPosition: 0.0557 in ChordModulus: 17006.4000 lbf/in .O O .-1 Position (in)J '75 Counter: Elapsed Time: SWO#: Specimen 1D: Material: Comments: Sample: Procedure Name: StartDate: StartTime: EndDate: EndTime: Workstation: TestedBy:TestSummary 8766 00:01:12 1896ISIS TwoLayers Smcone Rubber 0.067"X 0.75 11Bars.25wide/.02 space Contact Size2.75X0.75 VibePlateRubber Damper 07/11/2001 11:33:21 AM 07/11/2001 11:34:33 AM GP5-200-SATEC CS788 RobertHombeck Figure8.Silicone Rubber SpringRate NASA/CP_2002-211506 167
•Onceproperunlatchingisverifiedbytheinternaltelemetryandvisual"inspection" frombothEVAand theavailablevideocamerasontheOrbiter,theextensionofthedeployable mastisperformedbythe motordrivenMastCanister.Asthemastdeploys,thetwosolararrayblankets,eachconsistingof82 solararraypanels,areunfoldedfromtheirstowedposition.Themastextensionnominallyrequires approximately 12minutes.Threelightlytensionedguidewires perblanketprovidemanagement ofthe unfoldingpanelsbyguidingeveryotherpanelhingelinewhiletheouter-most andinnermostpanelsare attachedtotheirrespectiveContainment Boxstructures. Springmechanisms evenlydistributethe tensionforcesonthepanels.Internaltelemetryofthisoperationincludesonlymotorcurrenttime history,fullyretracted&fullyextendedmastlimitswitchsignalsandincidentalblanketshuntcurrent readings. •OncetheMastisfullyextended, thefinaldeployment operationrequirescommanding the Latch/Unlatch Mechanism backtoits"latched"positioninordertopositiontheTensionMechanisms intotheir"high"tensionmodetofullypreloadthedeployedsolararrayblankets.Thisoperationisdone oneblanketatatimeduetoavailablepowerlimitationsandisrequiredtoprovideproperfrequency andstrengthtothefullydeployedsolararrayblankets.Internaltelemetryconsistsofmotorcurrenttime historyandlatch/unlatch limitswitchsignals. Figure3showsafullydeployedsolararraywing. Rear View IK_Top\\ Rotation direction ofleftcontainment boxView I \_ toon-orbit ready-to-deploy position i. •_ _-i i :i i" : _t> I // Rotation direction ofrightcontainment box d-/'toon-orbit ready-to-deploy position RightSide View _.h"-,Ti_'_---_-:-' '_ "" -- '''""i,;...... r; ., ..;, -1.______I Bottom View \\ //h-_rm__ .' Figure1.ISSSolarArray-Stowed Configuration NASA/CP--2002-211506 171
z Direction toSun Canister tipfitting Solararray blanket(2) Containment boxbase(2) Foldable articulated squaretruss(fast) mast Canister motor driveassembly MastCanister Assembly_Upperpivotfitting "(2) ",,_/_=_ _Containment "__ 7b(;_.cover(2) fitting(2) __ Figure2.ISSSolarArray-Partially Deployed Configuration (MastExtending) Specific detailsofthevarious mechanisms associated withthesolararraydeployment arediscussed in References 1and2.However, tensioning oftheBlanket isparticularly relevant totheSTS-97 activities andwillbefurtherdescribed here.Thetwo-level blanket tensioning mechanism (i.e.,lowtension during mastdeployment andhightension forafullydeployed wing)developed relatively lateinthedesignofthe solararraysandwastheresultofbothevolving requirements andevolving analyses. Atthatpointintime, thebestunderstanding ofboththerequirements andtheavailable analyses indicated thattheextendable mastmightnotwithstand theapplication oftherequired deployed blanket preload duringthemast extension. Animportant consideration intheanalyses included thefullrangeofpossible tolerance stackupsofthevarious mechanical hardware. Thedesignsolution tominimize cost,schedule andweightat thatlatepointinthedesignwastochange thesinglelevel"high"tension mechanism toatwotension levelmechanism bylinkingtheTension Mechanism totheLatch/Unlatch Mechanism through pulleys, cables andsprings. Thiswouldprovide a"tow"tension ontheblankets duringmastdeployment to minimize thepossible dynamic loading ofthemast(particularly inthefinalseveral inchesofextension) whileallowing asecond operation oftheLatch/Unlatch Mechanism toapplythe"high"tension tothefully extended mastandsolararrayblankets ensuring propersolararraywingfrequency andstrength. The additional cablesandthelowering ofthecablepreload duringdeployment furthercomplicated existing concerns aboutcablemanagement. Thedesigncompromise thatresulted fromthetradebetween various competing design requirements (including EVAsafetyissues, relative mechanism motions, an88,000 NASA/CP--2002-211506 172
cycleTensionMechanism strokelifeandconcernsforaddingbindingfailuremodes)includedcable keepersonthesimplepulleysbutnoadditionalrestraintsontheTensionMechanisms' spiralpulley (Figure4). SolarArrayBlanket (82panelseach) Mast 1382in. max Tension Distribution Bar MastCanister Figure3.FullyDeployed SolarArrayWing EVADesiqn Requirements Inaddition tothetypicalspacecraft design requirements, thesolararrayprogram included avariety of EVArelated designrequirements. Theserequirements included various toolandastronaut capabilities for planned EVAoperations, requirements formanual back-up modesfortheautonomous operations, anda varietyofsafetyrelated requirements. Although EVAdesignrequirements areinteresting andcomplicated enough forseveral papersoftheirown,onlythesafetyrelated requirements arerelevant tothispaper.Of particular interest duringthedesignweresafetyconcerns regarding pinchhazards, sharpedges,relative motions, etc.thathadasonegeneral design solution theinclusion ofsomeformofrelatively smooth coverovertheareasofconcern. Giventhecomplicated natureofthemechanism functions andthelimits onenvelope, weightandassembly access, thedesignofthemechanisms couldnotbehazard freeand covers atmanylocations werediscussed atlengthduringthedesign process. Thecompromise that resulted fromthedesigntradeswastheinclusion ofrelatively fewcoversneartheplanned EVAoperation areasandknownback-up modeEVAcontingency areasandthedesignation oftherestofthewingas "EVAExclusion Zones" (Figures 4and5).Thiswasdonewithnaiveconfidence thatnoEVAwouldbe required nearmostoftheContainment Boxmechanisms, andithadtheunintended benefits thatit NASA/CP--2002-211506 173
allowedverydetailedon-orbitmechanisms inspections andunplannedcontingency repairoptionsthat otherwisewouldhavebeenimpossibleifcovershadbeenincorporated. Figure4.TensionMechanisms &CableManagementPulleywith partialguide SpiralReel Guidewire Mechanism Cover Pulley Cover I/BTension Mechanisms (withcover)Tension Mechanism O/BTension Mechanisms (nocover) Figure5.Tension Mechanisms &CableManagement -Close-up NASA/CP--2002-211506 174
STS-97 SolarArrayDeployments -"Howitactually worked..." Deployment Anomaly -FirstWinqDeployment Duringthedeployment ofthefirstwingonSTS-97, unexpected adhesion between thesolararraypanels caused somepanelstosticktoeachotherduringdeployment. Whenthepanelseventually brokefree undertheforceoftheTension Mechanisms, theresulting dynamic motions induced inthepanels and deployment mechanisms weredramatic, causing substantial shaking ofthedeploying blankets and associated structure. Thissticking thenbreaking freeoccurred multiple timesoneachblanket, andin someinstances theadhesion forcesandlowmechanical advantage ofthefoldedpanelswassuchthat theblanket tension distribution bar(whichisspringloaded bytheTension Mechanisms through cables andpulleys asshown inFigures 3and6)waspulledofftheContainment BoxBaseformanyinches beforethepanelswouldbreakfree.Oncethepanelsfreedthemselves, thebarwouldberetracted, or "reeled in,"bytheforcesoftheTension Mechanisms untilitimpacted theContainment BoxBase. Eventually, oneoftheseretractions andimpacts caused oneoftheblanket tensioning cablestojumpits spiralpulleyandallowaslackcable. Asubsequent sticking andretraction eventcaused thesecond tensioning cableonthatbartosimilarly de-spool. Although thisanomaly wasnotreadilydetectable by internal deployment telemetry ortomostobservers ofthedeployment video,itsramification forproper wingperformance wasverysignificant. Asdiscussed inprevious paragraphs, theblankets mustbefully tensioned toprovide proper solararraywingfrequency andstrength, andwithslacked tension mechanisms thepropertension couldnotbeapplied tooneoftheblankets. Tension Distribution Springs Tension Bar Figure6.Tension Distribution Bar;ionCable (1of2perblanket) Fortunately, theresolution ofthe"routinely" available videocoverage wasadequate toalloweasy detection oftheanomaly whenviewed byindividuals familiar withthedesign. Theswiftness and conclusiveness inconfirming thepresence oftheanomaly wasjustthefirstofmanyadvantages provided bythemanned deployment operations duringthecourseofthetroubleshooting andrepair. NASA/CP--2002-211506 175