ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Thespringsthatconnectthepistonstothehousingseachhavearateof158N/m(17.9Ib/in).Each housingintheADAMSmodelcontainsonlyonespringelementsotheeffectiverateis317N/m(35.8Ib/in). Eachspringelementhasapreloadintheinitialpositionthatstartsthedeployment motion. Interactionbetweenthelinkandhousingsismodeledwithcurve-to-curve contacts.Contactalongsmooth curvesproducesmoreaccurateresultsforslidingmotionsthandocontactsalongfacetedsurfaces.Spline curveswereaddedtoeachsideofthehousingandtothelink.Thesecurvesfollowthehousingandlink profilesmorecloselythanthesimpleextrusiongeometries usedtomodeltheparts.AsshowninFigure4, thecurvesactuallyextendbeyondtheedgesofthehousings.Theextensionswereusedtohelpthecurvecurvecontactdetectionalgorithmquicklyresolvethepointatwhichthetwocurvestouchatthestartofthe simulation. Figure4.ModelDuring Deployment Eachtwo-dimensional contact includes normalforce(impact), transverse force(friction), andtorque(also duetofriction). InFigure5,themodelhasreached thefinaldeployed position. Thesprings pullthepistons, whichinturnpulltheendsofthelinkintothehousing slots.Therearenormalforcesoneachsideofeach housing sotherearealsofrictional forcesateachlocation. Thesefrictional forcesprovide thelatching effect ofthemechanism. Engineering handbooks reportthecoefficients offrictionbetween aluminum andmildsteelas0.61staticand 0.47dynamic [Reference 2].Thesevaluesdonottakeintoaccount thecoatings usedonthehousings and linknordotheyincludetheeffectsofvacuum thatwillbepresent inflight.Theanalysis effortfocused onthe dynamics withvarying amounts offriction. Themodelwasrunwithdynamic coefficients offrictionof0.2,0.3,and0.4.TheplotsinFigure6showthe anglesbetween thepistonandlink.Angle1isforthehousing ontheleftthatwasattached tothegrounded panel.Angle2 isthepiston-link angleonthesidewiththepanelthatmovedduringthedeployment simulation. Whenthecoefficient offrictionis0.2,thepanelover-deploys almost90degrees andhasnotcaptured bythe endoftherun.Inthehighfrictioncase,thepanelover-deploys byapproximately 10degrees andisquickly captured intothefinalposition. Higherfrictioncoefficients wouldresultinevenlessover-deployment. Note thattheAngle2curvesaresimilarforallthreecases. Thelinkquicklysettledinthehousing onthe deploying panelsothatanyover-deployment wasduetomotioninthehousing onthegrounded panel. 227
Figure 5.ModelinDeployed Position 200.0 150.0I00.0150.0" 0,0 O.OL*"--",_u=o.2 i i mu=O.4 i IO0.O-1.O 2.0 3.0 4.0 5.0 time(seo) C'480.0" 60.040.020.0 0.0 0.0 1.Q Figure6.2.0 3.0 time,(see)° Angles Between LinkandPistons4.0 5.0i= Pistondisplacement isplottedinFigure7.Piston1 isinthehousing onthegrounded panelwhilePiston2 is onthedeploying panel.Withlowfriction, thePiston1 curveshowshowthelinkispulledoutofthehousing byover-deployment. Atacoefficient offrictionof0.4thepistonmovesintothecaptured position. The Piston2 curvesreflecttheAngle2curvesinthatthehousing onthedeploying panelquicklycaptures thelink anddoesnotexperience anypulloutmotion. 228
t.0 '_O.5 ,F, I , i i ! imu--O.4 ........................... _ "i r7_-- L-.... i i t.0 2.O 3JO 4,0 time(se¢)0.0 0.0 5.0 1.0 0.5 1.0 2.0 3.0 time(seo) Figure7.PistonDisplacementso.oo.o '4:0 5.o Oneconcern withthismechanism designisthepossibility ofhighloadsbeingapplied tothesolarpanels duringdeployment. Thisrigidbodymodelpredicts thedeployment motionbuttheresulting contact forces canbehighinmagnitude (seeFigure8).Intheactualsolararraythepanelcanflexwhenthelinkispulled intoahousing thatresultsinlowerforcesplusstructural damping. Furtherworkinthisareawillneedtouse flexible bodiesforthe_anelstoaccurately findloadsandstresses. 100.0 i i i 75.0" .._.., 50.0I "_.._ I 't25.0T 0.O 0.0 1.0 2.0 3.0 4.0 5.0 time(sec) Figure8.Contact ForceMagnitude Thegoalofthisanalysis effortwastoextendthemodeltosolararrayswithmultiple panelsandseveral hinges. Unfortunately, theapproach described inthispapertookasubstantial amount ofdevelopment and theexecution times(several minutes evenonafastcomputer) weretoolong.Analternative approach would betousethepresent modeltodevelop ananalytical representation ofthelink-housing interaction. For 229
example,atorquecouldbeappliedonthelinkthatincludesanimpactfunctionthatisdependentupon pistonposition.Suchamodelwouldrunsubstantially fasterwhileaccuratelyreflectingthedeployment dynamics. Ground Testing Asolararraythatincorporates hinge/latch mechanisms hasbeenfabricated andtestedfortheTSX-5 spacecraft [Reference 3].Fourdifferent typesoflinkswereusedinthedesign. Ground testingofthis designwasasignificant challenge duetothecomplexity ofthedeployment motion. Testswereperformed usingcablesandheliumballoons tooffsetgravity. Thetestsweresuccessful andprovided confidence inthe arraydesign. FlightExperience Aninitialversion ofthehinge/latch mechanism wasusedontheEarlyBird spacecraft thatCTASpace Systems (laterpartofOrbitalSciences Corporation) builtforEarthwatch. Thesolararraysdeployed successfully butanunrelated powersubsystem problem endedthemission afterfourdays[Reference 4]. Figure9showstheEarlyBird spacecraft withthesolararraydeployed. TheADAMS models described earlierwerebasedononeofthehingetypesusedontheTSX-5solararray.Themission wasscheduled for launchinlate1999buthasbeenpostponed toMarch2000[Reference 5].Asaresultflightdeployment resultswerenotavailable beforethepublication deadline. Figure9.EarlyBird Spacecraft Conclusion Thehinge/latch designrepresents auniqueapproach tosatisfying structural requirements forboththe stowed anddeployed configurations. Deployment dynamics ofarraysusingthesemechanisms are challenging toanalyze andtestbutflightexperience todatehasbeenpositive. Ananalytical representation ofthehinge/latch isbeingdeveloped inordertobuildmodelsofcomplex solararrays. Acknowledgements Theauthors wishtoacknowledge WalterHolemans whodeveloped thehinge/latch mechanism designwhile atCTASpaceSystems. Healsodirected thedetailed designofthecomponents thatwereusedonthe EarlyBird andTSX-5missions. References 1.Building Models inADAMSView, Mechanical Dynamics Inc.,1999. 2.Avallone, E.A.andBaumeister Ill,T.,Mark'sStandard Handbook forMechanical Engineers, Tenth Edition. McGraw-Hill, 1996,page3-23. 3.DetailsoftheTSX-5program areavailable athttp://www.te.plk.af.mil/TSX5HOME/TSX5.cfm 4.Foradescription ofEarlyBird spacecraft seehttp:llwww.digitalglobe.com/companylspacecraftlearlybird.html 5.TheVandenburg AFBlaunchschedule isavailable athttp://mocc.vandenberg.af.milllaunchsched.asp 230
Figure 1.ISIS1/=-Scale Model Background Thewirebrakewasdesigned toenablethecontrolled deployment ofaninflatable boom. Ingeneral, inflatable boomsmustactasstructures duringdeployment, andtheymustdeployinacontrolled manner. Onewayofcreating aninflatable boomistomakeacylindrical tubewithendcaps.Theunpressurized tubecanbeflattened androlledontoaspool.Byintroducing inflation gasintothefreeendofthetube, thetubewillunrollfromthespool.Thespoolrotates astheboomisdeployed. Acontrolled deployment mechanism isusedtoregulate therotation rateofthespool.Theresistance ofthespoolissetatalevel thatallowsadequate pressure tobemaintained intheinflated portionoftheboomwhilethedeployment envelope andrateremainpredictable. Figure2showsthecontrolled deployment mechanism usedfor ISIS............... =_z =. Figure2.ISISControlled Deployment DevicewithBoom 232
Inflatable Boom Yoke _ _ Reaction ArmWireBrake InsideSpool Spool Figure3.Controlled Deployment Device Thewirebrakeconsists ofaninputshaft,asupplydrum,atake-up drum,bearings, andaductilewire (Figure 4).Whenthespoolisrotated relative totheinputshaft,ductilewireiswrapped around thetakeupdrum,asitunwraps fromthesupplydrum.Duringthewiretransfer, mechanical energyintheformof rotarymotionisconverted toheatenergy. Thebending andunbending ofthewireasitunwraps fromthe supplydrumandwrapsontothetake-up drumaccounts fortheenergy conversion. Bearing Housing IllI_---- Reaction Arm  Bearing Housing  upplyDrum  uctileWire  Reaction Arm Figure4.WireBrakeMechanism Schematic _Theory ofOoeration Inordertoselectthewirematerial, wirediameter, anddrumdiameters, asimpletheorywasdevised to calculate theapproximate strainofthewire.Usingthestrain,theaverage stressofthewirecouldthenbe determined fromthestress-strain curve.Theaverage stressandcross-sectional areaofthewireare usedtocompute theforceinthewire,whichisusedtocompute thetorquerequired towrapthewireona drum.Thesuccess oftheanalysis, however, reliesontheaccuracy ofthestrainestimate. Theinitialgoaloftheanalysis istopredicttheparameters thatplacethewirematerial intheplasticregion ofthestress-strain curve.Figure5showsadiagram ofthemodel. 234
Radius Drum dwire Li,Arc Length of InsideSurface ofWire L2,ArcLength ofJ Outside Surface ofWiregle ofArc Wire/ / //Ll,Unbent Length/ //z.. Figure5.WireBending Model Aswirebendsaround adrum,itelongates toconform tothedrumsurface. Inthismodel,thewireis assumed tobendaround itsinnersurface ratherthanitsneutralaxis.Thismeansthatinbending thereis onlytensilestressandthatthewiredoesnotstretchorcompress whereitcontacts thesurface ofthe drum.Thearclengthofawrapped segment ofthewire,L,isproportional totheradiusofcurvature, R, andtheangle,o_,sweptbythesegment asshownbelow. L=aR (1) Fortheinsidesurface ofthewire,thearclengthisgivenby Ll=(zRl, (2) wheretheradiusofcurvature isequaltotheradiusofthedrum,RI.Fortheoutside surface ofthewire, thearclengthis L2=a(R1+dw_e), (3) wheretheradiusofcurvature isequaltothesumoftheradiusofthedrumandthediameter ofthewire. Because itisassumed thattheinsidesurface ofthewiredoesnotchange lengthduringbending, thenthe arclengthofthewiresegment afterbending isequaltotheoriginal lengthofthewiresegment before bending. Furthermore, themaximum strainofthewireoccursattheoutside surface. Therefore, the maximum strainofthewire,emax,canbewrittenasthedifference between theinsideandoutside arc lengths divided bytheinitialwiresegment length. Thus,theequation follows fromtheprinciple ofstrain. 235
L2wLt emax= (4) Ll Substituting equations (2)and(3)intoequation (4),thefollowing expression isobtained. a(R 1--I-dwire)-(_l em.x= (5) o:Rj Aftersimplification, themaximum strainofthewire,whichoccursattheoutside surface, is dn,ire em,x= • (6) Rl Sincenostrainoccursattheinsidesurface ofthewire,thentheaverage strain,_,,_)inthewireisonehalf themaximum strain. =d.#_ (7) e,,_,g 2Rl Because thistheoryisverybasic,experimental datawasdeveloped tocorrelate theanalysis. Several versions ofthemechanism weredeveloped andtestedforcomparison totheanalytical performance assessment. Development andResults Construction andTestina FortheISISsetup,testswereconducted withtheControlled deployment deviceinordert0 determine the torque,whichprovides theproperbalance between tubestiffness, deployment rateanddeployment force. Theresultsindicated thattheISIScontrolled deployment devicemustprovide aresistive torqueof6.9Nm.Thisisthetorquethatwasusedasthetargetvalueinthedesignofthewirebrake. Thefirstwirebrakewasbuiltandtestedusingcommercially purealuminum wire.Thealuminum was selected mainlybecause ofitscommercial availability. Highlypurealuminum alsoprovides greater elongation thanaluminum alloys. Indetermining thewirediameter, astrainrangewasselected that bounded thewirediameter range. For1100-0aluminum, theplasticrangeliesbetween strainsof24% and42%.Thisstrainrangewasselected because itisoutside oftheelasticandfailureregions for tempera!uresbetween 21°Cand-100°C.Thetemperature rangewasselected because room temperature andthetemperature atwhichthewirebrakewilloperate insidethecontrolled deployment deviceboundit.Usingequation (7),thewirediameter rangewascalculated forthestrainrange.A supplyandtake-up drumdiameter waschosen as12.7mm.Thisresulted inawirediameter range between 3mmand5.3mm.Thestress-strain curvealsoindicated thattheloadrequired toachieve high strainwouldbesignificantly higheratlowtemperatures ascompared toroomtemperature. Thisindicated thatlowtemperature testingwasrequired. Initially, a3.18-mm diamete(wire wasinstalled intothemechanism. Thetorquethatwasrequired to rotatetheinputshaftwasmeasured as1.92N-m.According toequation (7),theaverage straininthe wireshouldbeapproximately 25%.Although thewirebrakeisdesigned foronlyonebending cycle,the lifeofthedevicewastested. The3.18-mm diameter wirebrokeafter6cycles. 236
Thesecond wirebrakewasbuilttooperate overawiderangeoftorque. Thiswasaccomplished by addinganadjustment rollerthatwouldimpose anadditional bendinthewire.Figure6,showsthesecond wirebreakmechanism. InputShaft Take-up DrurrAdjustment Roller Supply Drurr Figure6.WireBrakeMechanism Asinthefirstwirebrake,thesupplydrum,take-up drum,andadjustment rollerare12.7mmindiameter. Withanadjustment roller,thetorqueiseasilytunedwithout changing thewire.Twoaluminum 1100-0 wiresweretriedintheadjustable wirebrakemechanism; a0.00476 mdiameter wireanda0.00635 m diameter wire.Thetestswereconducted at20°Cand-100°C.Table1showsthetorquemeasured at themaximum andminimum adjustment points. Table1.Adjustable WireBrakeTestResults Wire Diameter [m] 0.00476 0.00635Torque [Nm] 20°Cinl Minimum Maximum Adjustment Adjustment 3.39-3.73 6.78-7.34 12.65-1:_.5(_-100°C Minimum Maximum Adjustment Adjustment 9.72-10.73 18.53-21.47 AsTable1shows,thewirediameter of0.00635 matroomtemperature andwithnoadjustment metthe 6.9N-mtorquerequirement. Because thepropertorquecouldbeachieved bybending thewireonlytwo times,theadjustable mechanism wasabandoned. Subjecting thewireto3bendspresented moreriskof ultimate failurethantheoriginal two-drum designshowninFigure3.Asanalternative, multiple wires werewrapped nexttoeachothertoincrease thetorquefromthatofasinglewirebyafactorofthe number ofwires.Thisalsoreduced theoverallmassofthemechanism. Unfortunately, thepreliminary analysis didnotcorrelate wellwiththeexperimental results. According to equation (7),the0.00635-m diameter wirechosen forthewirebrakeshouldhavefailed.Thecomputed average strainsignificantly exceeded thepublished maximum strainofpurealuminum. Thisindicated thattheprinciple bywhichthewireplastically bendstoformaroundthedrumcouldnotbeapproximated bythesimpletheorypresented here.Morethought isnecessary. 237
Ultimately,adesignwaschosenwhere2wiresfeedacentraltake-up drum.Inthedual-feed device, the wirediameter isonlyhalfofthenecessary wirediameter toproduce thesametorqueonasingle-feed device. Unlikethatofasinglewiredesign, thedual-feed wirebrakemechanism willcontinue toprovide halfthenominal torqueresistance intheeventofasinglewirebreakage. Additionally, thetake-up drum isrelieved frombending because thebending loadsarebalanced byplacing thesupplydrumsin symmetry aboutthetake-up drum.Compared tothesinglewiredesign, theriskoffailurehasbeen reduced inthedual-feed wirebrakemechanism. Conclusion Spaceinflatable structures areshowing promise foryielding largespacestructures withreduced mass andpacking volume ascompared toconventional structures. Animportant aspectofthesestructures is theincorporation ofcontrolled deployment devices toensureaccurate andpredictable deployments. Several mechanisms havebeenproposed forthispurpose, including thewirebrakemechanism, which usesthedeformation ofmetalasamethod ofapplying aretarding forcetoarolledinflatable tube.The development workperformed onthew!rebrakemechanism hasleadtotheconclusion thatthisunique approach toproviding deployment controlforinflatable tubular structures isviable. References Cadogan, D.andM.Grahne. "Deployment Control Mechanisms forSpaceInflatable Structures", 33rd Aerospace Mechanisms Conference, May1999. Cadogan, D.,Grahne, M.,andMikulas M.Inflatable SpaceStructures: ANewParadigm forSpace Structure Design, 49t_International Astronautical Congress, 1998. Sandy,C."NextGeneration SpaceTelescope Inflatable Sunshield Development", 2000IEEEAerospace Conference. March2000. Popov, E.P.Enaineerina Mechanics ofSolids. Prentice-Hall, Inc,NewJersey, 1990. 238
ANovelMechanism usingShapeMemory AlloytoDriveSolarFlapsoftheINSAT-2E Satellite N.Viswanatha* andT.P.Murali* Abstract Aninnovative drivemechanism developed byIndianSpaceResearch Organisation fordeployment and positioning ofsolarflapsissuccessfully wo.rking onthegeosynchronous multi-purpose communication satellite INSAT-2E. Thedrivemechanism 1worksonlinearactuators madeofShapeMemory Alloy (SMA)wiresandiscapable ofdrivingsolarflapsin2-degree steps,likeastepper motor. Thispaper describes thedesignofthemechanism, qualification testingandon-orbit experience. Introduction Thesecond generation IndianNational Satellite, INSAT-2E hasaVeryHighResolution Radiometer (VHRR) aspayload andthepassive coolerofthispayload ismounted onthenorthsideofthespacecraft. Toprovide aclearfieldofviewforthecoolerandtominimize IRheatradiation inputintoit,thesolararray ismounted onlyonthesouthsideofspacecraft. INSAT-2E on-orbit configuration isshowninFigure1.A solarsailmounted onthetipoflongdeployable latticeboomisusedtocounteract theunbalance torque resulting fromthesolarradiation ontheonesidedsolararray.Because ofsun'schanging declination over theyearandconical shapeofthesail,thereisachange intheradiation torqueproduced bysail.Thesail isslightlyoversizedtohavecomparatively highertorqueonsailsideinalltheseasons. Tofinebalance theseasonal residual solarradiation unbalance torque, twosolarflapsaremounted attheendofsolar arrayandtheyareopened/closed toincrease#educe theprojected areaofarraysidetothesolar incidence. Thishelpsinimproved spacecraft pointing andsavingofonboard fuel.  "y  _---IQeIqmut Figure 1.INSAT-2E Satellite on-orbit configuration *ISROSatellite Centre, IndianSpaceResearch Organisation, Bangalore, India. IPatentpending th Proceedings ofthe34Aerospace Mechanisms Symposium, Goddard SpaceFlightCenter,May10-12, 2000 239
Fordrivingsolarflaps,twodrivemotors,basedonlinearactuatorsofSMAareused.TheuseofSMA wasdecidedovertraditionalelectricmotorsandthefinalchoicehasmetallthedesignrequirements with theadvantages oflowermassandcheapercost.Themotorsarealsomagnetically clean. Description ofSolarFlapMechanism Twosolarflaps,Flap-IandFlap-2ofsize980mmx1250mmareconnected totheoutermost solarpanel withtwohingeseach(Figure 2).Eachflapisindependent andhasaseparate SMAdrivemotor mechanism forforward andreverse motion. Whenstowing thesolararraytothelaunchconfiguration, the flapsarefoldedbacktoaposition parallel tothebackside surface ofthelastsolarpanel.Theflapsare heldbysandwiching thembetween thethirdpanelandthelastpanelwithelastomeric snubbers toapply holddownpreloads. Duringthedeployment ofthesolararray,theflapsmovealongwiththelastpanel. Afterthedeployment andlocking ofthesolararrayhinges, theflapsareopened in2°stepstothe required angleusingSMAdrivemotormechanisms. Uptothefirst67.5°oftheiropening, theflapswillbe D<] L.¢: SP-03Stowed flac_:::::=p_ _. -E____ Motordrives -.-_'_--__, Flapdrive I I-lap-z ! hinge Solararray ', .>J + FI?PaCmFeRP .Flapend hinge-t- -t- +underpanelshadow during allseasons. Fromthis position, theflapsare opened farthertothe required anglebasedonthe needtofinebalance the solarradiation torque. Since thedailychange inthe Sun'sdeclination isvery small,theflap(s)needtobe movedbyasteportwoina week.Theflapmovement is donebyground command andeachcommand will moveonestep(-2°)inthe commanded direction. The flapangleisindicated bythe potentiometer builtintothe flapdrivehinge.Eachflap mechanism consists ofone SMAdrivemotor mechanism, oneDrive hinge,andanEndhinge. Theflapsaremadeby bonding twolayersof Kaptonfilm,whichinturnis bonded ontoathinphoto frame-like tubularCFRP framestructure. Figure2.Schematic ofsolarflapdrivemechanism= TheDrivehingeandEndhingeconnect theflapandtheoutersolarpanel.Thedrivehingehasaresistor disc-type anglepotentiometer builtintoindicate theflapangle.Thehinge,asshownFigure3,consists of twobrackets withitsshaftrigidlyattached totheflapsidebracket andthepanel-end bracket isattached tosolarpanel.Thepanel-end bracket isfittedwithaspherical monoball bearing. Theshaftisconnected totheoutputshaftoftheSMAdrivemotormechanism through aflexible shaftcoupling, andthisrotates theflapinstepswhenever themechanism isdriven. TheflapEndhinge(Figure 4),isasimpleidler hinge.Itconsists oftwothinhingebrackets connecting theflapandpanelwithspecified hingespacing. Thepanelsideeye-end bracket isfixedwithaspherical monoball bearing. Amechanical stopisalso 240
provided onthishingetostoptheflapfrommoving beyond 180degrees position. Spherical bearings are usedinthehingestotakecareofanymisalignment between thetwohinges. I--_f ForkEndBracket POT.LeafSpri (CellSide) '_Shaft _-Flap (FullOpen) L FlaPI_ Figure3.Flapdrivehinge -%- _-.-SolarPanel (CellSide) -HingeFixingScrew EyeEndBracket J J_Flap (FullOpen)SolarPanel  (CellSide) EyeEndBracket --_JII-r-MonoBall HingePin--_1_/- Spherical Bearing fForkEndBracket Flap K, Figure4.Flapendhinge 241
Thedetentwheelhas'V'-shaped grooved teethonitscircumference andtheteetharespaced 8degrees apart.Twodetentlevers,placeddiametrically opposite overthedetentwheel,exertloadontothewheel byusingsmalltorsionsprings (detentsprings). Thedetentmechanism alsoprovides theholding torque totheflap,needed tokeepitinthedrivenposition against satellite attitude controldisturbances. Spurqearreducer Spurgearreducer of4:1ratioisemployed toreducethe8degree stepmotionoftheratchetwheelshafttothe2-degree (approx.) stepmotionrequired todrivethesolarflaps.Thegear reducer alsostepsupthedriveoutputtorqueanddetenttorque required attheflaps.Thepinionismounted ononeendofmain shaft,outside thesupport bracket-2 (Figure 6).Thegear, supported ontwobushing bearings, isintegral totheoutput shaft. Load-limiting springmechanism Itisprovided tolimittheloadbuild-up intheSMAwireactuator toacertaindesignlimit,underallconditions ofoperations. Whentheflapsreachendstops,furthermovement offlapsis notfeasible. Ifthedrivemotorisoperated inthisconfiguration, Figure 6.Gearreducer theheated SMAwirecannotcontract toitsfullstrokeasthe assembly onmechanism outputmovement isarrested andhencetheloadinSMAwire wouldbuild-up leading toreduced operating life.Toavoidthis,aload-limiting compression springis mounted atoneendofeachSMAwirewithasetpre-compression (Figure 7).Thisspringdeflects to allowtheSMAwirecontraction whenever theloadintheSMAwireexceeds thesetlimit,thuslimitingthe loadbuild-up inSMAwire. Support Bracket-l-_ iGear_ n_"JHI-I=_Output _E__1_1-[]I_1 ShaftJ mIllBiasSpring _'_ _.i_ Thermal Cover/ Spacer JSupport I Bracket-2 Pawl  _ :m J Wh°°' r..... _LMain Shaft _(t_/_'_ Lk--WireR°Pe _ Ratc.et_ I\ _j'_ Wheel I_-t_'_X "_'-Thermal Cover _.-Pawl Lever--/ Section -BB _--GuidePulley Figure7.SMADrivemotormechanism Inthetransfer orbitofthesatellite, thestacked solararrayispointed tosun.Inthisorientation, thepanel andSMAactuators reachabout1t5°C.Thiswillcausebothforward andreverse SMAwirestoactuate buttheflapsarerestrained frommoving, astheyarestacked. Inthiscase,theload-limiting springs allow SMAwirestocontract andlimittheloadinthemtothesetvalue. 244