ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
SIR-C/X-SAR instruments includingelectronics essentially filltheshuttlepayloadbay.Theprimary objectiveoftheSIR-C/X-SAR missionswastheradarimagingofselect"supersite" targets.SIR-C/XSAR'ssecondary objectives, whichenabledSRTM,includedthedemonstration ofrepeatpass interferometry andscan-SAR. Therepeatpassinterferometry dataisthenusedtorecoverthe topographical featuresofthetargetsurveyed.Scan-SAR isamethodofbeamsteeringthatisthen employedbySRI-M,intheC-band,suchthattheradarswathwidthissufficienttoachievecomplete mappingcoveragein159orbits.SeeRosen,etalforadetailedtreatmentofSyntheticApertureRadar Interferometry. Themodifications totheexistingradarinstrumentrequiredtocollecttheinterferometric dataincludedthe additionofasecondC-bandantenna,a60-metermast,metrology,andadditionalavionics.Further,the GermanSpaceAgencyprovidedasecondX-bandantenna.Thefundamental SRTMinstrument configuration isillustratedinFigure1.Simplistically, SRTMmakesuseoftworadarantennasseparated byafixeddistance,orbaseline,toformafixedbaselineinterferometer. Thein-boardantenna, relative to theOrbiter payload bay,isusedasbothatransmitter andreceiver, whiletheoutboard antenna isonlya receiver. OneofSRTM's significant features istheuseofa60-meter longdeployable mastthatservestodeployan outboard antenna andcreateastablebaseline. The60-meter deployable trussanditsdeployment mechanisms aredescribed byGrossandMessner, 1999.Anillustration ofthevarious components that comprise SRTMisgiveninFigure2.Thestructural dynamic issuesassociated witha60-meter mastand largetipmass,i.e.,theoutboard antenna, deployed fromtheShuttle required significant attention during thedesignandimplementation ofSRTM. Further, SRTMimplemented amastvibration damping system specifically tomeetcertainmastdynamic motionconstraints, aswellastosupplement theOrbiterreaction control system withregardtocontrol system stability. Thetopicofthispaperisthedesignofthemast vibration damping subsystem. Further, themastvibration damping subsystem failedtofunction on-orbit, hencethefailurediagnoses thatoccurred bothduringthemission, andpost-mission arediscussed. Milk! ....:, iF_;,9 Outboard Antenna Bracket ,:_,,- C-To-LDownconverter Outboard Support GP$A_teP,na Structure (OSS) AntennaMAST Antenna Tn.mion (ATS) Outboard AntennaC-Band MainAntenna L-Band MainAntenna Pallet AFT Electronics Panel(AEP) !:: Figure2.SRTMInstrument Component Layout 84
Release Joints(3X) CATForward Bipod -2RigidStruts r' Canister / L,,,,, CATVerticalStrut -Torsional DamperCATAftBipod -1Damper Strut -1RigidStrut CATAxialStrut TSSShearLink(3X) TSS TSSTension Link(3X) Figure3.MastCanister andCanister Attachment Truss(CAT) Thestructural attachment ofthemast,viathemastcanister, totheinboardantenna structure isshownin Figure3;thisstructure wascalledthecanister attachment truss(CAT).TheCATisakinematic, i.e., statically determinate, structure whichservestoattachthemastandthemastcanister totheinboard antenna structure. TheCATforward bipodandtheCATaxialstrutformarigidtripodwithamonoball, or spherical bearing, atitsvertex.Themonoball locatedatthevertexofthisrigidtripodisafixedrotation pointaboutwhichtheentiredeployed mastrotatesasarigidbody.Theattitudeofthemastrelativetoits fixedrotationpointiscontrolled bytheaftbipod,andtheverticalstrut.Themastdamping elements were locatedattheaftbipod,andtheverticalstrut.Thedamping elements locatedintheaftbipodcontrolled the mast'sfirsttwoorthogonal bending modes,whilethedamping element located intheverticalstrut controlled themast'sfirsttorsional mode.Aconceptual modelofthedamping systemimplementation is giveninFigure4. E1 Figure4.SRTMConceptual Dynamic Model NotethattheCATistheonlystructure, whichconnects theSRTMoutboard equipment, i.e.,outboard antenna, mast,andmastcanister, totheOrbiter.Themassoftheoutboard equipment isontheorderof 1340kg(3600Ibm).Hence,theCATwasdesigned tomeetstructural requirements derivedfromlaunch andlanding, i.e.,specificloadsandfrequency requirements. Conceptually itwasacknowledged thatthe 86
damping mechanisms embedded withintheCATwouldberequired tobelocked, i.e.,"stiff",forlaunch andlanding, andunlocked, i.e.,"soft",duringon-orbit operations. RigidLinkPivot -IAxisofRotation TSSSeparation Fitting RigidLink MastCanister Baseplate Damping Cartridges andColocated Spring -3inParallel -pin-ended, flexure hidden Figure 5.Bending ModeDamping Mecanism (CATAftBipod) Vibration Dampinq Mechanism Desiqn Twodistinct damping mechanisms weredeveloped forSRTM. Thebending modedamping mechanism is showninFigure5;thismechanism isalsotheCATaftbipod.Theaftbipodupperstrutisrigidwhilethe lowerstrutcontains threerelatively softsprings andthreeviscous damping elements. Theviscous damping elements aremechanically inparallel withthesprings. Additionally, acaging mechanism is employed tolockoutthesoftsprings forlaunchandlanding. Thetorsional modedamping mechanism is alsotheCATvertical strut.Thetorsional modedamping mechanism issimilar tothebending mode damper, butusesonlyonedamping element ratherthanthree.Thetorsional damping mechanism is showninFigure6. Monoba# Torsional Darnpmg Strut _- _' 7% Monoball ' Separation Joint i MastCanister Figure6.Torsion ModeDamping Mechanism 87
i I° o 0 O 0 -SwitchEs -cutaway -Camagainstclosedstops// ¸¸¸'2 BackView,stop&adaptercutaway -Caminclosedposition i,ii' 04 i.o i7, i',,' ',' IIi,i 2U__/ -PlungerlockedtohousingBackView -Caminopenposition -Plungerunlocked tohousing Figure8.Caging CamConceptual Layout oftheoverall damping mechanism design, thedamping cartridge stifffailuremodewasnotconsidered credible basedonthemitigations described. Ontheotherhand,forthepurposes oftheattitude control system thedamping mechanism stifffailures wereconsidered credible, thisassessment wasbased primary inregardtoforeign objectanddebristypehazards totheoveralldamping mechanism andCAT artriculation. SRTMDampin.q Mechanism Design RecallthattheCATisakinematic (statically determinant) truss.ItisnotedthattheCATaftbipodupper andlowerstruts,i.e.,thebending modedamping mechanism, andthevertical strut,i.e.,thetorsion modedamping mechanism, areaxialforceelements. Thestructural requirements onthesetruss elements aredependent onmission phase.Ingeneral forlaunchandlanding thesetrusselements were required tobestiffandstrong. Thespecific launchandlanding limitloadrequirements were49kN(11,000 Ibf),and120kN(27,000 Ibf),fortheaftbipodlowerstrut,andthevertical strutrespectively. Whileon-orbit thesedynamic impedance requirements implythatthesestrutswereverycompliant. Acommon Iockable linearbearing designconcept wasimplemented forbothdamping mechanisms (Figure 8).Supporting a pistonwithahousing withcamfollower bearings created alinearbearing. Thepistonwaslockedand unlocked relative tothehousing viaacagingcam.Ineffectthecagingcamisadiamond pin.Thecaging camwasactuated bya565N-m(5000in-lbf)DCmotorandgearbox assembly provided byAmerican Technology Consortium. Knowledge ofthelinearbearing statethatis,caged, fullyun-caged, orin determinant, wasprovided byasetoflimitswitches thatwereactuated bymechanical features onthe caging cam.Thelimitswitches usedhereweretheHoneywell 9HMI's. Payload safetyconsiderations leviedatwo-fault tolerant requirement onknowledge ofthecagingcamposition, andhencethelinear bearing status. Therefore, twosetsofthreeindependent switches wereintegrated intoeachcagingcam andactuator assembly, suchthatpositive two-fault tolerant knowledge ofthecaging cain'sposition relative tobeingcagedorfullyun-caged wasprovided. Additional knowledge ofthecagingcamstatuswas inferred viamonitoring ofthemotorcurrent drawduring theactofcaging orun-caging, andthen comparing tosimilargroundtestdata. Alinearpotentiometer wasusedtoprovide arelative displacement measurement foreachofthetwo damping mechanisms. Betatronix, Incprovided thepotentiometer. Thedamper lineardisplacement measurement wasimplemented inordertoprovide additional usefuldataregarding thestateofeach mechanism. Further thedataobtained fromthedisplacement sensorwasconsidered ameasure ofthe dynamic healthofthedevicesincethissensorwassampled attherateof1Hz. 91
Acknowledgments Theeffortdescribed inthispaperwascarried outattheJetPropulsion Laboratory, California Institute of Technology, undercontract withtheNational Aeronautics andSpaceAdministration. References D.Gross,andD.Messner, 1999."TheAbleDeployable Articulated Mast-Enabling Technology for theShuttle Radar Topography Mission," Proc.ofthe33rdAerospace Mechanisms Symposium, NASA/CP-1999-209259, Pasadena, CA,pp.15-30. A.R.Klembczyk, andM.W.Mosher, 1998."Applications ofHermetically Sealed FluidDampers for LowLevel,WideBandwidth Vibration Isolation." Proceedings ofthe69thShockandVibration Symposium. A.Stewart, C.Powers, andR.Lyons, 1998."Improvements forRotaryViscous Dampers usedin Spacecraft Deployment Mechanisms." Proc.ofthe32rdAerospace Mechanisms Symposium. J.Umland, andH.Eisen,2001."SRTM On-Orbit Structural Dynamics," AIAAPaperNo.2001-1588, Proc.oftheAIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics andMaterials Conference, Seattle, WA. 94
•/ FlyCastManeuver forShuttleRadarTopography Mission Thomas A,Trautt" Abstract Theorbitalmaintenance maneuver referred toastheflycastmaneuver wasusedintheShuttleRadar Topography Missiontopreventa60-meter boomsupporting aradarantenna fromvibrating excessively. Thethrusterburnsequence isderivedinthispaper.Analytical resultsoftheboomresponse andactual flightdataarepresented. Introduction TheShuttleRadarTopography Mission(SRTM), whichflewinFebruary 2000,obtained datatomapin threedimensions mostoftheearth'slandsurfacebetween 56°southlatitudeand60°northlatitude. The mission wasajointprojectbetween theNational Aeronautics andSpaceAdministration andtheU.S. National Imagery andMapping Agency withtheJetPropulsion Laboratory serving astheprime contractor. Themainhardware components arethemainantenna mounted inthecargobayofthespaceshuttle,a 60-meter deployable boom,andanoutboard antenna mounted attheendoftheboom.Themainantenna isbotharadartransmitter andreceiver. Theoutboard antenna isaradarreceiver. Radarinterferometry is usedtocompute heightsoftheearth'ssurface. Whiletakingdata,thespaceshuttlewasinadecaying orbitandrequired occasional orbitalmaintenance maneuvers toboosttheshuttlebacktothedesired orbit.Typically, orbitalmaintenance maneuvers consistofasinglepulseofonethruster orseveralthrusters firedsimultaneously fortheduration necessary toboostthespaceshuttlebacktothedesiredorbit.Withthisapproach, thedynamic response oftheSRTMboomcantilevered fromthespaceshuttlewouldnothavehadanadequate marginofsafety. Toreducethedynamic response, afiringsequence wasderivedforasingledegreeoffreedom system. Thederivedfiringsequence isreferred toastheflycastmaneuver. Thefiringsequence consists ofthree pulses.Thefirstpulseputsthecorrectamountofenergyintothefirstmodesothatasecondpulsewhen timedcorrectly willcauseastaticdeflection. Sincethedeflection isstaticduringthesecondpulse,the duration ofthesecond pulsecanbeadjusted withoutaffecting thedeflection. Thecorrecttimingand duration ofthethirdpulsebringsthefirstmodebacktorest. Ananalogy toamultiple degreeoffreedom systemisderived. Theflycastmaneuver derivedforthe singledegreeoffreedom systemisappliedtoananalytical modelofthespaceshuttleandboomand flightdataispresented. Deployable Boom Thedeployable boomwasbuiltbyAEC-Able Engineering. Theboomiscomposed of86collapsible bays andonesolidbayatthefreeend.Thelengthofeachbayinthedeployed configuration is0.6975meter. Inthestowedconfiguration, 85baysarefullycollapsed and1bayispartially collapsed. Thecollapsed baylengthis0.0159meter.Theboomisstowedinacanisterwithamaximum diameter of1.36meters andlengthof2.92meters.Duringorbit,theboomwasdeployed onebayatatimefromthecanister. After thedatawastaken,whichtookabout10days,theboomwasretracted intothecanister, collapsing one bayatatimewhilestillinorbit. AEC-Able Engineering Company, Goleta,CA Proceedings ofthe3_hAerospace Mechanisms Symposium, AmesResearch Center,May9-11,2001 95
Figure9.Portionofdeployed boomviewedfromspaceshuttle Figure10.Antenna andendofboomviewedfromspaceshuttle FiringSequence Derivation Theflycastfiringsequence isderivedforasingledegreeoffreedom modelasshowninFigure11. )_acceleration input spring mass x(t),relative displacement Figure11.Singledegreeoffreedom model 99
Theequationofmotionforthissystemis J_+(o2x=-a (1) wherexisdisplacement ofthemassrelativetothemovingsupport, (0isthecircularnaturalfrequency of thesysteminradiansperunittime,'a'istheacceleration inputatthesupport, andthedotsindicate derivatives withrespecttotime.Thesolution tothisequation withconstant acceleration isgivenbythe following equations. x(t)=-a/_2+(xo+a/o)2)cos(O)t) +(Vo/_o)sin(a)t) (2) v(t)/e)=-(x0+a/e)2)sin((t}t) +(Vo/e))cos(cot) (3) Intheseequations, visrelativevelocity, x0istheinitialrelativedeflection, v0istheinitialrelativevelocity, andtistime.Weassume theinitialdisplacement andvelocity arezero.Attheendofaconstant acceleration pulseofduration, tl,therelativedisplacement andrelativevelocityare Xl=-a/e)2+(a/e)2)cos((_l) (4) vl/o)=-(a/e)2)sin(e)tl) (5) Turning thepulseoffforaduration, t2,aftertheinitialpulsewillresultinthefollowing relative displacement andrelativevelocityattheendofthet2duration. x2=xlcos((._2) +(vjo.))sin(e)t2) (6) v2/o)=-xlsin(fJ}t2) +(vl/r3)cos((tX2) (7) Fromthesetwoequations, thefollowing equations canbeobtained. x2sin(O_2) +(v2/(J))cos((l}t2)= Vl/O_) x2cos(03{2) -(v2/OJ)sin((J}t2) =Xl(8) (9) Applying another pulseattheendofthet2duration resultsinthefollowing response ofthesystemduring thepulse. x(t)=-a/(t)2+ (x2+a/o)2)cos( e)t)+(v2/(o)sin(e}t) (10) Forx(t)tobeconstant, thefollowing conditions mustbesatisfied. x2=-a/(_ (11) v2=0 (12) Substituting equations (4),(5),(11),and(12)into equations (8)and(9)andcanceling someterms,we obtain sin((tX2)=sin((t}{1) (13) cos((£t2) =1-cos((t}tl) (14) 100
Thesolutiontotheseequationswiththeshortestdurationoftimeisasfollows. 0._1=03t2=/I;/3 tl=t2=(_:/3)(1/0))=(_:/3)(T/2/t) =T/6(15) (16) Inthelastequation,Tisthenaturalperiodofthesystem.Attheendofthemainpulseofarbitrary duration, t3,therelativedisplacement andrelativevelocityare x3=x2=-a/_o2 V3=v2=O(17) (18) Thepulseisturnedoffforaduration, t4,andonagainforaduration, t6,resulting inthefollowing relative displacements andrelativevelocities attheendsofthet4andt5durations. x4=X3COS(0./L4) =(-a/e)2)cos((t)t4) (19) v4/CO=-x3sin(o._) =(a/o)2)sin(eY,4) (20) x5=-a/ct_+(x4+a/o)2)cos(Cots) +(v4J(o)sin(Cot5) (21) V5/(0=-(x4+a/(j)2)sin(O.}ts) +(v4/(O)cos(O3t5) (22) Combining equations (21)and(22),thefollowing equations canbeobtained. x_sin((t}t5) +(v5/(..t))cos((t}t5) =v4/(.o-(a/o.)2)sin(cet5) (23) xscos(o_ts) -(Vs/(.0)sin((t}t5) =x4+alo_-(a/(.02)cos(oY5) (24) Attheendofthet5duration, wewantthesystemtoreturntozerorelativedeflection andzerorelative velocity. Settingx5andv5tozeroresultsinthefollowing equations. 0=v4/O)-(a/O)2)sin((..Q:5) (25) 0=x4+a/O._-(a/Co2)cos((t_5) (26) Theseequations arecombined withequations (19)and(20)toobtainthefollowing equations. 0=sin(crY4)-sin((ot5) (27) 0=cos(cot.4) +1-cos(o_5) (28) Theseequations aresimilartoequations (13)and(14).Thesolutionwiththeshortest duration is t4=t5=T/6 (29) Figure12showsthepulsesequence andresponse ofasingledegreeoffreedom systemwitha0.1Hz naturalfrequency. Theresponse toasinglepulseisshowninFigure13forcomparison. Theresponse to asinglepulsehastwicetheamplitude oftheresponse totheflycastpulsesequence. 101
f l flycastpulse sequence 0 -1_\\relative deflection/ _ 0 i0 20 _e.(sec) Figure 12.Flycastsequence andresponse ofsingledegree offreedom system (normalized tostaticcondition) _I I -2 r_lai_ve deflection I I o tot_ne,(sec)20 3o Figure13.Singlepulseinputandresponse ofsingledegree offreedom system (normalized tostaticcondition), Thefiringsequence wasderived forasingledegree offreedom without damping. Theerrorfrom neglecting damping isanalyzed below. Theequation ofmotionforthesingledegree offreedom with damping is +2(,(0_"+(02x=-a where_isthedamping ratioandeL)istheundamped natural frequency inradians perunittime.The relative displacement andrelative velocity responses aregivenbythefollowing equations. [a]]V0+_X0---- '_ 0.) +(02 __aJc°s((0dt )+ sin((%t) (30)+(02 1___2  _Ia]1v(t)__(0t x0+,_v+vo---e- --cos((%t) + sin((0dt) (31) 102
where o)d=_-42e_ (32) Thedamping ratioofthefirstmodeoftheboomisapproximately 0.005.Applying thefiringsequence toa singledegree offreedom system withthisdamping ratioresultsintherelative displacement profileshown inFigure14.Themaximum deflection magnitude is0.89%greater thanwithout damping. Thiserroris similartotheamount ofdecayofadamped system overaperiod,T/3,asfollows. 1-e-((°t=1-e-(O'O05)(2=/T)(T/3) =0.0104 =1.04% (33) 0._I 00 ".it -05 ¢) "-_-1I I -1.5 I I 0 10 20 30 (sec) Figure14.Response ofdamped system toflycastsequence (normalized tostaticcondition), Multiple Degree ofFreedom Analogy Neglecting damping, amultiple degree offreedom system canbemodeled inthefollowing form. M._/+K-x =B.f (34) Inthisequation, Misthesystem massmatrix, Kisthesystem stiffness matrix,xisavectorofdegrees of freedom, Bisaloading matrix, andfisavectorofforcing functions. Thevector, x,canberelated tothe modalamplitudes, u,bytheequation, x=@u, (35) wherethecolumns of@areeigenvectors ofthesystem. Theeigenvectors arenormalized withrespect to themassmatrixtoobtainthefollowing resultwhereIistheidentitymatrix. (]DTM(_ =I (36) Substituting equation (35)intoequation (34)andmultiplying by@'rresultsinthefollowing equation. I.ii+E_.u =_TB.f (37) 103
where (38) Thematrix,f_,isdiagonal andthediagonal termsaresquares ofthenaturalfrequencies ofthesystem. Inequation (37),themodalamplitudes areuncoupled fromeachother.Theequation formodeicanbe writtenasfollows. iii+(0.2.ui=(_TB. f)i(39) Thisequation isanalogous toequation (1)forthesingledegreeoffreedom. Bytuningthefiringsequence toaparticular mode,theresponse ofthatmodewillbesimilartothesingledegreeoffreedom response inFigure14. Analytical Results Theboomcoordinate systemandorientation oftheboomrelativetothespaceshuttleareshownin Figure15.Afiniteelement modelisshowninFigure16. •-'::;'??...... :'-'-:_-cC Y 14° Z Figure15.SpaceShuttleandboom 104
antenna modeled with__ beamelements SpaceShuttlemodeled as _1_ pointmass"¢_thmer'aa 7 '__ beam2°md:l_ with stiffbeams':____ Figure16.Finiteelement model Thelowestnaturalfrequency fromthefiniteelement modelis0.1Hzduetobending oftheboomabout theZaxis.Thismodeisthemostaffected bythethrusters usedfororbitalmaintenance. Theperiod,10 seconds, ofthefirstmodeisusedtocompute theflycastpulsesequence forthefiniteelement analysis. Thepulsedurations onthespaceshuttlecanbeadjusted inincrements of0.08second. Tocompute the worstcaseresponse accounting forthetimeincrements ofthethrusters, durations of0.08secondare addedtotheshortpulsesandtothedurations between thepulses.Theshortpulseduration forthefinite element analysis isthencalculated asfollows. shortpulseduration =(10sec)/6+0.08sec=1.75sec Thefiringsequence appliedtothefiniteelement modelisasfollows. onfor1.75sec offfor1.75sec onfor13.0sec offfor1.75sec onfor1.75sec Theboomtipdeflections duetothefiringsequence areshowninFigure17.Thebending moments atthe rootoftheboomareshowninFigure18.Thebending strength oftheboomis9200N-m.Thetwo bending moments combined willmeettherequired safetyfactorof2.0. 105
0.1 0.0 -0.3ax,in sA2)I  I uz,(m)i =L-- ux,(m) i i i 0 5 10 15 20 25I time,(sec) I ..... J Figure17.Boomtipdeflections andspaceshuttlex-acceleration '! l 1000..................................................................................................................................................................................... i' o ! -1000 -2000 -3000 -4000 .... 0 5 10 15 20 25 time,(sec) Figure18.Boombending moments andspaceshuttlex-acceleration FlightResults Duringorbit,thefirstnaturalfrequency oftheboomwasmeasured priortoapplying theflycast maneuver. Theperiodforthefirstnaturalfrequency was10.53seconds. Asmentioned intheprevious section,thepulsedurations canbeadjusted inincrements of0.08second. Dividing theperiodby6and rounding tothenearestmultipleof0.08secondresultsinaduration of1.76second. Thisduration was usedfortheshortpulsesanddurations between pulsesintheflycastmaneuver. Boomtipdeflections scaledfromcamerascenestakenduringaflycastmaneuver arecompared withthefiniteelement results inFigures19and20.Theflycastmaneuver startsattime,1.0second, intheplots.Theactualdeflections aresimilartothedeflections obtained fromthefiniteelement model. 106
v0.1 ._o"50.0 -0.1 × -0.20.3 t 0.2............... H E !  [--finiteelement] ___.__i ..... ...... -0.3 , 0 5 10 15 20 25 time,(sec) Figure19.Boomtipxdeflections duringflycastmaneuver 0.3.......................................................................................................................................................................................... 0.2 Ev0.1 tO _=0.0o -0.1 N -0.2,[finiteelement 1 actual ! -0.3 0 5 10 15 20 25 time,(sec) Figure20.Boomtipzdeflections duringflycastmaneuver Conclusion Thetypicalsinglepulseorbitalmaintenance maneuver wouldhaverequired theboomtoberetracted beforeeachmaneuver. Theboomtakesabout20minutes toretractand20minutes todeploy.Usingthe flycastmaneuver, theloadsontheboomwerelowenoughthattheboomdidnothavetoberetracted priortothemaneuver andallowedmoretimefortakingdata. Acknowledgments Theauthorwouldliketoacknowledge BillLayman fromJPLforsuggesting thatapulsesequence could befoundtodeflecttheboominastaticdeflected shapesimilartoflycastingafishingpole. 107
Development of"Super-Flat" StrainWaveGearing Yoshihide Kiyosawa*, Yoshihiro Tanioka* andKeijiUeura* Abstract Strainwavegearing, alsoknownasharmonic drivegearing, hasbeenusedinmanyspaceapplications wherelightweight andcompact mechanical components areessential. Tomeettheserequirements, anew typeofstrainwavegearing, the"Super-flat" component setCSD-type, hasbeendeveloped. Therewere manyissuestoberesolved inordertorealizethesuper-flat design. Newideasandnewtechnologies were applied todevelop CSD-type gearing. Itsexceedingly flatshapehasneverbeenseenbeforeinaprecision speedreducer. Thisnewgearwillallowanewgeneration ofsolararraydrivesandantenna pointing devices tobedeveloped. Introduction Strainwavegearing hasbeenusedinmanyspaceapplications sinceitwasfirstdeployed ontheApollo15 mission 30yearsago.Solararraydrives,antenna-pointing devices androbotarmsareotherexamples. In spaceapplications, lightweight andcompactness areessential. Theserequirements ledtothedevelopment ofanewtypeofthestrainwavegearing, the"Super-flat" CSD-type component set. Development toreduceaxiallengthhasbeencontinuing foraquitesometime.In1991,a40%reduction of theaxiallengthascompared totheconventional typeofstrainwavegearing CS(orHDUC)-type was developed. TheCSF(orHFUC)-type gearwasintroduced tothemarket. TheCSF-type gearalsoemployed anewtoothprofile("S"toothprofile)andanewdiaphragm shape,whichcanachieve increasing torsional stiffness andtorquecapacity. Itallowed thepossibility todesigncompact spacemechanisms. Now,the CSD-type gearhasbeendeveloped, usingalsothetechnology of"S"toothprofileandnewdiaphragm shape,toreducetheaxiallengthevenfurther. Thispaperwillpresent thedesignmethods forthesuper-flat harmonic drivegear. CS-type CSF-type CSD-type Figuret.Cup-type strainwavegearing Harmonic DriveSystems, Inc.,Hotaka-machi, Minamiazumi-gun, Nagano, Japan Proceedings ofthe35thAerospace Mechanisms Symposium, AmesResearch Center,May9-11,2001 109