ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Figure7.Magnet degradation Theflexdiskdiaphragm wasanalyzed withtheANSYS finiteelement program. Anon-linear large displacement analysis wasperformed, resultsofwhichindicated thatthemaximum stressattheareaof failureis324MPa(47ksi)(Fig.8&9).Brush-Wellman wascontacted formaterial properties ofthe C17200 SN-TD01 solution-treated +cold-worked beryllium copperalloy.Sometypicalproperties: Endurance limit: 230MPa(33.350 ksi) Allowable stress: 214-248MPa(31-36ksi),R=-I,108CyclesReverse Bending Figure10isthemodified Goodman diagram fortheberyllium copper alloy.Fatigue strength forcopper alloysisusually defined asthestresssustainable without failurefor1000millioncycles. Fortheaverage (50%)curves, thisactually meansthat50%willfailatthisstresslevel. Maximum loading MaxPrincipal Stress --47.6KSIANSYS 5.5.3 JtFN 182001 13:14:00 NODAL SOLUTION STEP=2 SUB=10 Tiff=2 Sl (AVG) TOP 1)t.r_.X=.0:37614 S_:';=47.553 X_.I=-.64.5E-08 7V=-.86602S ZV=.S DIST=I.303 XF=-,124E-04 YF=-.322E-03 ZF=-.280716 Z-BUFFER 0 _ 528410567  1585121135 _ 26419 31702 _ 3698642270 [RE] 47553 I4UDER FSM Figure8.Non-Linear FEMAnalysis Results-Principal StressvsApplied Force-,Max.Displacement NASA/CP--2002-211506 211
FSMFlexure Disk Maximum Stress 45000 40000 35000 30000 (ps25000,vo nM ise  20000 15000 10000 5OO0 0 0 8Oi .I SAG LOADI t I.......i i 2 4 6 8 10 12 14 16 LoadStep Figure9.Stressversus Applied Load FSMFlexFlexure Diaphragm Fatigue Modified Goodman Diagram Sy70 E 00 ,,,,60 i (D "(D  50 {::}.. K <I: co40co "¢ 1DOFDeflection saSe °l- vqn .25DegDeflection  2DOFDeflection Sa' _ !.25DegDeflection20 Modified Goodman Line 10 _ rties° C .............. 010 20 30 40 50 60 70 Sm Sin' Syt Stress-KPSl Mean80 90 Sut JTW/1 8/14/01 Figure10.Modified Goodman Diagram forBeCu NASA/CP--2002-211506 212
Conclusions Analysis resultsindicated thatinspiteofitssimplicity, lowestcost,andminimum partscount,theflexure diskdiaphragm presents thefollowing performance limitations: 1-Finitefatiguelife 2-Mirrorsurface figurecompromised duetobending. Thiswascaused byplacing themirrorintheload path. 3-Excessive crosscoupling provedtobedetrimental toservocontrol 4-Highpowerconsumption resulted inexcessive heating. Several design alternatives wereconsidered. The following isasummary ofdesigntrade-off studies: DesignAlternative 1-Dual-Axis gimbalusingflexpivotbearings (Figure 11) Thisapproach offers: 1-Atruegimbaldesign 2-Rotation axesarecoplanar andcompletely decoupled 3-Infinitefatiguelifefor63°rangeofmotion 4-Stablemirrorplatform 5-Minimal powerconsumptionFigure11.Dualaxisgimbal withflexpivots DesignAlternative 2-Metalflexuredesign(Figure 12) 1-Design offersmodular approach 2-Canbesizedfordisplacement andlife 3-Stablemirrorplatform 4-However thisapproach requires axialvolume, itis moreexpensive, itmaypresent modalcross coupling, andmaypresent highpower consumption. Figure 12.MetalFlexure Design DesignAlternative 3-Lord®Miniature Mount MAA001 Series(Figure 13) 1-Simple 2-Rugged 3-Easyassembly 4-Inexpensive 5-Stablemirrorplatform 6-Maycreatedamping effects, finitelifefor elastomer, finiteshelflife,temperature affected properties -stiffness, life,outgassing (mirror clouding) Figure13.LordMiniature Mount NASA/CP--2002-211506 213
Basedontheforegoingtrade-offstudies,itwasdecidedthatthetrueflex-pivotgimbalisthebestfollowoncandidatefortheFSM,sinceitoffersamorestablemirrorplatforminabsenceofmodalandcross-axis coupling,andforitslowpowerconsumption. Theelastomeric flexurebaseconceptsarelessattractive duetolifedegradation issues,modalandcross-axiscoupling,stiffnessvariabilityandoutgassing issues. Thedesignwasmodifiedtoincorporate theflex-pivotgimbaldesign.Flex-pivotbearingsarefrictionless, stiction-free bearingsuniquelysuitedforlimitedangletravelapplications, suchasinthecaseoftheFSM. Flex-pivots requirenolubricationandprovideinfinitelifeforlimitedtravelrange.Theyprovidehighradial andaxialstiffness,lowhysteresis, exceptional repeatability, predictable performance andelectrical continuity.Thelackofanyneedforlubricationprovidesforoperationinhardvacuumwithoutthedanger ofspacewelding,andproblemsassociated withverysmallangularditheringmovements inherentin conventional ballbearings. Themagneticdesignwasmodifiedforrelativelyconstantairgapandthedesignwasoptimizedfor materials,geometryandthickness. Anaccelerated lifetesthasshownthatthedesignoftheFSMisruggedandstructurally soundforits intendedlifeexpectancy. TheFSMwasexposedto64,000cyclesatfullrangetravelof62.0degrees.In itsintendeduse,theFSMwouldonlyexperience afractionofthisfullrangecycleoveritsintended lifetimeof15years. Theopticalmountandthemirrorattachment wereoptimizedtomaintaintheopticalfigurebetterthan2.5?, @632.8nmwavelength fortemperatures of0to60degreesC.Themirrorisbondedatthreelocationsto themirrormount. Thedriftproblemsinherentininductivesensorsweresolvedbyreplacingthemwithopticalsensors.The accuracyandrepeatability oftheFSMiswithinthe1microradian specification, asdemonstrated above. FuturePlans Asisthecasewithmostelectromagnetic designs,thereisverylittlepassivedampingintheopen-loop device.Morethananyotherfactor,thismakesitdifficulttoachievehighbandwidthwithoutsacrificing stability.FutureFPMdesignswillinvolveamirrorplatformwithhigherpassivedampingandconsequently higherbandwidthandbetterstabilitymargins. Thecurrentpowerrequirement ofthemechanism foroperationatthemaximumangularrangeof2.6 degreeis0.250A.Themechanism dissipates lessthan1.0wattofpowertomove2.6degrees ineitherthex-ory-axis,notincludingthe electronics. Thegoalisacompletesystempower._ dissipation oflessthanonewattforoperationati.::_: anamplitudeof2.6degrees. _:..::.: Ultimately, theFSMabilitytosurvivelaunch vibrationsandoperatinginthespaceenvironment mustbedemonstrated. Astheelectromagnetic designisofthesamebasictechnology asmany othermechanisms usedinspace,nosignificant problemsareexpected.Althoughthestructural analysisperformedontheFSMindicatesthatthe currentdesigniscapableofsurvivingthe spaceflight launchenvironment andsubsequently operating,fullqualification testingisplanned. Figure14.Modified FSMunit NASA/C P--2002-211506 214
ADescription andPerformance ofMechanisms usedinthe HighResolution Ionospheric Thermospheric Spectrograph PhillipKalmanson*, HsiungChou**, Russell Starks*, Kenneth Dymond ÷,andStefanThonnard ÷ Abstract TheHighResolution Ionospheric Thermospheric Spectrograph (HITS), builtbytheThermospheric and Ionospheric Physics Section oftheNavalResearch Laboratory, wasdesigned forflightaboard the Advanced Research andGlobal Observation Satellite (ARGOS). HITSwasoneinstrument inan aeronomy threesensorsuiteknownastheHighResolution Airglow andAurora Spectroscopy (HIRAAS) experiment. Thedevelopment oftheHIRAAS instruments wasalowcost,rapidprototyping effort. ARGOS wassuccessfully launched intopolarorbitfromVandenberg AirForceBaseonFebruary 23, 1999andcontinues initssuccessful operation atthetimeofthiswriting. TheHITSinstrument isaoneaxisgimbaled spectrometer operating inthefarandextreme ultraviolet. HITSusesfiveseparate mechanisms initsdesign. Eachofthesemechanisms wasdesigned inorderto address specific issues affecting theHITSinstrument ranging fromoptical system operation, data acquisition, launch, andcontamination control. Whatfollows inthispaperisadescription ofeach mechanism andtherequirements theyweremeanttofulfill,theproblems encountered duringmechanism construction andtheirsolutions, andtheoverallcostandeffortinvested ineachmechanism. HIRAAS isa goodexample ofevaluating thetradespaceforriskandperformance tominimize development costand time. Instrument Overview TheHighresolution Ionospheric Thermospheric Spectrograph isanaeronomy instrument designed to observe theionosphere byviewing theearth's limbfromlowearthorbit.Theoverall design ofthe instrument didnotallowforredundancy, however allpossible singlepointfailures wereevaluated against theimpacttomission objectives. Whenfeasible, alternative orbackup systems wereemployed. Since weightwasnotacriticaldesign parameter, areduction incostanddevelopment timewasachieved by using6061-T6 aluminum formostparts.TheHITSinstrument isshowdinFigurE: 1without isthermal blankets. Thefiveseparate mechanisms integral tothedesignofHITS,are;thedustcoverdoorassembly (DCDA), thegimbalcagingmechanism (GCM), theone-axis gimbal, thegratingdrivemechanism (GDM), andthedetector doormechanism (DDM). Thelocation ofeachmechanism isshowninFigure2.The opticaldesignandtheobjectofinterest whichistheearth's limbfromLEO,arewhatdrivetheneedfor havingtwoofthefivemechanisms inHITS,thesemechanisms arethegrating driveandtheoneaxis gimbal. Boththeone-axis gimbalandthegratingdrivewereessential forsuccessful operation andwere designed tooperate continuously fortheone-year lifetime. TheDCDAandtheDDMwillnotbediscussed inthispaperhowever theGCMwillbementioned asitrelatestothegimbalstructure design. PraxisInc.Alexandria, Virginia **Atlantic Online-Formerly withRaytheon STX,Lanham MDattimeofHITSDesign +NavalResearch Laboratory, Washington D.C. Proceedings ofthe36thAerospace Mechanisms Symposium, Glennresearch Center,May15-17,2002 NASA/CP--2002-211506 215
Figure 1.HITSInstrument Figure2.HITSMechanical Component Layout TheGrating DriveMechanism TheopticaldesignoftheHITSinstrument isdescribed asanf/5.41-meter Rowland CircleSpectrograph withanin-plane Eaglemount. Attached tothespectrograph is1/8meteroff-axis parabolic telescope 1. TheHITSinstrument isdesigned tohaveapassband inthefarandextreme ultraviolet (FUVandEUV respectively) of500-1500 angstroms witharesolution of>0.5angstroms. Anunderstanding ofthe Rowland circlespectrograph principles isneeded todefinethesatisfactory performance oftheHITS GDM. ARowland circlespectrograph operates undertheprinciple thatforaconcave grating, minimal aberrations occurwhentheentrance slitofthespectrograph andthedetector lieonacircle.TheRowland circleisdefined asacircleofadiameter equaltothetangential radiusofthegrating. Atdifferent locations alongthiscircle,theimageofthevarious wavelengths isfocused. HITSasanin-plane Eaglemount NASA/C P--2002-211506 216
designmeansthattheentranceslitandthedetectorlocationsarefixed.Inordertopositiondifferent wavelengths onthedetector,thegratingmustberotated.Whiledoingso,thegratingmustalsobe translatedsuchthattheentranceslitandthedetectorbothremainontheRowlandcircleascanbeseen inFigure32. Grating ........ Entrance slit \...., V............Rowland circlel l Plate , l / .. .. _ Figure3.Operation ofanEaglemountRowland circleSpectrograph Grating DriveMechanism Desiqn TheGrating DriveMechanism (GDM)designdirectly affectstheimagequalitywithregardtofocusand comaaberrations. Therefore thedesignoftheGDMmustbeindividually tailored totheopticalsystem in whichitused,specifically thegratingdetermines theperformance requirements andareasfollows: •Provide twodegrees offreedom forthediffraction grating, onerotational andonetranslational. •Provide 100mmoftotaltranslation with0.10-mm accuracy. •Provide 25degreetotalrotation with0.2degree accuracy Theoriginal design oftheGDMshowninFigures 4and5involved theuseofaballscrewactuated translation stagedrivenbya14mN-m(2oz-in)stepper motorwith100:1harmonic drivegearreducer. Thetranslated portion ofthestagecontained aseparate butsimilarmotorandharmonic drivetoformthe rotation stageontowhichthegrating housing wasmounted. Supporting therotation stageweretwo guiderailscomposed ofashaftmounted onaT-bracket. Therotation stagewasattached totheguide railsbyfourthree-quarter encircling linearballbearings, twooneachrail.Thedesignoftherotation stage allowed thegratingtomove5degrees beyond therequired 25degrees. Sincetherelationship between therotation andtranslation ofthegrating determines theimagequality, a SlotandFollower Camwasruledoutduetolackofinflightflexibility. Additionally concerns about changing performance duetowearandthermal variation emphasized theneedforinflightcorrections. By decoupling theindividual degrees offreedom intheGDM,animagefocusing capability isgained by translating thegrating alongtheopticalpath.Thiswasagooddecision sincetheoriginal grating hadtobe replaced duetopooropticalperformance. Theoriginal grating rulingdensity was5000linespermmwith ablazeangleof834Angstroms. Duetoschedule constraints, areplacement grating couldnotbe manufactured intime.Asaresult,agrating witharulingdensity of3600linespermmand1200 Angstroms blazewasinstalled forflight.Ifaslot/follower orcammechanism hasbeenusedthe replacement grating wouldhaverequired modifications. NASA/CP--2002-211506 217
Restraint LeadScrew Notch &Pi Antibacklash _,_ Nut1NUt/  _-_, Stepper /_otor ;r=q Ig:,,'_,=;__,®3i//1/ I!--I Limit L,:__ ,4__::__) hes  w,tcSwitch .................... Grating Mount / Rotation Stage Figure4.GDMTranslation StageLayout TopView Harmonic Drive Stepper Motor Figure5.GDMRotation StageLayout FrontView Testinq, Failures, andRedesigns Testing doneontheoriginal GDMexposed threeflawsthatrequired aredesign. Theflawsthatwere discovered involved thetranslation driveassembly, therotation stagesupport rails,andtherestraint mechanism. Insolving eachflawasolution thatinvolved theminimal amount ofreengineering ofthe original method ofoperation wasnecessary duetoschedule constraints. Alloftheseflawsweresolved through thesubstitution ofamodified partinplaceoftheoldone. NASA/CP--2002-211506 218
HITSOne-Axis Gimbal Theuseoftheone-axis gimbalwasdrivenbythevertical sizeoftheregionofinterest intheLimb,the desired resolution ofthefeatures tobeobserved, andthefieldofviewoftheinstrument. Thelimbregion ofinterest extends fromaltitudes of100-750 kmabovetheearth's disk.TheHITSfieldofview(FOV)is 0.06degree inthevertical direction and4.6degrees inthehorizontal. TheFOVtranslates tospatial resolution of3kmX230km.Tobeabletoscanacrossaltitudes of100-750 kmagimbalwasneeded as showninFigure6.Thisgimbalrotated theHITSopticalbenchaswellastheIonospheric Spectroscopy andAtmospheric Chemistry sensor (ISAAC) showninFigure7.ISAACwasanother separate, coaxially aligned instrument mounted ontothesideofHITS. D ""':'_i_"______ 30°Exlended ...."=-:.:--.:.:.--.......... Scan 17°Normal --:-::::---:---.___ ........... Stall _750 kn_ Figure6.One-axis Gimbal rangeofmotion Ordinarily acheaper andsimpler approach toscanacrossafieldofregardistouseascanmirrorrather thanscanning awholeinstrument. Unfortunately thenatureofopticsintheFUVandEUVprevent the addition ofanother mirrorduetotheextreme losseseachopticalelement causes. Current losesof60 percent perreflection aretypicalintheEUVwavelength rangesofinterest. Optimizing thelightthroughput fortheEUVwouldreducethethroughput fortheFUVtounacceptable levels.Theadditional thirdsurface ofascanmirrorwouldresultina90percent totalattenuation ofanalready weaksignal.Furthermore, by usingagimbal theoverall timeforinstrument development wasreduced inthatboththeoptical subsystem andgimbal subsystem couldproceed independently inbothconstruction andcalibration. A scanmirrorwouldhaveprevented theinstrument frombeingcalibrated untiltheintegration ofthescan mirror.Additionally, morecalibration stepswouldbeneeded todetermine theeffectofthescanmirror angleontheoptical performance. BeingabletousetheHITSgimbaled platform alsoshortened the development andcostoftheISAACinstrument. Thegimbaled HITSopticalbenchprevented ISAACfrom needing another mechanism toscanacrossitsfieldofregardandonceagainallowed forindependent opticalsystem development andcalibration. NASA/CP--2002-211506 220
Figure7.ISAAC Instrument mounted onHITSgimbaled optical bench Thisapproach ofusingonescanplatform forseveral instruments wasalsousedinanother instrument builtbyNRLwhichwasknownastheRemote Atmospheric andIonospheric Detection System (RAIDS). RAIDScontained eightindividual sensors mounted onacommon frameattached toaone-axis gimbal. Gimbal Desiqn TheHITSgimbalhasseveral uniquequalities flowing fromtheconstraints uponit.Thewideopticalpath ofthespectrograph negated theuseofashaftmounting thecamera tothegimbal. Theenvelope constraint ontheinstrument required thegimbal rotation axistobeoffsetfromthecamera centerof gravity. Also,budget constraints madetheusethenon-flight qualified partsanattractive alternative. In designing thegimbalthefollowing requirements hadtobesatisfied: •Provide asingeaxisofrotation fortheinstrument opticalbench •Provide a17degree nominal scanfrom-10to-27degrees withrespect tothespacecraft horizon beingequalto0degrees •Provide a30degree totalscanfrom-10to-40degrees withrespect tothespacecraft horizon being equalto0degrees. •Provide a0.1degree scanwindow. •Perform anominal scanoftheHITSopticalbenchin90seconds (0.189degree/sec) •ReturntheHITSopticalbenchassembly tothestarting position in15seconds (1.13degrees/sec) TheHITSopticalbenchandISAAChadaresultant gimbaled massof36.8kgandaninertiaof7.45kgm2.Thegimbaled masscenterofgravity wasoffsetfromtherotation axisby27.3cm.Minimizing the transfer ofuncompensated angular momentum fromthegimbaloperation wasnotanissueingimbal design. Communication withtheARGOS spacecraft designers duringspacecraft designresulted inthe spacecraft beingconstructed withmomentum wheels sizedtocounteract theexpected transfer ofangular momentum. Thegeneral design oftheHITSgimbal involved supporting theoptical benchontwosidesbytwo separate support pillarsmounted toacommon baseplate. Thedrivesystem andposition feedback system weremounted insideopposite pillarsandsupported independently fromthemaingimbalbearings inordertodecouple theloadpathfromthedrivesystem. DriveSystem Themaingimbal bearings consisted of125-mm innerdiameter crossed rollerbearings fromthe Messinger Bearing Corporation. Crossed rollerbearings werechosen duetothevolume constraints that wouldhavebeenviolated inproviding forthepreload springs inmoretraditional ballbearings. However, NASA/C P--2002-211506 221
usingtheserollerbearingsincreasedtheamountoftorquedeliveredbythedrivesystemduetothe higherfrictionascomparedtoballbearings.Thelargesizeofthebearingswaschosensothatitwouldbe abletofitaroundmuchofthedrivesystemasshowninFigure8. : Stepper • Motor,..,Input Shaft Figure 8.HITSGimbal DriveAssembly Component Layout Thedrivesystem, showninexploded viewinFigure9,consisted ofastepper motorthesameastheone usedintheGDM.Thestepper motoroutputwascoupled toaninputshaftbyaspurgear.Thisprovided a firststageofgearreduction by7:1.Theinputshaftwassupported byitsownsetofbearings andwas directly coupled tothewavegenerator ofaHDSystems harmonic drive.Theharmonic drivehadagear reduction of160:1andwasmounted withthecircular splineasthestationary component. Theflexspline outputwasdirectly coupled tothegimbaloutputhubbyaclampringthatalsocontained oneoftheinput shaftbearings. Thegimbalmountwasthenboltedontotheoutputhub.Aharmonic drivewaschosen for thisgimbalduetoitssimplicity, itshigherloadratingascompared toaplanetary gearbox ofthesame physical size,anditsfeature ofzerobacklash. Although thereisaminorsourceofbacklash inthestepper motortoinputshaftcoupling, itsaffectafterthe160:1reduction isnegligible asfaraspositional accuracy 3. NASA/C P--2002-211506 222
Figure9.HITSGimbal DrivetoStructure Component Layout Encoder System Position sensing intheGimbal wasaccomplished byusingavacuum ratedencoder fromBEI Technologies. Inc.Theencoder wasmounted independently fromthedrivesystem insidetheopposite support asshown inFigure10.Motion ofthegimbaled opticalbenchispassed toencoder though a flexible shaftcoupling. Thisdirectcoupling negates anyerrorsinpositional accuracy fromdrivesystem losses. Asource oferrorthatthisencoder mounting system doesnotaccount forisduetodistortions fromthermal expansion. Figure 10.HITSGimbal Encoder Assembly Component Layout NASA/C P--2002-211506 223
Theseerrorsmayarisefromdifferentialheatingoftheseparatesupportpillarsandfromanydistortion causedbythemountingofthesteelrollerbearingsinsidethealuminumsupports.Fortunately, these errorsarewithintheallowablespecifications forinstrumentaccuracy. Structure TheopticalpathinsidetheHITSinstrument prevented theuseofashaftforthegimbal, asitwouldhave interfered withlighttraveling fromthegrating tothedetector. Rather thanmountthegimbal tothe instrument cowling, aboxdesignwaschosen asthemainstructural support linkingtheopticalbenchto thegimbalassembly asshowninFigure11.Thisgimbalanchor boxwouldprovide thestructural support necessary whilenotinterfering withtheoperation oftheinstrument 3. Figure 11.Original HITSCamera Structural Layout Unfortunately, resultsfromfurtheranalysis determined thatananchorboxdesignwouldstillhavecaused interference intheopticalpath.Alsobeingabletoattainthestiffness required intheanchor boxwould prevent theuseofaluminum whichwasthematerial usedfortheopticalbench.Thismismatch inmaterial wouldhavecaused complications inmating toprevent anythermal distortions fromaffecting the instrument. Weight reduction became lessofadrivingfactorastimeprogressed. Thisreduced emphasis onweightreduction allowed forthepossibility strengthening oftheopticalbenchtobealoadbearing structure. Itwasdecided through theuseoffiniteelement analysis thatincreasing thedensity ofsupport ribsaswellastheskinthickness nearthegimbalmountarea(Figure 12)wouldbesatisfactory forHITS tosurvive launch. Mounting thegimbaltotheopticalbenchalsoservedtosimplify thedesignbyreducing thenumber ofparts.Italsosimplified instrument assembly andintegration sincethedevelopment ofthe opticalbenchassembly wasdecoupled fromthedevelopment ofthegimbalassembly andbothcouldbe thenconnected ordisconnected whenrequired withminimal effort. NASA/C P--2002-211506 224
Figure12.Optical BenchStrengthening forGimbal Mounting Gimbal Ca.qin.q Mechanism Affecting thedesign oftheHITSgimbal structure wasthegimbal caging mechanism. TheGCMwas needed forseveral reasons. Theadditional loadpathswerecreated through theGCMallowed thegimbal tobescaleddowninsize.Inaddition, thebending moment created bythedistance between thecenterof massandrotation axis,aswellastheestimated forcevectors, prevented thecaging mechanism from beingpartofthegimbalsupport structure asisnormally doneinamorebalanced gimbalassembly. The cagingsystem wasmounted totheinstrument baseplatesothattheCMwhensuperimposed onthebase platewouldbeinthecenterofatriangle formed bythegimbalsupports onthebasesideandthecaging mechanism atthevertex. Thecaging mechanism showninFigure13wasaparaffin actuated locking T-Bardesign withmanual resetmadebyStarsys Inc.Modifications toanalready existing designwereundertaken toaccount forthe higher preload. These modifications involved changing theBellville preload washers aswellas developing acustom tooltoallowtheT-bartobeextended forreset.Evenwiththehigherpreload the paraffin actuator stilloperated witharelease forcemargin of300%.Duetothelocation ofthecaging mechanism, resetting wasdoneinasemi-blind fashion requiring thetooltobeapplied whiletheoptical benchwasmovedintoplace. Figure13.HITSGimbal Caging Mechanism NASA/C P--2002-211506 225