ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Description ofthemechanism Inordertoachieve very-high resolution overalongstrokeinonlyonestage,themoving partofthe proposed mechanism ismagnetically suspended; duringoperation thereisnocontact between themoving andstaticparts.Thesystem isdivided intothreesubsystems: (i)theguiding system, basedon3magnetic bearings constraining thein-plane movements (Tx,Ty,Rz)oftherotor,(ii)thepositioning/steering system, usingvoice-coil actuators andhigh-resolution linearscales, whichdrivestheusefulDOFs(Tz,Rx,Ry)and (iii)alocking device. Themechanism isshown inFigures 1to3.Therequired spacetooperate the mechanism isacylinder of¢=320mm andh=80mm. Themechanical interface consists of3holes ((!)=6mm) evenlyspaced ona290-mm-diameter circle.Mostofthemechanical partsaremadeofAI-7075. Themagnetic partsaremadeofVACOFLUX thathasgoodperformance atcryogenic temperatures. All thecontact surfaces ofthelocking devicehavebeenhardanodized andtreated withPTFEtoimprove theirtribology properties. Figure1.MABE3DOFhigh-precision mechanism Magnetic bearinqs Unlikevoice-coil electromagnetic actuators, reluctance forceactuators orelectro-magnets allowlarge displacements inthedirections perpendicular totheactionoftheactuator andhence,aregoodcandidates formagnetic bearing applications [3].However, inthesereluctance forceactuators, theforcecomesfrom thevariation oftheenergystoredinthemagnetic circuit,whichisproportional tothesquareofthecurrent inthecoilsandinversely proportional tothesquareoftheair-gap thickness. Thisquadratic relation ofthe forcetotheapplied current leadstotheneedforoperating theactuator aroundabiascurrent (i=io+ic). This biascurrent isthesource ofmostofthepowerdissipation instandard magnetic bearings. Forthis application, permanent magnets havebeenusedtocreatetherequired biasmagnetic field,hence drastically reducing therequired electrical power.Thepermanent magnets aremadeofSamarium Cobalt (SmCo5). Morepowerful magnets canbemadeofNeFeBo buttheliterature hasreported thatthismaterial experiences instabilities atcryogenic temperature [4,5,6].Themagnetic circuitismadeofVACOFLUX, whichhasalsoproven tobeefficient atcryogenic temperature. Therelation oftheforcetotheair-gap thickness leadstoanegative stiffness, resulting inanunstable open-loop system thatrequires acontrol system tooperate it.Thetwoquadratic relations alsoleadtolargenon-linear effects thatcanbe minimized byapropermagnetic design[7].Theselected magnetic configuration isshownonFigure4. NASA/CP--2002-211506 198
Figure2.MABEStator Figure3.MABERotor Theguiding controlarchitecture isbasedonthreeindependent magnetic bearings, eachconsisting of(i)a reluctance forceactuator, (ii)ahigh-resolution eddy-current position sensor and(iii)alocalcontroller. BeingsimplePID,thelocalcontrollers havebeenimplemented usinganalogelectronic components. The bearings areplacedtangentially toacircleandseparated by120°(Figure 2).Thediameter ofthecircleis twicetheradiusofgyration ofthemoving payload, leading tothesameopen-loop frequencies forthe constrained translation androtation DOFs.Thebearings areoperated neartheirmagnetic equilibrium pointleading topowerdissipation inthebearings lessthan1mWovertheentirethermal operating range (-10°C/+50°C). Figure4.Heteropolar reluctance forceactuator Steering Thethreesteering DOFs(1translation Tzand2rotations Rx&Ry)aredrivenbymeans oflinearvoicecoils.Forthesamereasons asmentioned previously, onlytheactuators basedonSmComagnets have beenconsidered. Thetranslation androtation displacements aremeasured bymeans ofthreelinear measurements. Thehigh-stroke toresolution ratio(>22bits)imposes theuseofdigitalmeasurement devices, eitherlaserinterferometers oropticallinearscales. Because theproposed mechanism willinduecoursebeusedinaclosed-loop system drivenbyaspecific opticalsensor(e.g.awavefronterror),theemphasis wasputontheresolution oftheactuator ratherthan onitsprecision oraccuracy. Linearscaleshavebeenpreferred tolaserinterferometer because oftheir rugged design, goodrepeatability, andveryhigh-resolution (1bit=0.3nm).Thealignment procedures havealsobeensimplified byusinganopticallinearscalewithalargestandoff (3mm). NASA/C P--2002-211506 199
Thesteeringcontrollawisbasedonamulti-input/multi-output (MIMO)frequency-shaped LQG.Because ofthecomplexity ofMIMOcontrollers, thecontrolsystemhasbeenimplemented onanADSP-21020 processorfromAnalogDevice,forwhichacompatible space-qualified processorhasbeendevelopedby TEMICunderanESAcontract.TheDSPprocessorisalsousedforthemonitoring ofthemagnetic bearingsthrough16-bitAIDconverters. Lockinq device Duringthelaunchandlanding periods, allthemobilepayload movements shouldberestrained; therefore alocking devicehasbeendesigned. Thecontact surfaces between thefixedandmobilepartsconsist of (i)acylindrical bumper madeofVlTON (seeFigure2),(ii)analuminum/aluminum conicalcontact, and(iii) threesinglepointcontacts. Inordertoimprove thetribology properties ofthesecontacts andtoensurea stiction-free release whilein-orbit, theVlTONbumper contains 10%ofPTFEinclusions andthealuminum contact surfaces havebeenhardened andtreated withPTFE,according to[8]. Currently thepreload forceisobtained bymeansofalocking screw;however, duringthePhaseC/Dofthe project, anautonomous locking mechanism willbedesigned. Itshouldbeabletorelease themechanism afterthelaunchandtolockitbackafterthein-orbit experiment hasbeenachieved. Itshouldalsobe lockedwhenthepowerisoff.Preliminary investigations haveledtotheselection ofaparaffin actuator to drivethismechanism. Tests Preliminary testshaveshownthatthemechanism experiences someControl Flexibility Interaction (CFI) forboththeanalogmagnetic bearings controllers andthedigitalsteering controller. Inbothcases,itisthe support plateofthebearings andthevoice-coils thatisdestabilized bythecontrolsystem. Toreducethis CFI,ithasbeendecided (i)toreducethecontrolbandwidth downto16Hzand(ii)tonotchthecontrollers. InthePhaseC/Doftheproject, themechanical designwillbechanged toincrease (i)themodalfrequency ofthisplate(currently 330Hz) and(ii)itsstructural damping. Functional andenvironmental testshavebeenperformed onthemechanisms. Thesetestsconsistof: •Performance testsverifying thatthemechanism iscompliant withtheperformance specification; •Vibration testsverifying thatthemechanism (excluding theelectronics) cansustain thevibration loads fromtheAmerican SpaceShuttle; •Thermal testsverifying thatthemechanism (excluding theelectronics) canoperate withintherequired thermal rangeandthattheextreme non-operational temperatures donotdamage themechanism. Oscilloscope ] t MABEMechanism Metrology SystemMultimeter MABE Electronicsf Commands  s,tio ,_[__q I c uis,tionII ZYGOVMEBox14GPrB nteFfaceJMETROLOGY PC Figure5.Testelectronics layout NASA/CP--2002-211506 200
Figure6.Testset-upwithgravity compensation device Performance tests Theperformance testsconsisted ofbothstaticteststodetermine themechanism resolution (noise) and stroke, anddynamic teststodetermine theclosed-loop bandwidth andthedynamic perturbation attenuation. Thetestsetupisrepresented inFigures 5and6.Itconsists ofthe3-DOF mechanism, a3axislaserinterferometer andagravitycompensation devicemadeofthreesoftsprings. Duringthetest, thesetupwassubjected toaground acceleration of80Pgrmsor10-l°m2/Hzbetween 0and500Hz. Figure 7showsthePSDoftheground acceleration. _-8...... i ................................... o.....   - iiiiii!  i.ii.!.i ;;iiiil,ii'___iI_-10 N _  ,-12............. -'...................', , _ , -13 ' ' ' 10-1 100 10_ 102 103 Frequency (Hz) Figure7.Ground acceleration PSDatMicromega facilities Duringthestatictests,thepistonandtiltofthemechanism wereacquired atasampling rateof2kHz,a moving average over0.75second isthenperformed andtheRMSvalueoftheaveraged datais computed. Themeasurements arerepeated atthevarious extreme positions. Thecontrolcurrents inthe bearing andthevoice-coils arealsomonitored; theseareusedtocompute thepowerdissipated inthe mechanism andalsotheperturbation forcegenerated bythemechanism onthesupport. Table1givesthe resultsofthesestatictests.Inaddition toverygoodpositioning/steering performances, verylowpower dissipation inthemechanism (bearings andvoice-coils) hasbeenobserved. Thisismainlyduetotheuse ofpermanent magnet-based actuators andtotheoperation ofthebearings around theirmagnetic equilibrium point.Furthermore, theperturbation generated bythemechanism canbeneglected. NASA/CP--2002-211506 201
Table1.Statictestsresults TEST TESTCRITERIA Results Magnetic bearing Resolution RMSvalueoftheMAover0.75s<1nmrms 0.774nmrms Powerdissipation Perturbation Steering DOF Resolution Piston Tip-tilt Stroke Piston Tip-tilt Powerdissipation<100mW/channel Quasi-static partofcontrolforcePSD<10-uN2/Hz RMSvalueoftheMAover0.75s<1nmrms RMSvalueoftheMAover0.75s<10nradrms +/-2.5mm +/-1.25mrad <100mW/channel0.06mW 0.8910-yN2/Hz 0.793nmrms 8.391nradrms +/-2.5mm +/-2.5mrad 0.025mW Theresponse ofthemechanism toadynamic position perturbation (i.e.,thermal load)hasbeen established bymeasuring theerrorofthesystem toapositioning/steering command. Aharmonic command wasapplied successively onthe3DOFatvarious frequencies, forvarious amplitudes (to identify potential non-linearities) andnearthemaximum strokeofthemechanism. Asthesystem has proventobeverylinear,onlytheresponse ofthesystem tothelargestperturbation willbeconsidered, in ordertoobtainthebestsignaltonoiseratio.Table2givestheexperimental resultsofthedynamic test. Figure8showstheexperimental frequency response forthepistonDOF,compared withtheprediction takingthegravitycompensation deviceintoaccount andtotheprediction ofthesystem in-orbitoperation. Onecanseethat, (i)Theattenuation factorof-100dBisobtained atafrequency of0.001Hz,whichistentimesbetter thantherequired 10.4Hz,despite thereduced bandwidth; (ii)Higherattenuation ratiosareachievable inazero-genvironment; (iii)Thecrosscoupling between theDOFonwhichthepositioning/steering command isapplied and theotherDOFcannotbeneglected. Itcanbeshownthattheobserved crosscoupling isduetothenon-uniformity ofthestiffness ofthegravity compensation springs. Thesestiffness variations havebeenmeasured andintroduced inthemodeland Figure9showsthecomparison between thepredictions, withandwithout thestiffness non-uniformity, and theexperiment. Thisconfirms thattheobserved crosscoupling isduetothegravitycompensation device and,therefore, betterperformances areexpected forthein-orbitmodel. = o = IO0Piston 0.........}.................... ---A.e.°.,o° ............... .................. .........................,_f--- //" // I-',/ I-- S,rlulati0n- Free "/ /[] E×perirr, ent200i 104 10.2 ]00 1L-I_ Frequency (Hz) Figure8.Pistonmovement attenuation factor NASA/C P--2002-211506 202
Vibration Tests Vibration tests,including sinusoidal identification andrandom qualification tests(Figure 10),havebeen performed onthemechanism. Theapplied random vibration levelsaretheonesapplicable forpayloads to beflownonboardtheSpaceShuttle GAScanister carrier. Special attention hasbeenpaidtothelocal vibration modesofthemobilepartinthestatorairgap(whichisonly0.3mm).Inordertoverifythatno contact occursduringthevibration testbetween movable partsandthehigh-resolution eddy-current, the signalofthelatterhasbeenmonitored duringthevibration tests.Thishasshownthat(i)thepeak deviation fromthesteady-state position is0.22mm,whichissafeenough; (ii)thereisarotational settling movement ofthepayload onitsbumper atthestartofthevibration testsequence. Thishasledtoreredesignofthelocking device. Frequency (Hz) 2O 2O-50 5O-600 600-2000 2000PSDLevel(g2/Hz) Qualification 0.025 +6dB/oct 0.15 -4.5dB/oct 0.025Acceptance 0.0125 +6dB/oct 0.075 -4.5dB/oct 0.0125 Overall 12.9grins 9.1grms1 "1- ,I•,=0.1 8....... !........................  .......:!i-!!!I................................... ! i 0.01.......................................................... 10 100 1000 10000 Frequency (Hz) Figure10.Vibration testlevels Thermal Tests Themostsensitive hardware istheopticalheadofthelinearscaleswhoseoperating andstorage thermal rangeare-10°C/+50°C and-40°C/+50°C, respectively. Therefore, thermal testshavebeenperformed on themechanism, withtheexception oftheelectronics, toverifythatisitabletofacethisthermal range. Figure11showsthetestsetup;themechanism hasbeenplacedinaTHERMOTRON thermal chamber andequipped withthermocouples atadequate locations (rotor,stator,gravity compensation device...). Duringtheoperational test,themechanism isswitched onandremains atrestatitsneutral position (Tz=Rx=Ry=0mm/mrad). Figure12showsthethermal cycleforthetestinoperating conditions. Theoutputofthemagnetic bearing sensors andthelinearscales, aswellasthecontrolcurrent flowing inthevarious actuators, aremeasured duringtheconstant temperature plateaus. Thesystem hasproventobefullyfunctional attheprescribed temperatures. Lowerresolution valueshavebeenobserved duringthesetests,mainlyduetothehighlevelofperturbations inthethermal chamber (vibrations fromthecoolerpumps, airblowing thesystem...). Figure13showsthevariations ofthecurrent inthebearings duringthetest.Thesevariations comefrom thethermal expansion oftheeddy-current sensor support. Because theclosed-loop keepsconstant the distance between theeddy-current sensorandthebearing rotor,thisresultsinabiasbetween thezeroof thesensorandthemagnetic equilibrium pointofthebearing, hencetheincreased current. Athermal cyclingtesthasalsobeenperformed onthelockedmechanism (8cyclesbetween -40°Cand +50°C). Nomechanical failurehasbeenreported. Onlyaslightsticking between themoving payload and thebumper hasbeenobserved, whichcanbeeasilyovercome bythevoice-coils. NASA/C P--2002-211506 204
Figure 11.Thermal testsetup c'°I/ /i ,__1Support#1 2-Support_ ............. 3-Locking 50 4-P,0tor .Y..-F;;...... '%. 5-s_,r,r I"/_ 3",k B-zerogdevice 'i"",X,?F 4o --_i?-:-- ...........i-.....::....!,....,.......!.......!................ /ii,,x"u'i!ii_i>,i,,,,iii ........................................_.._............i...........i............i............. £ ;/i,,'/ii"'_,?_!ii _i_. :// : : \;\ : : :;j':_ i/ ! i !_,\ i i ! _.20p-'--:_-_-_'_*............ ',....................... i.-"__,\......... ',....................... -=-_,_,-_-z_=-_ i ', i ','_,: ! ,_';;;_.......// I I°P-.......... i............ ', ....:.......... ;G\-....F...... i....... /,Y',....... i o_-...........!............i............f............i........,,._,-:.............,,,----,_,"......i......... 0 1 2 3 4 5 6 7 8 Time(heum) Figure12.Temperature measurements (operating tests) Conclusions Duringthisproject, a3-DOFs (1translation &2rotations) long-stroke, high-precision mechanism hasbeen developed. Themechanism canbeusedtocontrolopticalmirrors translational androtational motions for interferometric spacemissions, orforalignment /pointing /refocusing purposes onprimary segmented or secondary telescope mirrors. Itisbasedonthemagnetic bearing technology thatexperiences contact-free movements. Thisallowsachieving simultaneously largebandwidth, highresolution andlongstroke.The achieved performances ofthemechanism are1nmrm_over5mmforthetranslation DOF,and10nradrms over+/-2.5mradforthetworotation DOFs. NASA/CP--2002-211506 205
o7 , !  -MB#]] II.......... r,4B_I o_.......... _-...... ,.......... _.......,............. ,............ ".......,..... _'_..........il.........!i........i__!...........,i_!!l!li_"__i_!_._.........ii.......... inii,_..........:'.............._:'_i_'_",_i-,-iJ!_....._i,,_,i,_........,,,,!,;!........ I......................................... ........".............io_L.........,.................. i,#!_._L............i!............A o 6 Time(Hours) Figure13.Bearing power(operating tests) Thepowerdissipation inthemechanism hasbeenkeptverylowtoallowitsuseincryogenic applications. Thanks toaninnovative magnetic design, thepowerdissipation inthemechanism hasbeenproventobe lessthan1mWovertheentirethermal range. Themechanism hassuccessfully passed adedicated testcampaign, including random vibration exposure, functional testatextreme operational temperature, andthermal cycling. Aproto-flight modelofthe mechanism iscurrently beingdeveloped toundergo in-orbittestonboardaSpaceShuttle GASCanister carrier. Thisactivity hasbeenperformed undertheESAGSTPresearch andtechnology program. References 1.H.Takahashi, T.Akiba&F.Kondo, Amagnetically-suspended mirrordrivingmechanism forFTIR, FourthInt.Symposium onMagnetic bearings, August 1994,Zurich. 2.C.P.Britcher &N.J.Groom, Current andFutureDevelopment oftheAnnular Suspension andPointing System, FourthInt.Symposium onMagnetic bearings, August 1994,Zurich. 3."Active Magnetic Bearings", Gerhard Schweitzer, Hochschulverlag, 1994. 4.D.M.Cannon &M.Brereton, "Design ofmagnetic bearing foruseinSIRTF's Tertiary Mirror Assembly", SPIEVol.1340Cryogenic Optical Systems andInstruments IV,1990,pp.373-382. 5.K.H.MOileretal.,"TheDipinDemagnetization Curves ofSintered NdFeB Permanent Magnets", Acta Physica Polonica, vol.A72,pp.89-92,1987. 6.J.R.Costetal.,HighPerformance Permanent Magnet Material "Radiation effects inRare-Earth Permanent Magnets", pp.321-326, Materials Research Society, 1987. 7.C.K.Sortore etal.,"Permanent Magnet BiasedMagnetic Bearings-Design, Construction andTesting", 2n_International symposium onMagnetic Bearing, July12-14,1990,Tokio,Pg175-182. 8.SpaceTribology Handbook, European SpaceTribology Laboratory, 1997. NASA/C P--2002-211506 206
fieldcanbegeneratedthateitheropposesoraidsthemagneticfluxinthatcoilcircuit.Simultaneously changingthecurrentintheopposingcoilgeneratesatorqueintheplaneofthetwocoils.Theresulting torquetiltsthemirrorplatformaboutitscenter.Similaroperationoftheothertwocoilsproducesmotionon theorthogonal axis,sothatthemirrornormalcanbepositionedanywherewithinanopticalcone.The resultingmotionisduetothedifferentialforcesproducedinindividualcoils,andresistingspringforces. Themirrorplatformismountedonaflexibleberylliumcopperdiaphragm, whichprovidessupportand restoringtorqueinanydirectioninreactiontotheelectromagnetic torques. Inadditiontothetipandtiltmotionsproduceddifferentially, pistonmotionofthemirrormayalsobe generated. Currentinallfourcoilsmaybevariedsimultaneously, positioning theplatformlinearlyalong itscenterline,thusprovidingtheadditionaldegreeoffreedom.Thismotioncanbeutilizedinfocusing applications. OperationoftheFSMisfundamentally differentfromthatofotherdesignsusingvoice-coils. Torqueis producedbyvaryingthemagneticfieldsinsidetheattractiveairgaps,ratherthaninducingLorentzforces onmovingcoils.Thedesignisalsophysicallydifferentinthatitusessmallmagnetsandlargecoils,while thevoicecoildesignsuserelativelylargemagnetsandthincoils.Becauseofthis,theextranumberof turnsandlargerwiresizereducespowerconsumption, whilesmallmagnetsofferlowercostandeasier handling.Oneaddedfeatureisthestationarymountingofthecoils,resultinginhigherreliability,asano movingelectricalconnections arerequired.Nomechanical clearanceproblemsassociated withmoving partsinsideandaroundthecoilsarepresent,thusmakingthedesigneasiertoassembleandreducing manufacturing cost. TheFineSteeringMirrorassemblyismorelimitedinangularrangethanvoice-coiloperateddevices,due toasignificantandlimitingdecreaseinmagneticefficiencywithincreasingairgap.However,theFSMis significantly lesslimitedinthisregardthanisthepiezoelectric actuator.Piezoelectric actuatorsmay require100Voltstoachievedisplacements ontheorderof0.5degrees,whereastheFSMcanmove2.5 degreeswithonly15Voltsapplied.Driftandlinearity,majorconcernsinpiezoelectric actuators,arenonexistentwiththeFSM. Thefirstdevelopment unit,showninFigure1,usednon-contacting inductivepositionsensorsmounted betweenthecoilstoprovideclosed-loop feedbackcontrol.Theinductivesensorspresentedcross couplingeffectsduetothesensorsnotbeinginlinewithcoils.Thesesensorsarealsoexpensive. The inductivesensorswerereplacedbyopticalsensors,whicharerelativelysmallandcanbepositionedin linewiththecoils.Theyrequirecalibrationandsoftwaretocompensate fornon-lineareffectsinherentin thesesensors.Theirworkingrangeisintherangeof1to4.5mm. TheFSMhasonlyonemovingpart(themirrorplatform)mountedonafrictionless flexurespring; therefore,thepositionaccuracyisprimarilyafunctionofthesensorerror.Thermaldistortioneffectsofthe platformarefilteredoutbyusingtwosensorsperaxis.Thetwocoilsforeachaxisarephysicallywiredin series.Inthisway,theproblemofcontrollingfourchannelshasbeenreducedtoasimplematterof controlling twocoilpairs,eachforoneaxisof motion. _" Figure1.Prototype FineSteering Mirror NASA/C P--2002-211506 208
Analysis Magnetic designandanalysis oftheFSMwasperformed usingtheAnsoftMagnetFEprogram. Two-and three-dimensional finiteelement modelswerecreatedtocheckthemagnetic saturation. Thenetmagnetic fluxinthecircuit,whichisacombination ofthefluxduetothepermanent magnets andthecoilfluxes, determines theposition ofthemirrorplatform. Mirrorplatform motionisgenerated byincreasing theflux densityinoneairgapwhilesimultaneously decreasing itintheopposite airgap.Themagnetic modelwas usedtofindtheoptimum circuitconfiguration thatwouldallowfluxtobebothincreased anddecreased efficiently. Thechangeinairgapduetomirrorplatform tiltingdrastically affectsthefluxintheairgap,resulting in non-linear behavior whichisveryhardtocontrolandnotpowerefficient. Afterthefirstdevelopmental unit, themagnetic designwaschanged toonehavingarelatively constant airgap.Figure2depictsthe magnetic modeloftheimproved coil/pole-piece design. AsshownintheFigure,theairgapbetween the pole-piece andthebackiron remains constant for thefullrangeofmotion,thusexhibiting relatively linearmagnetic force(torque)behavior. Figure3showsthegenerated forceasafunction ofcoilcurrentandthetiltangle. Oneofthemostimportant reasons forclosinga position looparound theFSMistoreject disturbances causedbythetarget.Ifthemirroris tostayfocused onthetargetseveral kilometers away,eventhesmallest vibrations couldbe significant. Smallervibrations aregenerally highin frequency, whereas largeramplitude disturbances arelowerinfrequency. TheFSMwasdesigned toFigure2.Magnetic ModelofImproved design haveabandwidth of1Hzformotionof20,000micro-radians, abandwidth of10Hzformotionof2,000 micro-radians andaminimum of100Hzbandwidth formotionssmallerthan200micro-radians. Forcevscurrent andtilt (flatyoke,cylindrical housing design, NdFe48 3_90 tilt,deg-2 -1 0 1 210.10.5 current, amp Figure3.ForcevsCurrent vsTiltangle NASA/CP--2002-211506 209
Themoving partsoftheFSM,i.e.themirror,themirrorplatform, andtheflexurediaphragm weremodeled usingtheANSYS FiniteElement program toestablish thestructural resonant modes. TheFEmodelis showninFigure4.Results ofthemodalanalysis for1mmand1.5mmmirrormountthickness are summarized below: Structural Modes-Baseline Configuration 7.2Hertz-AxisofRotation Mode MirrorMountThickness -1mmThick 557Hertz Plunging Mode 1024Hertz TiltMode MirrorMountThickness -1.5mmthick 712Hertz Plunging Mode 1468Hertz TiltMode Inordertoincrease thespanbetween the operating frequency andthestructural resonance frequencies, themirrormount thickness of1.5mmwasselected. Figure4.FiniteElement Modelfordynamic analysis Lessons Learned Theprototype FineSteering Mirrorassembly, asshowninFigure1,wastestedextensively byMCOand JPL.Duringsoftware andalgorithm development, afrequency shiftwasobserved. Thefirstfundamental frequency dropped fromapproximately 150Hztoapproximately 80Hz.Careful inspection oftheFSM revealed thattheFlexure Diskdiaphragm hadasustained structural failure. Fatigue crackssurrounding thecenterpostofthediaphragm, asshowninFigure5,showsthestructural failure. Further investigation alsorevealed degradation ofmagnet polepiecesduetocontact andde-bonding ofthemagnets frompole pieces(Figures 6&7). Figure5.Fatigue crackaround centerpost Figure6.Debonding ofmagnet frompolepiece NASA/CP--2002-211506 210