Wefinallyreturnedtotheflexureideaanddecidedtoinvestigateatorsionflexuredesign.Theconceptis elegantinthattherestoringtorqueandtheaxialposition ofthemirrorcanbeobtained inonecomponent. Inaddition, thereissomeheritage forthistorsionflexuredesignintheScanning MirrorforInfrared Sensors 7developed byLockheed Missiles andSpaceCompany. Packaging thetorsionflexurerequired ahollowshaftandsizingtheflexureforstress/strain andrestoring torquewassimplyamatterofa parametric tradestudy.Theaxialpreload ofthetorsionflexurewasestablished basedonpredictions for launchloadsandaxialforcesexpected withintheactuator. Launch loadswerepredicted using conventional finiteelement analysis. Internal actuator forcesweredetermined usingaboundary element magnetic analysis program calledAmperes. Theaxialloadwasfinalized byinvestigating combined torsional andaxialstressintheBeCuflexureandconfirming thatsufficient margincouldbeobtained. Internal Actuator Forces Axialpreload intheflexureisneeded forseveral reasons, nottheleastofwhichistomaintain rotor position underinternal forceswithintheactuator. Theinitialdesignhadanominal gapof4.52E-04 (0.007 in)between therotorandeachofthestators. Therotorisinanunstable position between thestatorsand ispulledinthedirection oftheportionofthemagnetic circuitthatisclosest. Therefore, thereareboth axialandradialforcesontheshaftwithintheactuator. Theseforcesgrowby1.751E05 Nlm(1000Ib/in) ofmisalignment. Weknewthattheposition oftherotorsbetween thestatorswouldhavetobeprecise butwedidnotfullyappreciate theproblem untilwefirsttestedtheprototype. Initially, radialandaxialmotions oftheshaftundertheseforceswereaccommodated byabushing inserted intotheclearance holeinthebaseoftheactuator cavities intheshutterhousing. Theinsideof thebushing wasatoroidtolimitfrictionradially. Axially, ithadabearing surface thattheshafthubcould contact iftheaxialforcesduringoperation orlaunchbecame toogreat.Thisbushing wasAluminum 6061-T651 andplatedwithTeflon-impregnated anodize tolimitfriction. Theproblems wediscovered with thisdesignweretwofold. First,therewasverylittle"wheelbase"asthesebushings werebothnearthehuboftheshaft.Wecould notlimittheoff-axis forcesenough toprevent theshaftfromtiltingandtherotorsfromclamping against thestators. Thesecond problem wasthat,tolimittheaxialmotion, theaxialclearance between the bushing bearing surface andtheshafthubhadtobesosmallthatassembly became difficult. Infact, undertheinitialtestingwediscovered thattheaxialforcesweregreatenough tocausetheshafthubto clampagainst thebushing seizingtherotation. Wefirsttriedtocorrect theproblem byincreasing theaxialtension intheflexure. Ultimately, wewere abletomaketheactuator work,butnotbeforeweencountered another problem. Theinitialdesignofthe shutter housing didnothavethestructural member between thetwoactuator cavities. Therefore, aswe continued toincrease tension intheflexure, thehousing actually deformed andthegapsbetween the bushings andtheshafthubclosed. Weneeded toincrease tension ontheflexuretomaintain position of therotorsandintheprocess, weweredeforming thehousing andcausing alignment problems. To correctthisproblem, weaddedastructural member thatlaterbecame partofthehousing design. We werethenabletoincrease theflexuretension enough thattheactuator worked. Toreducetheradialmotion, wechanged ourbearing concept fromaradialbushing capturing theshaft nearthecenterofmasstoextending theshaftandaddingaprecision bushing thatwouldrideonthe innerdiameter oftheendcaps.Ultimately, thisadded"wheelbase"andattention toconcentricity sufficiently limitedthetiltoftheshaft.Whileexamining theaxialforcesandmotionoftheshaft,we determined thatthetolerances usedtodetermine theactuator gapwereinsufficient. Therefore, we precisely measured eachofthecomponents thatimpacted theaxialposition ofthestatorsandrotors. A rigorous CTEanalysis oftheshutterdesigntosimulate thechanges tothecomponents at2Kwas developed 8.Thespreadsheets havebeenusedforeachoftheshutterunitsdeveloped todateandcan quickly bemodified forspecific partdimensions. 8