Thesquarecross-sectioned endpieceattachedtotheflexureintheshaftisdesignedtoprotrudethrough theendcapwhereitengagesacomponent withasquarehole,theSpringPreloadRing.Thiscomponent isdesignedtoberotateduntilthepropertorsionalpreloadisimpartedtotheflexure.Thispreloadis necessarytoreturnthemirrortotheopenpositionwhenpowertotheactuatorsisterminated. Inaddition, thispreloadhelpstoensurethatthemirrordoesnotflapuncontrollably duringlaunch.Thepreloadrings areset,clampedinplaceduringpreliminary assembly,andpinnedtotheendcapduringfinalassembly. Toanchortheflexureaxiallytotheendcaps,asteelnutisrunontothreadsintheflexureendpieces. Thethreadsextendthroughthesquareholeinthepreloadringallowingthenuttoeffectivelyanchorthe flexuretotheendcap/preload ringstack.Thenutononesideisrunontothethreadscompletelytothe preloadringwhilethenutontheothersideisrundownontoastackofwavesprings.Inadditionto affixingtheflexuretotheendcaps,thesenutsallowaxialadjustment toensurethattherotorsattachedto theshaftareintheproperlocationforoptimalperformance oftheactuators.Thespringsunderoneof thenutsprovideaxialpreloadfortheflexureandmaintainadesiredpreloadasthestructuralcomponents shrinkgoingcold.SincetheCTEoftheBeryl!iumCopperflexureis25%lessthanthatoftheAluminum ofthestructurefromroomtemperature to4K_,thepreloadandtherotorpositionwouldbelostwithout thesprings.Thispreloadisnecessarytomaintaintherotorpositionduringoperationandlaunch. Ahardstopfurtherlimitstheloadstransferredtotheflexureduringlaunch.Thiscomponent isAluminum 7075platedwithTeflon-impregnated Anodizeforlubricity.Itprovidesarotarystopforthemirrorinthe openposition.Inaddition,ithastwouprightsthatstraddlethemirrorarmthroughout itsentirerangeof travel.Theseuprightsarepositionedsuchthatthereisa0.2-mm(0.008-in)gapbetweeneachupright andthemirrorarm.Thisgapissufficienttoallowfreedomofmovementfortheshaftbuttorestrictaxial motionintheeventthatlaunchloadsexcitethesuspended massoftheshaftcomponents. Restricting theaxialmotionisnecessary toprevent stressintheflexurefromviolating material strength limitsand ensurethattherotorsdonotimpactagainst thestatorsintheactuators. Finally, aretaining deviceismatedtotheendcaptocapture thestackofringsattheflexureinterface. Thegapbetween thetopofthestainless steelnutandtheunderside oftheretainer islessthan0.127mm (0.005in).Thisgapensures thatintheeventofabreakage inonehalfoftheflexurewiththemirrorin theclosedposition, theaxialmotionoftheshaftintheopposite direction willbelessthanthegap between themirrorarmandthehardstopuprights. Therefore therestoring torqueoftheremaining half oftheflexurewillbeenough toopentheshutterwithout frictiononthehardstop. Sensory Components Therearethreesensory components ontheshutter: 2Cernox resistance thermometers andavariable reluctance position sensor. TheCernox thermometers arecalibrated tooperate fromroom-temperature (300K)downtopumped liquidHeliumtemperature (1.4K).Oneofthesesensors islocated oneachof theendcaps.Theywiltbeusedtomonitor temperature onorbitandtoverifypowerdissipation during component leveltesting. Avariable reluctance rotaryposition sensorwasdeveloped tomonitor theposition ofthemirror. The sensorisanelectromagnet intheshapeofa"C."Therearetwoelectromagnetic coilswiredinseries, oneoneithersideoftheopening. Eachcoilhasgreater than300turnsof99.99% pure38AWG,HAPTZ insulated copperwire.Thebobbins forthecoilsarepartofthemagnetic circuitandaremadeofHiperco 50Aheat-treated tooptimize performance. Toresolve position, amagnetically conductive rampispassed through thegapinthesensor. Asthisramppasses between thepoles,thechange inthickness ofthe material changes theairgapofthecircuit. Thischange ingapchanges thereluctance ofthecircuit. The reluctance change ismeasured bypassing anACsignalthrough thecoilsandmeasuring thechange in inductance ofthecircuit. Therampiscurved, bonded tothecounterweight, andsizedtobeataminimum thickness whentheshutterisopenandatamaximum thickness whenitisclosed. Therawresponse of thesensorisapproximately 1.5Vacrossthefullrange.Thisresponse isthenscaledto1.25to3.75V fromopentoclosedposition, respectively. Sincetherampiscontinuous, itcanprovide continuous position dataforallintermediate positions oftheshutter mirror,aswell.