mirrortoquicklyrotatetotheclosedposition.Thespeedofthismotionmakesanglemeasurement difficultinthisregime. Severalcurrentinputlevelswererepeatedtoverifytherepeatability ofthemirrorpositionwithcurrent. Theopenandclosedpositionsofthemirrorwererepeatabletolessthan30arcsec.However,wefound thatifcurrentissteppeduptoaparticularlevel,theangleachievedbythemirrorisslightlylessthanifthe currentlevelisinputasastepfunctionfromzero.Thedifferenceinanglerangesfrom0.05to2.2 degreesdependingonlocationwithintherangeofmotion.Therewerenotenoughdatapointstakento achieveastatisticalsampling.However,itseemsapparentthattheinternaloff-axisforcesinthe actuatorsarebeingtransferredtothebushingsontheshaftintheformofstaticfrictioninthese intermediate positions.Sincethecoefficientofkineticfrictionisalwayslowerthanthecoefficientofstatic friction,theforcefightingtherotationofthebushingswillbelowerforamovingbushingthanforastatic bushingunderthesameload.Inaddition,therotationalmomentum oftheshaftaccelerating toagreater angularvelocityunderastepimpulseratherthanaslowincreasemayovercomemoreofthisfrictionand completeagreateranglepriortostopping.Dataiscurrentlybeingreviewedtoquantifyfrictionalforces. Testinghasalsoquantifiedexcesstorqueasafunctionofcurrentandmirrorangle(Figures10and11). Thetestwasperformedatroomtemperature andmeasuredtheminimumexcesstorqueinthemotorto be14.15mN-m(2.004in-oz)witha60mAinput.Finally,thefailurebehavioroftheshutterwastestedon thesecondflightspare.Theabilityfortheshuttertoopenitselfifaflexurebreakageoccurredwas verified;however,thisabilityishighlydependentonthegapbetweentheflexurenutandtheretaineron theendcap.Ifthegapistoolarge,themirrorarmwillbearonthehardstopuprightandthesubsequent frictionbetweenthetwopartswillpreventtheshutterfromopening.Ifthereisnocontactbetweenthese parts,halfoftheflexureisstilladequatetoopentheshuttermirror.Withnoaxialforceontheflexure(i.e. abrokenflexure),theshutterisdesignednottoclose.Thisbehaviorwasalsoconfirmedbythistest. Finally,theshutterhassurvivedaqualification levelvibrationtestandapost-vibelifetestispending. Problems andSolutions Duringthedevelopment ofthismechanism, several problems wereencountered thatrequired solutions. Thissection identifies themajorproblems andtherationale behindthesolutions. Suspension System Duringtheinitialconcept ofthismechanism, wewrestled withhowwecouldachieve 38degrees of rotation mostefficiently andrepeatably atcryogenic temperatures. Wewanted toavoidballbearings because ofthedifficulties involved withsizingthebearings warmtoachieve theproperfitcoldandwith lubrication atliquidHeliumtemperatures. Inaddition, ourmotionwasnotgoingtobecontinuous andwe wereconcerned aboutdegradation ofperformance overtimeduetodisplacement ofbearing lubricant. A flexureseemed logical, butwhatshoulditlooklike? Weinitiallythought offlexpivotsbutfoundthatthemostrotation wecouldgetoutofonewasontheorder of15degrees. Thiswouldmeanthatwewouldhavetogang3ofthesepivotstogether toachieve our38 degrees. Ourconcern withdoingthiswaslosingourcenterofrotation duringoperation andmaintaining structural rigiditytosurvive launchloads. Wethenthought ofusingashaftpointed oneachendthatengaged ajewelled cup.Wethought this configuration wouldbearelatively low-friction interface thatwouldmaintain itscenterandstillallowfull rotation. Aclockspringwouldprovide ourrestoring force.Thisconcept seemed soundbutwebecame concerned aboutthewearofthejewelled cupafterlaunchandthroughout thelifeofthemission. In addition, thecupswouldhavetobeaxiallypreloaded tomaintain contact asthemechanism wentcold. Thispreload wouldalsohavetobesufficient tomaintain theposition ofthecupduringlaunch. The designquicklybecame morecomplicated thanweanticipated andwasabandoned. 7