-Commandzerocurrentthenwait1second -Sendacommandable "kickcurrent",+2.5mA,(Waitacommandable time,3seconds) -Commandzerocurrentthenwait1second -Readthesensorandstorethevalue -Openshutterrelayandturnoffthesensor _.F,ghtColdTestingSideAPull-inandH01dResultsThissoftwareversionwasimplemented andthe._1_T:r_.r: [!T:r!r: electronics wereinstrumented on6/14/01.The2_="0.5[:"'--__-----::-------::::::[i!:iiiilli_---:::::::::::::::::::::::::::::::::::::::::::::::::i iii!iwaveforms verifiedproperoperationandthefailure_oneverrepeated.Othertestswererunontheflight_, instrument including reversepolarityclosings, _,-o_ unexpected lossofpower,andattemptingtouseSideB_-1_-80 -60 -40 -20 0 20 40 60 80 torelease theshutter afterbeingdeliberately stuck _"_- FlighPU_lol_ ?ur_en_ _i_ea_ I_Vlu_l_suar%l_l_r_,_)sult s closedusingSideA.Thereverse polarity testsshowed &1,....... pull-inandholdcurrent comparable tothenominal _Iiii!i!i20.2........_........i........_........i........i.....!-_---i.... operations• Thisverified thatthemagnetic circuitfully__Iiiiii_! 0....... '_........ ' ---'*........ saturates regardless ofpolarity whenthehigh,60mA, _I_?Likepolarityreleases Ii pull-incurrent isapplied. Sideaalways released during _°_t,-_-i:_'':' [::i..i' asudden lossofpower, butSideAcouldbemadeto_,-1/I I I I I I I -_-80 -60 -40 -20 0 20 40 60 80 • ozstayclosed undercertain conditions Unfortunately, Pult-ln Current ateachMeasurement (mA) SideBoperations wereunsuccessful inreleasing the shutter onceSideAwasstuckduetoresidual magnetism. Thisultimately became theaconcern ofFigure7.Release current dataforthe SIRTF management andprompted thestudyinto IRACflightshutter mitigation approaches whichcouldbeimplemented on theflightsystem. GSFCActuator Testing andAnalysis Considerable effortwentintotestingthe2spareunitsatGSFCtoduplicate thefailureexperienced onthe flightunit.Theimpacts ofsoftware andelectronics boardperformance wereeliminated asrootcauses of thefailurethrough extensive characterization. Inorderforthemechanism toremain closedwithzero currentthefollowing equation mustbesatisfied: TRestoring Spring -<TResiduat Magnetism 4-TFriction Boththemagnetic andfrictional sources oftorqueinthemechanism whichcouldcausethemechanism to stickwithzerocurrent whereinvestigated atlengthatbothroomandcryogenic temperatures. The actuator components werealsotestedseparately tocharacterize therelease currents andtorque generated inanactuator without theinfluence ofbeinginthemorecomplicated shutter assembly. This section ofthepaperwillsummarize thetestinghistory, magnetic analysis efforts,andsomeofthekeytest resultsobtained atGSFC. Theresultsoftheseeffortsconfirm thattheflightfailureisduetointimate contact between rotorandstatortabsurfaces andthetorquegenerated byresidual magnetism. History Ourinitialsuspicions werethattheproblem wasrelatedtoresidual magnetism intherotarysolenoid. The theoretical possibility thatenough residual magnetism couldbedeveloped intheactuator toovercome the restoring torqueofthespring,andthusnotallowforfailsafe operation, wasanaspectofthedesignand wasanticipated fromthebeginning ofthedesign process. Theelectronics weredesigned toallowfor reverse polarity currents tobeapplied totheactuator tocancelanyresidual magnetism andthepotential needforadegauss command wasidentified. Theproblem duringinitialtesting priortodelivery tothe IRACinstrument wasthatwedidnotobserve azerocurrent stickcondition onanyofthe4units developed atGSFCincluding theflightunit.However, wedidseelowerthandesired holdcurrents onthe flightunitduringinitialassembly andtesting. Anon-magnetic shimwasplacedinthemagnetic circuitto maintain afixedgapinthecircuitintheclosed condition. Atthetime,itwasthought thatthisshim provided enough coercive forceonthemagnetic circuittoeffectively reducetheresidual magnetism inthe actuator components afterthe60mApull-incurrent wasapplied. Afterreassembly withthisshim,desired release currents wereachieved. Unfortunately, aftertheflightfailureoccurred, acloserlookintothe NASA/CP--2002-211506 19