Lessons Learned Duringthepostfailureinvestigation, several notable lessons inthedesign, fabrication, assembly and testingofaspaceflightmechanism werelearned. Errorsduringeachphaseoftheevolution ofaspace flightmechanism cangoundetected. Wearefortunate thatthischaracteristic oftheIRACshutter mechanism wasdiscovered duringground testing. Problems andsolutions thateluded detection during eachmajorphaseoftheIRACshutter mechanism development willnowbediscussed. Desiqn Designing adefined fixedgapintoaclosedmagnetic circuitisabasicconcept thatshouldhavebeen implemented ontheIRACshutter mechanism rotaryactuators. Infact,onaprevious mechanism, the DIRBE shutter (alsodesigned byGSFC), thiswasaccomplished bygoldplating ofthecontacting surfaces ofthemagnetic circuit.Weunderstood thattheoretically thedesignwassensitive tochanges in gapintheclosedposition. However, sincetestingofengineering unitsneverrevealed thissensitivity, this possibility waslargelyignored. Provisions weretakenintheelectronics tocounteract thisproblem should itoccur.However, theimplications ofdiscovering thisproblem laterintheprogram werenotfully appreciated duringtheearlydesignphase. Inaddition, material selection couldhaveminimized thepotential forthisproblem tooccur.Wechose Hiperco 50Abecause ofitsstableproperties fromroomtemperature to2Kandforitshighfluxsaturation levelswethought wewouldneed.Hiperco doeshavearelatively lowcoercive forcewhenheattreated properly. However, othermaterials, suchaspureiron,canexhibitanorderofmagnitude lowercoercive forceandalsohavestableproperties overourtemperature range. Fabrication Becareful whatyouaskfor;youmightgetit.Duringfabrication ofdevelopmental unitsitissometimes tempting tousepartswhichmayhavebeendiscrepant orhavebeenmadetotolerances thatwilllaterbe tightened fortheflightmechanism. Inthiscase,whereadesign issosensitive tosmallvariations this couldbeacritical errorinthinking. Theparameters established bytesting ofearlyprototypes often become abenchmark forthemechanism developed forflight.Therefore, tightening tolerances toimprove fitorfunction mayinvalidate previous qualification effortsandmovethedesigntoanunproven state. Assembly Duringtheassembly oftheflightunit,carewastakentoalignallofthecontact surfaces inboththeAand BSideactuators. TheASidewasaligned firstandtheBSidewasthenallowed toconform totheASide alignment. Measurements ofrelease currents weremadetoensurethedesired valueisobtained during theassembly process. Release currents ontheASidearetypically lowerthantheBSide.Justpriorto integration intotheIRACcoldassembly, theflightshutter mechanism wasdisassembled forcleaning. Uponreassembly, itunderwent acharacterization at4Kandwasthenintegrated intothecoldassembly. Notuntilafterthefailureoccurred wasitappreciated howmuchofanimpacttheassembly process could haveontherelease currents and,therefore, thereliability ofthemechanism. Itistheorized thatthefinal assembly oftheflightmechanism andsubtleshiftsduringoperations andvibrations caused theASide actuator tobecome marginally "sticky" anddetection ofitsbehavior eluded us.Therefore, itiscriticalto understand theimpactoftheassembly process ontheperformance ofaspaceflightmechanism. Testin.q Evenifextensive testdataindicates noproblem withamechanism, ifflawsexistinthetestprogram orifa designerrorisbeingmasked, theremaystillbeaproblem waiting tosurface. Inthiscase,continued system levelcharacterization oftheshutter mechanism waslimitedduetoconflicts withothersub-system demands suchassoftware checkout, opticalalignment, etc.Itisbelieved thatthefailuretoopenwithzero currentontheAsideactuator waspresent butnotdetected throughout system leveltestingatGSFC.The lessonlearned hereforamechanism engineer isnottoassume yourjobisdonewhenamechanism is delivered tothesystem level.Donotbowtoschedule concerns. Makesurethatthemechanism is functioning properly atthesystem level.Makesurethatthepropercheck-outs canbeimplemented atthe system level. NASA/CP--2002-211506 24