abovethedoortomeasuremovementofthedoorasdrynitrogenwasallowedbackintothecamera body.Thedoorslowlyroseoffthesealretainerastheinternalpressurewasequalizedtotheambient pressureinthecleanroom.TheO-ringwasstillcompliantandrelaxedastheexternalpressurewas removedfromthedoor.Coldweldingand/orgallingwasthenruledoutsincetheO-ringhadenough springforcetopushthedoorawayfromthesealretainerandcloseinspectionrevealednosignsofcold welding.ThisalsowouldhavebeenthecasewhentheTRWthermalvacuumchamberwasinitially evacuatedsincethepressuredifferentialacrossthedoorwouldbeenreducedinasimilarmanner. Withthedifferentialpressureequalized,thedoorcouldbeopenedandrunningtorqueandsealadhesion couldbemeasured. Usingatorquewrenchtodrivethedooropen,thesealadhesionplusrunningtorque wasmeasuredtobe2.6N-m(23in-lb)whichwasneartheexpectedvalue.Sealadhesionshadnever beenmeasuredabove2.3N-m(20in-lb)andwitharunningtorqueofaround0.5Nm(4in-lbs),theseal adhesionwas2.2N-m(19in-lb).ThefullcapabilityoftheSTARSYSactuatorasmeasuredin subsequent testing,wasaround10.2N-m(90in-lb)whichgaveafactorofsafetyofover4abovewhat wasmeasured. Withrunningtorquewithinnormalspecifications, noproblemswerefoundwiththe mechanism. Furtherdisassembly andinspections showedalldimensions forbushingsandother components tobewithinspecifications atroomtemperature. Nobindingorinterference wasfoundwhich couldhavecontributed tothefailure.AdditionaltestingontheTorlon®bushingsshowedthatthe coefficientofthermalexpansionwasasexpectedandthatanalytically therewerenoconcernswiththe mechanism bindingatlowtemperatures. Theover-center torqueonthedoormechanism wasalsofoundtobewithinspecifications atabout1.9Nm(17in4b).Sincethisflightmechanism wassetupinanover-center condition,duetonormalrotational andmachiningtolerances, therewasconcernthatiftheover-center torquewastoohighthenitcould havecombinedwithanotherfailuremodetoresultinexcessiveretardingtorque.Thiswasshownnotto bethecasewithtestingonotherengineering unitsevenforanincompressible O-ring.Conservatively, theflightunitwasre-assembled withthemechanism adjustedinaslightlyunder-center conditionby buildinganewadapterbracket. STARSYS Actuator Inspection andTest(FaulttreeItemsBandC) FailureoftheSTARSYS rotaryactuator wasoneofthefailuremodesidentified onthefaulttree.X-ray inspection oftheunitdidnotshowanyanomaly. Aswasexpected, theopenactuator sheardiskhad ruptured duetoexcessive pressures insidetheactuator. Theopenactuator outputshaftwasslightly extended whichexplained whythelatchandlimitswitches werenotengaged. Somedriveshaftrotation wasalsoobserved intheX-raysoftheactuator. Therewasnoevidence ofanyforeign material ordebris thatcouldhavejammed themechanism. Theopenactuator cartridge wasthenremoved fromthe actuator assembly. Astheactuator wasremoved, thelatches andlimitswitches fellintoplace. The slightlyextended outputshaft,whichwasfrozenintheparaffin, hadprevented theactuator fromre-setting completely. Thesheardisklookedlikeanormally ruptured diskwithnosignsofanymaterial weakness. Material properties weremeasured forthesheardiskandwereasexpected. Therewerenosignsofwax leakage andinternal inspections ofthewaxcartridge werenominal. Forcemeasurements weremadeto determine therunning torquefortherotarymechanism andwerenominal atbothroomtemperature and at-45°C. Priortototaldisassembly, thecloseactuator cartridge wasremoved andinstalled ontotheopenactuator sideoftherotarymechanism assembly. AtSTARSYS, theunitwastestedtofailurewithafullstallto characterize theperformance oftheactuator andsheardiskundertheseconditions. Thisfullstalltest, performed at-45°C,simulated thecondition wherethedoormechanism didnotrotateandallbushings andlinkages werefrozensolid.Thetemperature profiles weresimilartothosewhichweremeasured at thetimeofthefailureupuntiltheactuator reached atemperature ofaround 129°C,atwhichtimethe sheardiskruptured. Thisisslightly lowerthantheestimated failuretemperature of132°CatTRW,but wouldbeexpected withthismoreseveretestcondition. Thedoormechanism linkages andtorsionshaft wouldhaveallowed morerotation oftherotaryactuator andthusahighertemperature atsheardisk rupture. Itisinteresting tonotethatbothsheardiskswerenearlyprotected sincethePSMCshut-off temperature wassetat133-135°C. Thepeaktorqueatsheardiskfunction was10.4N-m(92in-lb)vs. 23