IssuesandConcerns (Lessons Learned) Fragility oftheSMAPinpuller (Failure #1):Onthequalification mechanism (integrated tothequalification instrument), anelectrical engineer inadvertently reversed twoconnectors andthenturnedthesystem on. Thisresulted inalotofcurrent beingapplied tothepinpuller fortoolongatime.Thepinpuller's Nitinol wiressignificantly surpassed theirtransition temperature foraconsiderable time,rendering thepinpuller inoperable. Themechanism hadbeendelivered withnoconnector (i.e.,withwirepigtails). Dueto extremely tightmassrequirements, theprojectelected todropalittlemassbyremoving themechanism's connector. Thecabling engineer, atthesystem level,usedtwoidentical connectors ofthesamegenderin thesamearea.Thiscreated theconfusion thatledtothemistake. Thankfully, theunithadalready gone through thenecessary system-level testsneeded toprovethedesignwasrobust. Lesson learned: Resist therequest ofaprojecttoremove yourconnector, andworkwiththecabling engineer toensure thatyour connector isdifferent fromthoseinthesurrounding area.Truthfully, we(themechanical team)werenot surehowtoprevent suchelectrical-team-induced failures fromoccurring. However, TiNihassince recommended thatwecouldhaveincorporated amicroswitch thatwouldshutoffpowertothepinpuller, eliminating thepossibility oftheSMAwireoverheating (andre-annealing). Fragility oftheSMAPinpuller (Failure #2):Aftertheflightmechanism hadbeenmechanically integrated intotheoptical benchoftheinstrument, alongperiodoftimehadtranspired beforethecabling was integrated toitsflightconnector. Duetothepauper-like funding forthisinstrument, various integrations occurred atspread-out intervals. ThismadeQuality Assurance (QA)coverage difficult, andduetothe financial situation QAwasreduced toabareminimum. Eventually, thewiringfortheflightunitwasbeing connected totheappropriate connector. Asthecabling engineer wasabouttosoldertheconnector in place,hechecked theresistance ofthepinpuller's primary andredundant circuits. Ontheprimary circuit, henoted2.4ohms,ontheredundant sidehefoundanopencircuit.Themechanism hadpreviously gone through adiminished flightacceptance testwithsuccess, andtheredundant circuithadpassed. The mechanism wasremoved, thepinpuller wasreplaced, andthemechanism returned toflightintegration. Analysis ofthefailedpinpuller foundthatawireonthepinpuller's redundant circuithadbrokenatasolder jointinternal tothepinpuller. Several designflawswerefound.(Although thepinpuller hadbeenbuiltat TiNiAerospace, thedesignwasaJPLdesignthatTiNihelpedbringintoproduction.) First,therewasno strainreliefforthisconnection. Second, therewasnoconformal coating usedtoinsulate thewiring.Third, agrommet thatwasoriginally inthedesign hadbeenremoved. Fourth, thewireusedwasfairlystiff. Lesson learned: Runyourelectrical connections byanexperienced packaging engineer, evenfordevices builtoutofhouse, andgettheirapproval ofthedesign before allowing itsuse.Thispinpuller is undergoing reworkatTiNiperourdirection. Strainreliefhasbeenaddedtothewiringandconformal coat hasbeenaddedtothearea.Agrommet isbeingaddedtothepinpuller housing. Finally, thewirewillbe changed toonethatislessstiff(samegage,butmorestrands). Fragility oftheSMAPinpuller (Failure #3):Thisincident isstillunderinvestigation, butthespeculation is thatafloating ground mayhaveledtoafailureoftheFPGAinternal totheMIROelectronics. Thisfailure resulted incurrent beingapplied tothepinpuller forlongerthanintended (seefailure#1).Assuming that thisisthecauseoftheanomaly, we'reunsure astowhatamechanisms engineer coulddotosafeguard his/herdesignfromafailureoftheelectrical system. Because thepinpuller requires between 120and150 milliseconds toactivate, anelectrical fusewouldnotbeanappropriate solution. Amicroswitch, as referred toinfailure#1,should alwaysbeincorporated intheSMApinpuller designtoprotectfromsuch failures. Position Sensing oftheMirror(notafailure): Therequirements forthismechanism dictatethattheremust beawaytoprovide feedback totheMIROcomputer thatindicates whenamirrorisatappropriate reflective positions. Reflective objectinfrared sensors werechosen toperform thistask.Thesideofthe mirrorwaspolished toprovide highreflectance. Duringcharacterization ofthemechanism, wefaceda dilemma. Duringassembly onecansetthesensitivity ofthesensors bychanging theresistance valuesof aresistor inserieswiththeinfrared transmitter. (Changing theresistor toalowerresistance resultsin increased current flowthrough thetransmitter, andmorelightistransmitted). Characterization provedthat atdifferent lightconditions, andatdifferent temperatures, thesensitivity changed somemore.Therefore atcoldtemperatures somesensors couldnotfindthemirrorwhentheyshould have,andathot 183