Failure Recovery Testing Individual Hinge-line Toraue Tests Individual hingelinesweretestedonanearbyhigh-precision granitetablewithinaweekjusttoshow thosecomponents wereworking properly andwouldn't needtobereworked. Itwasquitefortunate that otherdeployment testingwasongoing onanother program andwasbeingperformed inthesame building. Thegranitetableusedforthosetestsprovided asuitably fiatlocation tobegintherecovery testing. Morecorrective actions ontheRRSandthedeployment MGSEwereimplemented whilethe spacecraft andarrayweredispatched forsystem-level environmental testinginnearbyfacilities. R_straint CablePreload Withtheremoval ofthecutcables, itwaspossible toexamine themclosely. Whenthecablefittingswere compared totheirdrawings, someimportant dimensional discrepancies werediscovered. Thelengthof thecableshadbeenunwittingly increased! Thediscrepancies hadbeenoverlooked duringtheincoming inspection andsourceinspections atthevendor. (Thestatistical sampling approach inplaceatthetime didnotuncover thepartproblem.) Thecarefully determined torques applied totherestraining nutwere invalidated withthelengthenedcables, whichhadaii0wed thetensioning nuttobottomOutandinducea counter-twist inthecable,reducing theestimated preload byanunknown amount. Withtheproper functioning oftheRRSdirectly dependent onthepreload, thiswasaveryserious problem indeed. Itwasdecided thatitwouldbebettertorelyonloadwashers fordetermining thepreload inthecables, so thisdesignchange wasimmediately implemented. Simultaneously, athorough analysis wascompleted byLMSSC tomakesurethatthenewcableconfiguration wouldn't loseitspreload duetoflightvibrations andcup-cone settling. Theloadwashers werechecked several timesovertheremaining months before launch, andtheyshowed theexpected minorrelaxation overthattimewhichwasentirely tolerable. Just beforethefinalCloseout ofthelaunchvehiclefairingltheloadwashers werereadforthelasttime, confirming thatfullpreload wasstillintactforallsixcables. Theelectrical leadswerethenclipped off, leaving theloadwashers inplaceforflight. ShockAbsorber Redesiqn Theextensive investigation following theApril1998deployment failureconcluded thatthetwoprimary causesforthefailurewere: 1.Inadequate cablerelease movement duetolowcablepreload andexcessive shockabsorber friction, and 2.Firingthecornerredundant cablecutters priortofiringallsixprimary cutters andallowing the solararraytodeployandcomplete theextraction ofthesuccessfully cutcables. Atfirst,itwasthought thatthecounter-twist induced inthecableswasaprimary causefortheexcessive splaying ofthecableends,andtbat thesplay,ngwasacondition forjamming. Benchtestingwas undertaken totestthistheory_- C-a-b-les withanormally cutendWerepositioned inthepathofasecond cutter,whichwhenfiredstillentrapped thepre-cutcable.Theconclusion wasobvious: splaying froma normalcutlikewhatwouldbeseenon-orbit wasenough tointerfere withthecablecuttingofthe redundant cable.Therefore, totrulyretainredundancy, aftercommanding theprimary cutter,eachcable mustbecutandfullyextracted, ornotcutatall.Tobecutandonlypartially extracted wasneverseenin anyproperly configured tests,sothisredundancy-threatening failuremodewaslabeled "non-credible". Thefollowing designmodifications wereimplemented asaresultofthefollow-up investigation: 1.Decrease thefrictiondragforcebetween thecablefittingandthesplitwasher, usingaseriesof benchtestspriortoinstallation ofhardware onthespacecraft. 2.Increase thestrainenergystoredinthecablesbyincreasing theflightpreload. 3.Change thefiringsequence tofireallprimary cuttersfirstinthreepairs,followed muchlaterbyan automatic firingoftheredundant cuttersifneeded orabortbycommand. 4.Change thecutterinstallation procedure togetbetteralignment ofthecableinthecutters. 220