Testing Adedicated qualification unitwasbuilttoperform developmental andqualification testing forthe retraction mechanism. Thedevelopmental testprogram iscomplete. Thequalification testprogram will takeplaceduringthespringandsummer of2001.Thefollowing paragraphs describe thetestingthathas already beenperformed, andthefuturetestingplanned forthemechanism. ProofPressure Beforefunctional testingcouldbegin,aproofpressure testofthetrunnion retraction mechanism to1.5 timesthemaximum design pressure (MDP)wasrequired bytheJSCsafetyorganization. Theproof pressure testwouldalsoserveasafunctional testsincethemechanism wasexpected toretractata pressure lowerthantheproofpressure. Theinitialproofpressure testrevealed somedefects inthe mechanism. Themechanism waspressurized to4.14MPa(600psi).Thepistonwasheardtounlock, but thetrunnion pindidnotretract. Thepressure wasthenreduced toasafelevelof517kPa(75psi).The trunnion pinwasshaken byhandanditretracted. Anaudible leakwasobserved buttheleakratewasnot measured. Apost-test examination ofthemechanism drawings andtolerances showed thattheleakwas likelyoccurring around thethreelockpins.Thelockpinsweresubsequently modified toaddano-ring grooveando-ring. Anewproofpressure testwasconducted aftertheadditional o-ringwasaddedtothethreelockpins.This testwasalsousedasafunctional evaluation. Themechanism wasagainpressured to4.14MPa(600 psi).Onceagainthepistonwasheardtounlock. Thetrunnion pinappeared tomoveasmallamount butit didnotretract. Thistimetherewasnoaudible leak.Thepressure wasincreased tothe5.17MPa(750 psi)proofpressure andheldforfiveminutes. Afterfiveminutes, leakage hadreduced thepressure by 345kPa(50psi).Thepressure wasthenreduced to4.14MPa(600psi).Thetrunnion pinwasshaken anditimmediately retracted. Amechanical jamwasnowsuspected. Afterthetest,thepinwasdisassembled. Smallnickswereobserved onthetipsofthethreelockpinsand ontheinsideofthemainhousing. Asubsequent examination ofthedrawings andtolerances showed that itwasindeedpossible forthetipofthelockpinstocatchtheedgeofthelockpinreceptacle holeonthe housing ifthelockpinreceptacles wereimproperly adjusted. Thisexplained whythetrunnion pinmoved asmallamount andthenstopped. Theproblem wassolved byproper adjustment ofthelockpin receptacles. Thepinwasre-assembled, thistimetightening thereceptacles untiltheycameincontact withthetrunnion pin.Thereceptacles werethenunscrewed justenough tobreakcontact. Afterthisfixthe mechanism retracted successfully. Mostlikelythisadjustment problem, andnottheleak,wasthereason whythemechanism didnotworkintheoriginal pressure test. Function Afunctional evaluation ofthetrunnion pinmechanism wasperformed withaninitialpressure of345kPa (50psi).Thepressure wasthenraisedto4.14MPa(600psi)inincrements of345kPa(50psi).Ateach pressure thepinunlocked andretracted asdesigned. Athighpressures thebumper cameoutofits groove duetothehighimpact energy. Adesignfixisinworktokeepthebumper initsgroove. After completion ofthisseriesoftestsitwasconcluded thatthenewadjustment ofthelockpinreceptacles was correct. Theprocedure wasdocumented inthemechanism riggingandrepairmanual. Calibration Adjusting thepre-load inthethreespringplungers adjusts themechanism operating pressure. Atestwas conducted tocalibrate thethreespringplungers. Withthemechanism intheextended andlocked position, thethreespringplungers wereadjusted tohavethesamepre-load. Pressure wasslowly increased untilthemechanism unlocked andretracted. Thispressure wasrecorded. Themechanism was thendisassembled sothatthespringplungers couldeachbescrewed inone-half turn.Afterre-assembly, pressure wasagainslowlyincreased untilthepinunlocked andretracted. Thisprocedure wasrepeated to determine themechanism operating pressure asafunction ofspringplunger position. Thesametestwas conducted usingquickburstsofpressure withsimilarresults. 55