Vertical testingoftheumbilical verified properleaktightness andlaunchdisconnect dynamics. The umbilicals werematedandtranslated toaworstcasemisalignment fordisconnect. Liquidnitrogen and liquidhydrogen (hydrogen umbilical only)werecirculated through theappropriate connectors tosimulate vehicle tanking. Liquidnitrogen wasusedinstead ofliquidoxygen toreducethehazardwhiletestingata temperature slightlylowerthanrequired. Leaktestswereperformed inthecryogenic condition. Finally, thecryogens weredrained andalaunchsimulation wasperformed byraisingtheflightpanelatthe launchacceleration rate.Allleakswerewithinspecification. Minorfrostdeveloped inseveral areasof thepanelsbutwasnotsignificant. Eachpanelwasdisconnected fourtimes,onetestforeachumbilical involved disabling thelockexpansion pintoforceasecondary disconnect. Alltestsweresuccessful. Thequick-release locksworked extremely well.Allfourlockstypically disconnected within5msofeach other.Lanyard loadswereasexpected. Primary release dynamic loadsweretypically around 1.8kN. Thesecondary release worked smoothly without damaging anycomponents. Thelanyard dynamic load forsecondary release was16kN.Thecompliance mechanism smoothly centered anddecelerated the ground panelandhoses. Thesystemwasunder-damped (asexpected) butthisdidnotaffectoperation inanyway.Totaloperation timefortheumbilical waslessthan1.1seconds withallfourlatches operating. Thetranslating framelatches released between 70and150msafterfirstmotion, depending onthevehicle starting position. Testdataindicated thatthefailureofatranslating framelatchwould delayoperation anadditional 50ms.Thefailureofalatchwasnotsimulated duringtest.Figure14 showsanoverallviewofanumbilical duringvertical testing. Figure15showsaclose-up viewofthe groundandflightpanelsmatedforavertical test. Conclusions andLessons Learned Although theentireprogram wentrelatively smoothly, therewereseveral lessons learned thatmayprove usefultoothers. Themostsignificant problem encountered duringtheprogram involved asimplepurge seallocated around theperimeter ofthegroundpanel.Thesealcompression forcewaserroneously assumed tobeminimal duetothesoftmaterial beingused.Theproblem occurred because, although the sealwassoft,itslengthwasnearly6m.Thesealwasactually capable ofgenerating several hundred newtons ofseparation forceandpreventing theplatesfromfullymatingundercertaincontingency conditions. Lubricating thesealallowed ittocompress adequately formating. Another problem encountered wasthat,duetotheshortschedule, theeffectsoflatedesignchanges werenotthoroughly analyzed. Aguidetrackfortheflightdoorwasaddedattheendofthedesign. Thistrackwaslocated too closetoaquick-release lockandactually impacted thelockslidingsleeveduringdisconnect. No hardware changes weremadeastheimpactoccurred fromaworstcasedisconnect position anddamage wasminimal. Leakage fromoneofthesealsontheretractlatcheswasnotedduringoneofthetests. Afteraboutaminute, theleakstopped. Thepistonsealwasapparently notseating properly when suddenly pressurized withnitrogen at17MPa.Thelatched stillreleased properly, evenwiththeleak. Thecylinder wascycledseveral times,andtheproblem neverrecurred. Asdiscussed previously, the frictioninadynamic fluidsealcanvaryconsiderably withpressure. Testing mayberequired todetermine theactualsealfrictionunderpressure. Thefinallessonlearned involved theteststand.Itisimperative thattheengineers understand the possible failuremodesofthetestequipment andhowtheymightimpactthetestorthetesthardware. Therealsoneedstobegoodcommunication between thetesttechnicians andtheengineering team. Priortooneofthetests,atechnician noticed asmallleakonthehydraulic system forthelift-offsimulator. Hesimplytightened aloosefittinganddidnotinformthetestteam.Toward theendofthenextcryogenic test,astheliftoffsimulator wasbeingpressurized fordisconnect, theairthathadentered thesystem through theleakyfittingslowlycompressed andallowed theumbilical toriseslightlyandinitiated an inadvertent disconnect. Thedataacquisition systems werenotyetoperating andalltestdatawerelost. Inconclusion, theX-33umbilicals weresuccessfully testedandhavebeeninstalled onthevehicle andat thelaunchsite.Theumbilicals utilizeseveral newmechanisms tosignificantly reduceoperational timelines. 357