Design, Development, AndTesting ofUmbilical System Mechanisms fortheX-33Advanced Technology Demonstrator AlanC.Littlefield" andGregory S.Melton" Abstract TheX-33Advanced Technology Demonstrator isanun-piloted, vertical take-off, horizontal landing spacecraft. Thepurpose oftheX-33program istodemonstrate technologies thatwilldramatically lower thecostofaccesstospace.Therocket-powered X-33willreachanaltitude ofupto100kmandspeeds between Mach13and15.Fifteenflighttestsareplanned, beginning in2000.Someofthekey technologies demonstrated willbethelinearaerospike engine, improved thermal protection systems, composite fueltanksandreduced operational timelines. TheX-33vehicleumbilical connections provide monitoring, power,cooling, purge,andfuelingcapability duringhorizontal processing andvertical launch operations. Two"rise-off" umbilicals fortheX-33havebeendeveloped, tested,andinstalled. TheX-33 umbilical systems mechanisms incorporate several uniquedesignfeatures tosimplify horizontal operations andprovide reliable disconnect duringlaunch. Introduction Thetwoground-to-flight umbilical connections fortheX-33vehicle arelocated facingaftoneithersideof thelinearaerospike engines (Figure 1).Thefuelumbilical provides thirteen connections tothevehicle, including liquidhydrogen supplyandbleedlines,aswellashigh-pressure gases(upto21MPa), environmental control, hazardous gassampling, electrical power,anddata.Theoxidizer umbilical provides seventeen connections tothevehicle, including liquidoxygen supply, high-pressure gases, environmental control, hazardous gassampling, avionics cooling, electrical power,anddata.The umbilicals areconnected afterthevehicle ismatedtotherotating launchmountinthehorizontal configuration andremainconnected through rotation tovertical, tanking, andlaunch. Theaftmounting of theumbilicals resultsina"rise-off" typeofdisconnect thatquickly subjects thegroundhalfofthe connection totheengineexhaust plume. Traditional vehicleconfigurations (withminimal aftarea)have favored side-mount umbilical configurations, whichcomplicate thedisconnect butprovide additional time toprotecttheground system fromdamage. TheX-33umbilicals arethelargestrise-offumbilicals developed foranyU.S.spacesystem. Umbilical System Requirements Therequirements fortheX-33umbilicals weredrivenbythegeneral vehicleconfiguration anddesign, as wellasspecific safetyandoperational requirements. Theaft-mounted umbilical "rise-off" configuration andfastacceleration oftheX-33offofthepad(0.9g)resulted inanavailable operating timeof1.4 seconds fromfirstmotionofthevehicle untiltheengineexhaust plumeimpinges ontheground umbilical. Theumbilical mustbedisconnected andstoredwithinaprotective enclosure beforetheplumereaches anysensitive components. Operational timelines allotted onlyonehourtoaccomplish theentiremating operation. Thisresulted inarequirement forsemi-automatic connection andleakcheckcapability. The quickturnaround requirement forsuccessive launches (24hours)leaveslittletimeavailable for refurbishment ofground systems. Misalignment ofthevehicleonthelaunchmount,dynamic deflections ofthestructure, anddriftofthevehicleduringliftoffrequired accommodating relative motions between the ground andflightcomponents ofupto4cm.Earlyinthedesign, thecustomer imposed several additional requirements onthesystem. Inordertoreducecostsandrefurbishment time,nopyrotechnic devices *NASAKennedy SpaceCenter, Florida Proceedings ofthe34thAerospace Mechanisms Symposium, Goddard SpaceFlightCenter,May10-12,2000 343