Relationship Between theDifficulty IndexandtheEvaluation Accuracy of Ground Deployment Testing Hironori Ishikawa andAkiraMeguro* Abstract Anindexthatwellreflects thedifficulty ofground deployment testing istheratioofgravity torqueto deployment torque. Theobjectofthisstudyistoquantitatively clarifytherelationship between thisindex andtheevaluation accuracy ofground deployment testing. Weperformed grounddeployment testsusinga simpleplanartrussinmicrogravityandgravityenvironments. Ground testsinwhichtheindexvalueofthe planartrussisincreased arealsoperformed. Acomparison ofexperimental andanalysis resultsyieldsan empirical equation thatsetsalinearrelationship between thedifficulty indexvalueandtheevaluation error ofthegroundtesting. Weconclude thatthemodular approach allowslargespaceantennas tobedesigned thatcanbewellassessed bygroundtesting. Introduction Largedeployable spacestructures suchassolarpaddles, deployable antennas and,,sunshields havebeen developed forfuturesatellites. Theyaredesigned tohavesufficient deployment reliability afterlaunch environment andshapestability against thermal andvibration disturbances. Deployment reliability isthe mostimportant factorinavoiding thefailureofmissions. Therefore, deployable spacestructures shouldbe evaluated byground deployment testing beforelaunchtoconfirm theirdeployment reliability. Whenwe perform ground deployment testing, gravitycompensation equipment suchassuspension systems and support systems shouldbeusedtoavoidexcessive gravitytorqueandforce.Ingeneral, wecannotexpect gravitycompensation equipment towellsupport themoving parts;onereason isthatitisimpossible to createareallyaccurate forceandtorqueprofile.Asaresult,deployment behavior inground deployment testingisnotthesameasin-orbitmotion, soananalysis modelmustbeusedtoevaluate theinfluence of thegravity compensation equipment onthedeployment characteristics. Thegravity forceandtorque increase asthespacestructure becomes larger.Thismakes itverydifficult toevaluate theactual characteristics ofthedeployable structure. Inthesecases,weareactually evaluating thecharacteristics of theground testingequipment, instead ofevaluating thecharacteristics ofthedeployable structure. Itshouldbepossible topredicttheaccuracy ofdeployment testingforadeployable structure ofgivensize. First,wepropose thedifficulty indexvalue(DIV)todefinethedifficulty ofground deployment testing. The indexistheratioofgravitytorquetodeployment torque. Figure1indicates DIVcalculated byMitsugi's formulation [1]forlaunched andplanned spacedeployable structures [2]-[6].Here,drepresents thestowed diameter. Next,wequantitatively evaluate thedifficulty indexandtheaccuracy withwhichthedeployment characteristics canbeestimated fromground testing. Finally,weintroduce anindexthatindicates thesize limitofdeployable structures thatstillpermits accurate ground testevaluations. Inapastpaper[7],we clarified therelationship between DIV(1-100)andtheevaluation errorofthegroundtesting, andobtained anempirical equation thatsetalinearrelationship between DIVandevaluation errorofthegroundtesting. However, theDIVofmostrecentlargespacestructures exceeds 100sothereliability oftheempirical equation isnotvalidforthesestructures. Therefore, weextendtheempirical equation tocoverDIVsover 100.Thispaperdescribes therelationship between DIVandtheevaluation erroroftheground testingfor DIVsofuptoapproximately 1000.Werevisetheempirical equation andconsider theevaluation accuracy of ground testsusingtheexample ofthemodular meshantenna developed byNTT[8]-[10]. *NTTNetwork Innovation Laboratories, NTTCorporation, Kanagawa, Japan Proceedings ofthe36thAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/C P--2002-211506 353