PlanarTruss Thedeployable structure usedindeployment testingwasdesigned andfabricated basedonthedeployable trussstructure ofthemodular meshantenna developed byNTT[9].Theplanartrusswasselected toavoid uncertainties inanalysis models. Figure2showstheplanartruss.Theplanartrussiscomposed oftworib structures onbothsidesofthecenterbeam.Ribstructure consists oftheupperbeam,thediagonal beam, thelowerbeam,thesidebeamandtwosynchronous beams. Eachbeamisjoinedbyarotation hinge.The rightandleftdiagonal beamsandlowerbeams arelinkedbyaplate.Theplanartrussisdeployed and stowed bymoving plate(A)alongthecenterbeam.Teflonformsthefrictionsurface ofplate(A)todecrease frictionagainst thecenterbeam.Twoconstant forcesprings andamotoraremounted onplate(A).The constant forcesprings provide thedeployment forcetomovetheplanartruss.Totalspringforceis8.2N. Theplanartrussstowswhenthemotorwindsinthedrivecable,anddeploys whenthedrivecableis released. Whenplate(A)rises0.135m alongthecenterbeam,theplanartrussisfullystowed. Thebeams andplatesaremadeofaluminum. Thediameter ofthebeamis0.01manditsthickness is0.001m.The lengthoftheplanartrussis1.2m(deployed) and0.1m(stowed). Itsweightis4.7kg.Oneofourintentions istoexamine theeffectofthetension inthemeshcablethatconnects theupper-face ofbothsidebeams. Therefore, aloadcell(weight -0.090kg)andmeshcablewereattached totheplanartruss.Inthispaper, however, wedescribe inthecaseinwhichthetension ofthemeshcablewas0N. Deployment Testing Weperformed twokindsofdeployment tests.Onewasperformed undermicrogravityenvironment, the otherwasperformed ontheground. Weassumed thedeployment characteristics measured undermicro gravityenvironment represented thetruedeployment characteristics oftheplanartruss. Microgravitydeployment testinq Deployment testingundermicrogravityenvironment wasperformed inthejet-airplane. Figure3showsthe deployment testingsetupinajet-plane. Thetestingtimewassetto20seconds, whichwasdecided by considering theduration ofthemicrogravity environment. Theplanartrussdidnotstowcompletely, however, theplanartrusscanstowtotheconfiguration showninFigure3withinthegiventestingtime.We measured thetension ofthedrivecablethatwaswoundinorreleased bythemotor,andthedisplacement ofplate(A)fromthebottom. Thedeployment driveforcecanbecalculated byaddingthetensions ofthe drivecableindeployment andstowing motionanddividing by2ateachposition. Thefrictioniscancelled in thisprocess because ofcoulomb friction. Thedisplacement ofplate(A)indicates thedeployment position. Themeasurements duringdeployment andstowing wereperformed threetimesundereachcondition. Ground deployment testinq Figure4showsthedeployment testingsetupontheground. Theduration ofthegroundtestsequaled that ofthemicrogravitytests.Thesuspension system wasapplied tooffsetthegravityforcebecause thistest configuration canbeeasilyevaluated byavailable analysis tools.Inthesuspension system, thelowerside ofthecenterbeamwasfixedtothefloorandtheupperpartsofthesidebeamsweresupported bythe suspension cable.Theplanartrussdeployed inthegravitydirection. Theheightofthesuspension position is1.6mfromtheplanartrussasshowninFigure4.Twosuspension cablesweretensioned bythecounter weights through pulleys. Theweights were0.220kg(W1)and0.130kg(W2)respectively. Theweighton theleftsidewaslargerthanthatofrightsidebecause theloadcellwasinstalled ontheleftside.We attached weights tothestandsonbothsidebeamstoincrease theDIVoftheplanartruss.Whenaddingthe weighttothestandsshowninFigure2,thecounter weights (W1,W2)werecorrespondingly increased. We testedtheplanartrusswithlargeDIV.DIVcanbealteredbychanging theweightofthestands. Tominimize theweightneeded toincrease DIV,thespringforcewaschanged. Therelations among theDIVofthe planartruss,theweight, andthespringforceareshowninTable1.Astheplanartrussstows,thegravity torquechanges. Therefore DIVchanges withthedeployment position. Table1presents themaximum values. NASA/CP--2002-211506 354