SolarArrayDesign Options Thetightvolume requirements incombination withtherequired on-orbit stiffness ledtosomevery constraining features. Therequired on-orbit stiffness canbeachieved in3ways: 1.Thickrigidpanels 2.Mastsupporting structure withblanket 3.Geometric stiffness withsemi-rigid panels Option 1wasdiscarded asitdidnotfitinthetightvolume constraints. Option 2couldnotmeetthe stowage volume requirements and/orthefrequency requirement. Although theblanket specific mass looksveryattractive, onemustrealize thatallsupporting structures anddeployment andrestraint mechanisms aretobeincluded togettheactualnumber forthespecific massatEOLcondition (i.e., W/kg). Furthermore, Fokker SpaceBVhadexperience withflexible blanket technology (Ref.:Olympus 2) toleadtorelative complex andcostlymechanisms withadisappointing specific power(<20W/kgat EOL).Hence, alsothisoptionwasdiscarded. Itbecame quiteclearthatanovelconcept wasrequired, allowing averycompact stowage method while stillproviding astiffbackbone inthefullydeployed configuration. Theideawastointroduce curvature in thedeployed configuration, bycurving thethinpanels byspecial tension wires.The"Curwin ¢''concept wasborn[1].Assuch,acomplicated mastcouldbeavoided, alsoallowing agoodsolarcellarea coverage asthefullpanelareacouldstillbeusedeffectively. Curwin©Overall Design Description The"Curwin "3concept isquitedifferent fromconventional solararrayconcepts inthewaythatituses geometric stiffness toreachhigherdeployed Eigenfrequencies instead ofaseparate backbone structure. Thefullydeployed wingsareslightly curved likeameasuring tape,theactualcurving occursafterthe wingshavebeendeployed. Notonlythedeployed bending stiffness isensured, alsothetorsional stiffness ofthearrayiscovered. Thetension wiresformakindofshearweb,whichclosestheopenCstructure, providing therequired on-orbit torsional stiffness. Notethatthepanelcurving hasnonoticeable detrimental effectonthepower,asthesolarincidence angle,i.e.,thecosineeffect,isnegligible. ForTeledesic, the"Curwin ©"solararrayconsists oftwowingsontopofthePrimary Deployment Mechanism (PDM)boom.Adoublesolararraydrivemechanism (SADM) linksthetwowingstotheboom, insuchawaythatthetwowingscanrotateaboutthesameaxis,sotheyalwaysstayinthesameplane together, perpendicular tothesun'srays.Between eachofthewingsandthisSADM, thereisastructure intheformofanopenCarbon FiberReinforced Plastic (CFRP) frame. Thissnubber frameislocated behindthefirstpanelandhouses theprimary curving system inaddition tothetensioning partsofthe primary andsecondary system. Duringlaunch, italsosupports theSADMandpartofthePDMboom. EverysolararraywingofTeledesic isidentical andhas14panelsof4.3mx0.50mtomeetthepower demand of4.3kWatEOL.ThethinpanelsaremadeofCFRPcarbonfiberfacesheetwithanaluminum honeycomb. Thepanelsandwich thickness is4mm.Inthestowed position, the14panelsarestacked withaspacing ofabout3mmeach.Thisleadstoatotalstackheightofabout100ram.Theinter-panel hingesatthelongedgesandanumber ofcupsandconesdistributed overthepanelsurface assurethis spacing. Through 6ofthesecupsorconesateachedgeoftheindividual wingpackage, anelement is running fromthehold-down bracket onthespacecraft tothesnubber framethatisontopofthepanel stack.Theothercupsandconesareheldundercompression bythissnubber frameononehandanda so-called snubber frameontheotherhand.Thissnubber frameismeanttoincrease thenumber of support pointsforthepanelstomeetthestowed resonance frequency requirements off_>35Hz. 2Olympus solararraywassuccessfully deployed inorbitin1987 3Curwinconcept andprinciple hasbeengranted apatent:No:US6,091,016.and EPNoEP0926068by G.J.A.N. Kester;FokkerSpaceBV 253