./ Milstar SolarArrayBoomDeployment Thomas B.Pace"andSteven M.Honodel* Abstract TheMilstarSolarArrayBoomisamature designthathasbeensuccessfully deployed intestdozens of timesandhasbeensuccessfully deployed onorbitsixtimes.OnJune7,2000,oneoftheBooms didnot fullydeployduringitsthermal vacuum ground testatcoldtemperatures. Theproblem wascaused bya pieceofground testequipment, arestraint mechanism thathaddeveloped excessive friction. This restraint mechanism hadbeenusedforover100testdeployments andhadneverbeenrefurbished. The anomaly hadapositive effectinthatthisrestraint mechanism wasreexamined todetermine wheredesign improvements couldbemadetoincrease friction margins. Asignificant lesson learned isthateven relatively lowcycledeployment testequipment canexperience wear-out problems andmustberoutinely inspected duringlongmultiyear programs likeMilstar. Introduction TherearetwoBooms oneachMilstarsatellite. EachpairofBooms servesthreebasicpurposes. First, theymovethetwosolararraysawayfromthevehiclesothatthearrayscanbesafelydeployed. Second, theyrotatethetwosolararrayssothatthearrayscantracktheSun.Andthird,theytransfer thepower generated bythetwosolararraystothevehicle. TheMilstarSolarArrayBoomisalargeelectro-mechanical devicethatisapproximately 23cm(9in)wide by23cm(9in)thickby171cm(67.5in)longandweighs about32kg(70Ib).TheBoomhastwohinges onit,aninboard hingeandanoutboard hinge(Figure 1).Eachhingecontains twosetsofnegator leaf springs thatprovide 32N-m(286in-lb)oftorque. Oneeddycurrent damper oneachhingeprovides damping. Theinboard hingeconnects theBoomtothevehicle andupondeployment, itrotates theBoom awayfromthevehicle. Theoutboard hingesupports aflexible substrate solararray(FSSA) andupon deployment, itrotatestheFSSAawayfromthevehicleandpositions itfordeployment. Therangethatthe inboard hingedeploys inthefirstpartofthedeployment iscritical. Iftheinboard hingedeploys toofartoo fast,thereisthepossibility thattheFSSADeployment Canister couldbedrivenintothevehicle payload (Figures 2&3).Therefore, adevicecalledaTripwire Mechanism (TM)isusedtorestrain themotionof theinboard hingeduringthefirstpartofthedeployment. TheTMconsists ofaspring-loaded spoolthatpaysoutastainless steelcable(Figure 4).Wheninstalled, theTMisboltedtoafixedpointonthevehicle. Thenitscableispulledoffofitsspoolandboltedinto another fixedpoint140cm(55in)away.Midway acrossthespanofthecable,thecableisplacedona hookthatismounted tothebaseoftheFSSA.Thesprings intheTMensure thatthecableisunder tension across thisspan.Uponbeingreleased fromitsstowed position, theinboard hingewantstofully deploybutitisrestrained bythetripwire cable.Although theinboard hingeisrestrained, theoutboard hingeisfreetorotate.Infact,thetripwire forceaidsthedeployment oftheoutboard hinge.Thisallowsthe FSSAtorotateclearofthevehicle payload andthuseliminates anypossible interference. Asthe outboard hingerotatestheFSSA,thehookalsorotates asitismounted totheFSSA.Aftertheoutboard hingerotates farenough, theangleofthehookchanges enough sothatthecableisabletoslideoffof thehook.Atthispoint,theinboard hingeisfreetorotateandcomplete thedeployment (Figure 5). Lockheed MartinSpaceSystems Company, Missiles andSpaceOperations, Sunnyvale, CA Proceedings ofthe35thAerospace Mechanisms Symposium, AmesResearch Center,May9-11,2001 237