Intricacies ofUsingKevlar CordandThermal Knives inaDeployable Release System: Issues andSolutions Alphonso C.Stewart* andJasonH.Hair* Abstract Theutilization ofKevlarcordandthermal knivesinadeployable release system produces anumber of issuesthatmustbeaddressed inthedesignofthesystem. Thispaperproposes designconsiderations thatminimize themajorissues, thermal knifefailure, Kevlarcordrelaxation, andthemeasurement ofthe cordtension. Design practices canminimize thepotential forthermal knifelaminate andelement damage thatresultinfailureoftheknife.Aprocess forin-situinspection oftheknifewithresistance, ratherthan continuity, checks and10xzoomoptical imaging candetect damaged knives. Testsallowthe characterization ofthebehavior oftheparticular Kevlarcordinuseandthedevelopment ofspecific prestretching techniques andinitialtension values needed tomeetrequirements. Anewmethod can accurately measure thetension oftheKevlarcordusingaguitartuner,because moreconventional methods donotapplytoarimidcordssuchasKevlar. Introduction TheMicrowave Anisotropy Probe(MAP)Spacecraft utilized anovelSolarArrayRestraint andRelease System (SARRS) design thatfeatured aKevlarcordandthermal knivesastheprimary solarpanel restraint andrelease components. The7.6-m(300-in) Kevlarcordencircled thespacecraft tosecurethe solarpanelsintheirstowed configuration forlaunch. Onceinorbit,oneoftworedundantly configured thermal knivessevered theKevlarcordandpermitted thepanelstodeploy. Anumber ofissuesaroseduringtheSARRS development involving thethermal knives, Kevlarcord behavior, andthemeasurement ofthetension intheKevlarcord.Theissuesencountered andtheir solutions willbediscussed, including aprocess forexamining thethermal kniw_saftereachuse,a procedure forcharacterizing theKevlar cordbehavior indifferent environments, andamethod for measuring thetension inthecordusingaguitartuner.Thesolutions arepresented inageneral manner suchthattheinformation canbeapplied tootherconfigurations ofKevlarcordandthermal knives. The discussion ispreceded byabriefintroduction oftheMAPSpacecraft andtheSARRS Configuration. SARRS andMAPSpacecraft Configuration Thepurpose oftheMAPmission istoperform afullskyscanofthecosmic microwave background in ordertostudytheoriginoftheUniverse. MAPwasdesigned, fabricated, andtestedatNASA's Goddard SpaceFlightCenteraspartoftheMedium ClassExplorers program. MAPwaslaunched intolowearth orbitbyaDeltaII7425-10 launchvehicle fromtheEastern RangeonJune30,2001.Afterseparation fromthelaunchvehicle, thesolararraysandsunshieldweredeployed andthespacecraft continued on toorbitabouttheL2Lagrange point. Spacecraft Confi.quration TheMAPspacecraft usesapassively cooled microwave differencing assembly tomeasure thefullsky cosmic background atatemperature of2.7K.Sincethemicrowave instrument mustbekeptverycold, thesolararrayshavebeenconfigured toformpartofthesunshield thatwillalways shadetheinstrument fromthesun.Themicrowave instrument ismounted ontopofahexagonal spacecraft busandthe protective solararrayandsunshieldcombination ismounted tothebottomofthebus,asshowninFigure 1. NASAGoddard SpaceFlightCenter, Greenbelt, MD Proceedings ofthe36thAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/CP--2002-211506 243