InflatableBoomControlled Deployment Mechanism forthe InflatableSunshield InSpace(ISIS)FlightExperiment George H.SapnaIII,JohnFolke,Charles R.Sandy, andDavidP.Cadogan Abstract ILCDover,Inc.hasdeveloped thewirebrakeControlled Deployment Mechanism (CDM)foruseinthe Inflatable Sunshield InSpace(ISIS)Shuttleflightexperiment. TheISISexperiment isa1/3-scale sunshietd demonstration unitprecursor totheNextGeneration SpaceTelescope (NGST). TheNGST sunshield isa35x15meterdiamond-shaped multi-membrane sunshield thatwillbeusedtopassively protectthetelescope fromthermal radiation andstraylight.TheISISrequirements callforasmooth and predictable deployment ofthesunshield byinflatable boomsthataregoverned bythewirebrakeCDM. Todeploythesunshield, inflation gasisintroduced intotheinflatable booms, whichgivesthemrigidity andcauses themtounrollfromthestowed position. Astheboomisinflated, thetorsional resistance of thewirebrakedevicecauses thepressure intheboomstoincrease untilthepointwhereitovercomes the torsional resistance ofthewirebrakeandtheboomunrolls. Thewirebrakeoperates byconverting mechanical energy toheatthrough theplasticdeformation ofaductilemetalwire.Associated mechanisms reactthetorquefromthewirebraketotheinflated portionoftheboom.Through useofthe CDM,theboommaintains aconstant internal pressure duringdeployment toprovide sufficient structural stiffness. Thewirebrakegoverns theinternal pressure ofthetubesuchthattheboomprovides the required forcetodeploythesunshade plusanycontingency load.Technical information detailing the development, design, analysis, andtestingoftheCDMaredescribed inthispaper. Introduction Control oflargespacestructures duringdeployment ofarticulated systems isofcriticalimportance. Allowing portions ofthestructure todeviate fromaprescribed pathcanresultinsnagging orimpact between surfaces thatcanprevent thestructure fromproperly deploying ormaycausedamage to satellite systems. Inthecaseoflargeinflatable spacestructures, mechanisms andspecific folding methods areusedtoprovide therequired controlofvarious partsofthestructure duringdeployment. Thesemechanisms andmethods aretypically simpleinnature,lowinmass,andsmall,keeping inline withgeneral spacecraft designpractices. Inflatable structures offerthepotential forlowermassandpacking volume forlargespacestructures such asantennas, solararrays,andsolarsailsascompared tocomparable mechanical systems. Thishas beendemonstrated instudies fortheNextGeneration SpaceTelescope, conducted byNASAGSFC (Figure 1).Theresultsofthesestudies leadtothedevelopment oftheISISflightexperiment, scheduled toflyin2001,toverifyperformance ofinflatable structures. Oneofthecriticalobjectives oftheISISflightexperiment istoevaluate theamount ofcontrolexhibited by theinflatable boomswhiletheyaredeploying thesunshield membranes. Theboomsmustdeploy linearly, provide structural support duringdeployment, andprovide anaxialforcetothemembranes to extractthemfromtheirowndeployment mechanism. Thisisaccomplished byamechanism thatis embedded intheendsofeachoftheinflatable booms, calledthewirebrake.Thewirebrakewas developed specifically forusewithspaceinflatable structures. *ILCDoverInc.,Frederica, DE Proceedings ofthe34_Aerospace Mechanisms Symposium, Goddard SpaceFlightCenter,May10-12,2000 231