psi)wasestimatedtobebetween230°Cand250°C.ThelaminatingadhesivelayerofFEPintheheater softensandmeltsatapproximately 200°C.Giventheclosespacingoftheinconelheatertracesandthe actionofmeltingandflowingFEPadhesive,theheatingelementswereexpectedtocontact,burn,andfail atcriticaltemperatures. Ourobservations ofheat-damaged heaterssupportedthis.On-orbit,heaterfailure isamuchmoredesirablemodethansealfailure(assumingdeployment hasalreadyoccurred). Insummary,thedesignstrategytomakethesingletime-outcontrolschemeworkwas: 1)Highpowerinputwillensureactuationatextremeconditions 2)100%pinover-travelwillminimizeriskofover-pressurization 3)Heaterfailurewillstopheatinputbeforesealfailurecanoccur Problems withtheControl Strate,qy: Thecriticalassumption thatover-travel andheaterfailurewouldprevent paraffin release wasnottrue. Duringsurvival testing, inwhichpowertotheactuator isleftonindefinitely, heating continued 100%ofthe timeuntilsealfailureoccurred. Heaterfailurewasexpected totakeplaceatactuator temperatures of 200°Cto230°C. Theactualsurvival temperature oftheactuators wasfoundtobe260°Cto270°C, dueto extrusion oftherearseals.Theheaterdesignwasextremely robust, andnotevenpartialelement failure wasnotedfortheduration oftheprogram. Ironically, thisresistance tofailureundermined ourdesign assumptions andthecontrolstrategy. Theproblem wascompounded byatolerance stackerror,whichwasdiscovered afterthefirst15shipsetshadbeenintegrated. Theerrorresulted inagap(about0.127-0.178 mm[0,005in-0.007in])inthe areaoftherearsealwhenthepinisinthefullyretracted position. Thepresence ofthisgapmeanttherear sealcouldextrude, andparaffin couldescape atpressures below68.9MPa(10,000 psi).Theproblem couldbecorrected, butthesolution required removing 1.27mm(0.050in)ofthepinover-travel. This reduced themargins onsealsurvival duetoextended powerbyroughly 10%.Thisledustoperform testingonhowlongactuators couldsurvivewiththegapdiscrepancy, andwiththe1.27mm(0.050in)of reduced over-travel. Itwasduringthistestingthatwelearned theheaters werenotafailuremodetorely ontoprevent paraffin release. Theawareness thatthecontrolstrategy wouldnotworkoccurred lateintheprogram, almost25%through thesatellite production phase. Thespacecraft systems engineers hadthesoftware readytoprovide a fixed-duration powersignaltothepinpullers. Itwasnotclearwhatlevelofre-design and/orretrofitwould benecessary tosolvethisproblem. Weworked veryclosely withtheleadengineer ofthespacecraft company tofindaworkable solution. BothStarsys andourcustomer hadbeenaggressive aboututilizing asimple, low-cost release device. In oureffortstomeettheprogram's needs, wewereoverlyoptimistic inourassumptions abouthowto controlthedevice. Finally,thoseassumptions werenotfullyinvestigated untillateintheprogram. Solution oftheControl Problem Theproblem wasapproached intwosteps:Thefirstwastonarrow theexpected operating temperature andvoltage range. Thiswascarried outbythespacecraft company. Thesecond wasforStarsys to conduct abatteryofsurvival andactuation timeteststocharacterize theperformance ofthepinpullers. Theinitialvoltage rangewas22VDCto34VDC.Closeranalysis bytheelectrical teamshowed thatatthe timeofdeployment, thevoltage rangecouldbenarrowed to26to33VDC.Thisreduced thepossible powersupplied fromarangespanning 15.3wattstoarangeof9.4watts,oranalmost40%narrower powerrange.Theuseofvoltage regulators wasconsidered, but12individual regulators wouldhavebeen required duetowiringconfiguration. Thiswascostprohibitive andnotadesirable solution. Temperature rangewasreduced insimilarfashion. Changing deployment sequence onthespacecraft, andoperating thepinpullers earliernarrowed thetemperature range.Theexpected lowtemperature wasincreased from -65°Cto-40°C,and+65°Cremained asthehightemperature. 280