isolatordescribedbyKlembczyk andMosher.First,boththehelicalspringandtheuniversal,zerofriction flexure,werenotincludedaspartofthedampingcartridgedefinition,andhencepartofthedamping cartridgecontract.Further,asthedampingcartridgeorificematureditwasdetermined thattheorifices throughthedampingheadwerenotrequired;rathertheannularorificebetweenthedampingheadand thecylinderwassufficient. Theprinciples,whichgovernthedampingcartridgeoperation,arestraightforward. Adampingheadis placedwithinanessentiallyclosedfluidfilledcylinder.Whenthedampingheadistranslatedrelativetothe cylinder,aviscousshearstressisgeneratedacrossthefluidthatexistswithintheannularorificecreated bytheclearancebetweenthedampingheadoutsidediameterandthecylinderheadinsidediameter. Widerangesofviscousdampingcoefficients areachievablegivensuchdesignvariablesasfluidviscosity, andannularorificesize.Thedampingheadissupportedonapistonrod.Asetoflabyrinthseals,which supportthepistonrodrelativetothecylinder,providetwocriticalfunctionsforproperdampingcartridge operation.Firstthelabyrinthsealisadynamicseal,i.e.,aninfinitefluidresistance, suchthatasthe dampingheadistranslatedinthecylinder,fluidflowsbetweenthetwofluidchamberscreatedonboth sidesofthedampingheadandnotthroughtheannularorificecreatedbetweenthepistonrodoutside diameterandthelabyrinthsealinsidediameter.Secondly,thelabyrinthsealsactaslinearjournalbearings suchthatlinearmotionofthepistonrodrelativetothecylinderispossible.Finally,theentireunitis hermetically sealed.Apairofweldedmetalbellowsisusedasflexuralsealssuchtheentiredamping cartridgeishermetically sealedrelativetotheexternalenvironment. Thetwofluidchamberscreatedby thebellowsassemblies areconnectedviaacrossoverport,suchthattherequiredfluidflowbetween thesetwochambersisaccomplished. Thefluidresistanceofthecrossoverportisnegligible. Thedrivingrequirements fortheSRTMdampingcartridgesaregiveninTable1.Thefinaldamping cartridgedesignsforthebendingandtorsionmodedampingmechanisms weremechanically identical. Theonlyrealdifferencebetweenthetwodampingcartridgesisthatthetorsionmodedampingcartridge wasfilledwith10cStsiliconefluid,whilethebendingmodedampingcartridgeswerefilledwith100cSt siliconefluid. Duringthedampingmechanism designphase,possibledampingcartridgefailuremodeswere considered, aswellastheireffectsontheoverallsystemstructuraldynamics,thefailuremodecredibility assessed,andrequiredfailuremodemitigations wereidentified.Specifically, threecartridgeoperational statesweredetermined: 1)nominaloperation,2)failuretoa"soft"condition,and3)failuretoa"stiff",or seized,condition.Nominalcartridgeoperationwasdefinedinthesensethat,asthecartridgewas "stroked",i.e.,thedampingheadtranslatedrelativetothecylinder,theforcerequiredforrelativemotion wasproportional totherateofrelativemotion.Dispersions allowedforundernominaloperationincludeda tenpercentabsolutetoleranceonthecartridgephysicaldampingcoefficientsuchthatthevariationofthe dampingcoefficient giventheoperatingtemperature rangerequirements wasaccounted forinthe structuraldynamicandattitudecontrolassessments. The"soft"failureconditionwasagenericfailuremodecreatedtodescribethesituationwhenthedamping cartridgestrokedreadily,butfailedtogenerateadampingforce,i.e.,aforcethatisproportional tothe rateofrelativemotion.Ahypothetical exampleofthisfailuremodeisarrivedifoneassumesthatthe dampingcartridgefluidleaksfromthecartridgeviaaweldmentcrack.Adampingcartridge"soft"failure duetoaweldmentfailurewasconsidered credible,basedaninabilitytoverifyweldmentworkmanship. XTable1.Damping Cartridge Requirements Parameter Bending Mode Damping Cartridge Stiffness (Ibf/in) 25 Damping 700 Coefficient (Ibfs/in) Stroke(in) 0.860 Frequency Range 0.05-2Hz (Hz)Torsion Mode Damping Cartridge 25 25 0.860 0.05-2Hz 89