Thedynamicimpedances oftherespectivedampingmechanisms weresizedinatwo-stepprocess.Also, giventheCATgeometry,andthemastmodeshapes,thesizingeffortforagivendamperwasuncoupled fromtheother.First,thestaticspringstiffnesswasdetermined asoutlinedabove,thatisthemechanical springstiffnessofthedampingmechanism wasadjusted,inthiscasereduced,untilapproximately half themodalstrainenergyforthemodeormodesofinterestwasconcentrated intheelementswhich represented thedampingmechanism. Relativetothebendingmodedamper,variationsonthisapproach werealsotriedanditwasdetermined thatacceptable resultswereachievedwiththeupperbipodstrut rigidandthelowerbipodstrutsoft.Specifically, thecumulative staticspringstiffnessofthebendingmode damperlowerstrutwasspecifiedtobe87kN/m(500Ibf/in).Thecumulative staticspringstiffnessofthe torsionmodedamperwasdetermined tobe4.4kN/m(25Ibf/in).Thesecondstepinthedamper requirement definitionprocesswastodeterminethedampingcoefficient. Asensitivityanalysiswas performed byallowingthecumulative dampingcoefficient foragivendampingmechanism tobe analytically variedfromzerotoinfinity.Oncetherootlocusassociated withthesystem'sstructural dynamicswasknown,themechanism dampingrequirement wasdetermined byselectingthedesiredset ofstructuraldynamics,i.e.,frequencyanddampingratio,fromtherootlocusplot.Therootlocusplotfor thebendingmodedampingmechanism isgiveninFigure7,seeUmlandandEisen2001forafurther discussionoftheSRTMstructuraldynamiccharacteristics. Notethatintherootlocusdiagramtheradial gridlinesrepresentconstantdampingratiocontours,whilecirclesrepresentfrequencygiveninradian/sec. Furtherthearrowshownnexttothelociindicatesthedirectionofincreasingdampingcoefficient. The cumulativedampingcoefficientforthebendingmodedampingmechanism wasdetermined tobe370kNs/m(2100Ibf-sec/in),implyingthatthedampingcoefficientforeachofthethreedampingcartridgesis120 kN-s/m(700Ibf-sec/in). Whilethedampingcoefficientforthetorsionmodedampingmechanism was specifiedtobe4.4kN-s/m(25Ibf-sec/in). 6 ' 0'3uFI 0.7,""",_,_.L". 09" ," '-'_-'¢ "_ s65:__4__4(3_t{_t88&(_! -_ ,,:',..-,_.:_ -2 k-" ,,"/J-;. o9'_",""<' -4 ,,""-L;; o7",.,,'"?'--:_ 0_"-j _.. ,0,3"_-1"_-- -12 -10 -8 -6 -4 -2 0 RealAxisI8.9 -..,,.'.08 06 / / 04,' t -_02; < 0 -02 -04 -06 -08 ,.-" 0"9-1 i -2 -15o7, o%oSo'4l YawMode__ "-2":,3_8:...................... _o____i........... . / ""Og""0"O.op -1 -05 0 RealAxis Figure7.Bending ModeDamping Mechanism RootLocusDiagram Damping Cartridge Design Atradestudywasconducted earlyintheSRTMdesignphase,firsttodetermine thenecessity foramast damping system, andthentodetermine anadequate damping system designconcept. Themastdamping approaches considered inthetradestudyincluded: activestruts,Coulomb friction dampers, andlinear viscous dampers. Alinearviscous damping approach wasselected basedonseveral factors: 1)passive energy dissipation, 2)simple design concept, 3)amenability toexisting analysis tools,and4)design heritage. Theviscous damping cartridges selected andusedinbothSRTM mastvibration damping mechanisms wereamodification ofahermetically sealed vibration isolator previously described by Klembczyk andMosher andU.S.Patent4,638,895. Theviscous damping cartridge contained withinthe vendor's vibration isolator readilymettheSRTMdamping approach selection criteria. Itwasexpected that several modifications oftheexisting damping cartridge designwouldbeneeded inordertomeetSRTM requirements, specifically thephysical damping coefficient, andtheoverallstroke, i.e.,lengthoftravel. Thereareseveral differences between theSRTMdamping cartridges asprocured andthevibration 88