Thermal ControlSimple AnalysisRadiative Heat TransferExampleDetailed FE AnalysisControl MethodsDesign ProcedureThermal Control•simple analysis•detailed analysis•control methodsSimple Analysis•spherical cow approach–simplify geometryapproximate spacecraftthermal inputs (external)thermal inputs (internal)thermal outputRadiative Heat Transfer•In steady-state, Qin = Qout [energy/time]•qin [energy/area/time]•from solar flux (S ~ 1.35kW/m2 at Earth’s distance from Sun) •Qin =  SAexposed + Qinternal ( = absorptivity)•Qout = qoutAtotal•Stefan-Boltzman Law: qout = T4 = emissivityExampleAexposedAtotalinternal sourcesQinternal = 100 W.Atotal = 4 r2, with r = 2 m.dist. from Sun = 1.25 au = 1.87108 km = 0.88  = 0.90Aexposed = 0.5 Atotal = 25.1 m2Qin = 100 W. + 0.88SAexposed(R/R)2 = 19184 W.Qout = T4Atotal  T = 294.2 oK = 21 oC = 70 oFrDetailed FE Analysis•Consider individual internal components (placement and thermal properties) and external geometry•TRASYS -- builds input file for SINDA•SINDA – calculates temperatures of componentsControl Methods•Passive–MLI (multi-layer insulation)–surface coatings–louvers–heat pipes•Active–electric heaters–thermal fluid loopsDesign Procedure•Develop list of requirements–min/max temperatures that components can tolerate–special thermal rqts for some instruments?•Estimate worst case hot/cold conditions–Initially, use simple steady-state analysis–Later, use FE analysis•Select and size thermal control