simple analysis detailed analysis control methods Thermal Control simple analysis detailed analysis control methods

Simple Analysis spherical cow approach simplify geometry thermal inputs (internal) thermal inputs (external) approximate spacecraft thermal output

Radiative 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  = emissivity

Example Qinternal = 100 W. Atotal = 4 r2, with r = 2 m. dist. from Sun = 1.25 au = 1.87108 km = 0.88  = 0.90 Aexposed = 0.5 Atotal = 25.1 m2 Qin = 100 W. + 0.88SAexposed(R/R)2 = 19184 W. Qout = T4Atotal  T = 294.2 oK = 21 oC = 70 oF r Aexposed internal sources Atotal

Detailed FE Analysis Consider individual internal components (placement and thermal properties) and external geometry TRASYS -- builds input file for SINDA SINDA – calculates temperatures of components

Control Methods Passive Active MLI (multi-layer insulation) surface coatings louvers heat pipes Active electric heaters thermal fluid loops

Design 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 method(s)