Thermal Control Subsystem FF THERMAL CONTROL

Space Thermal Environment Qs : Direct radiation from the Sun Qe : Radiation from the Earth Qa : Solar radiation reflected back by the earth (Albedo) Qi : Heat generation Qps : Radiation to Space Qpe : Radiation to the Earth Qa Qps Qs Qpe Qe Qi Earth pic: http://palimpsest.typepad.com/frogsandravens/pictures/earth.jpg FF THERMAL CONTROL

Orbit Model Approximated ISS Circular orbit: Atitude (H) : Period (T) : Shadow angle ( ) : Shadow time (Ts) : FF THERMAL CONTROL

Orbit Model o Shadow Sunlight FF THERMAL CONTROL

1. Steady-State Approximation Assumptions: Steady State: dT/dt=0 Spherical satellite with thermal surface area A= 2.16m^2 so An=0.54m^2 Surface characteristic: Heat generration: 50W View Factors: 6) Direct Solar flux: 0 (Cold), 1399w/m^s (Hot) Results: Worst-case HOT: Tmax= 316.0 K Worst-case COLD: Tmin = 219.3 K Tmax-Tmin=96.7 K FF THERMAL CONTROL

2. Node Analysis Thermal Equilibrium Equation Qs Qe Qa Qps Qpe Conduction between Node i and Node j Radiation between Node i and Node j FF THERMAL CONTROL

Satellite Model for Node Analysis Surface 2 always look downward. Assume no width for each surface FF THERMAL CONTROL

Ex: Direct Solar Flux (Worst-case Hot) 0.616 0.788 FF THERMAL CONTROL

Worst Cases Worst-case Cold Worst-case Hot FF THERMAL CONTROL Earth pic: http://www.bc.edu/schools/cas/geo/meta-elements/jpg/new_earth.gif

Surface characteristics Inside of the satellite is painted with L-300 (Black) Conductivity between surfaces : K=0.06 FF THERMAL CONTROL

Simulink model (Node Analysis) FF THERMAL CONTROL

Simulation (Worst-case COLD) Temperatures [K] FF THERMAL CONTROL

Simulation (Worst-case HOT) Temperatures [K] FF THERMAL CONTROL

Results (Node Analysis) High temperature differences on surface 4 and 5 Use MLI to make thermal disturbances from outside smaller. Need to consider thermal control methods to make temperature higher. FF THERMAL CONTROL

Future works Thermal Control by using Thermal Control Elements so that Design Temperature range fits Permissible temperature range of components. More-nodes analysis for accurate simulation FF THERMAL CONTROL