Thermal Design of the Solar Array in a Low Earth Orbit Satellite by Analytical and Numerical Methods

Transcription

1 Thermal Design of the Solar Array in a Low Earth Orbit Satellite by Analytical and Numerical Methods Korea Aerospace Research Institute Hui-Kyung Kim*, Jang-Joon Lee, Bum-Seok Hyun and Cho-Young Han

2 Background Background and Objective Solar array converts solar energy into battery power Battery power is the major power source of satellite The on-orbit temperature of solar array affects directly the solar array efficiency Objective To determine the thermal design of the solar array side Analytical approach of 1D thermal resistance network for the temperature of solar array Four() type possible ideal surface finishes Select the optimal surface finish to conserve the allowable temperature limits of solar array To predict the on-orbit temperature of the solar array Compare analytical and numerical approaches based on the real thermal properties of the selected thermal design

3 Analytical Approach (1/5) Analytical Method to predict the temperature of solar array Assumptions for simplification The external heating environments of solar and side The optical properties of solar and side Irradiation to deep space (0K) Solar Array Backside Solar Cell Side α ε α ε T Irradiation to deep space T Irradiation to deep space T Thermal Configuration of Solar Array

4 dt mcp dt 0 Analytical Approach (2/5) Analytical Method to predict the temperature of solar array Þ T Thermal balance euation 1-dimensioal thermal resistance network model A single lumped-mass assumption of solar array Steady state assumption = + -se A( T -T ) -se A( T -T = = sa( e e -se ) = AT A( sa( e s ( e Thermal Balance Euation and Induced Solution -se + + e AT ) ) = + + e ) ) mcp : Thermal capacity T T e a e a s : Solar array temperature : Incident heat rate on the solar side : Incident heat flux on the solar side : Incident heat rate on the side : Incident heat flux on the side : Deep space temperature : IR emitance on the solar side : Solar absorptivity on the solar side : IR emitance on the side : Solar absorptivity on the side : W / m K Stephan - Botzmann constant 2,

5 Analytical Approach (3/5) Satellite design conditions applied to the analytical solution The orbit conditions Orbit attitude Fixed-type solar array configuration Daylight : Sun-pointing, Eclipse : Nadir-pointing Heating environment = e = 0 Earth IR Orbit Conditions (Orbit attitude and External environment) = a = e = e Solar Earth IR Earth IR + a + a b Albedo Solar

6 Analytical Approach (/5) Usually thermal painting is adapted for thermal design of the side of solar array It is reuired to determine the optimal thermal painting as the surface finish of solar array side Four() type ideal surface finishes Solar Absorber, Flat Absorber, Flat Reflector and Solar Reflector Defined by extreme α(solar absorptivity) & ε(earth IR emissivity) combinations Worst hot conditions Solar flux : 120 W/m^2K Albedo : 0.35 Earth Irradiation : 29 W/m^2K à The solar array temperature is predicted for each ideal surface type by the analytical solution

7 Analytical Approach (5/5) Solar Reflector is selected from the analytical results White paint is the general thermal painting application as solar reflector The Analytical Prediction of the Temperature of Solar Array ( for Four Ideal Surface Finishes)

8 Solar Array Configuration Solar Array Structure One Solar Cell Figure Solar s mounted on Honeycomb substrate Coverglass : CMG/AR (Qiopti) Solar Cell : ATJ Cell (Emcore) Facesheet : M55J (#3800, 0 /+90 /+90 /0 ) Honeycomb Core : 1.0 PCF-3/8-5056P-0007P T=25mm Solar array side : white paint (SG12FD)

9 Solar Array Thermal Conditions Solar Array Configuration (in Mechanical Design Integration Model) Backside White Paint (SG121FD) Solar Cell Side (3 Fixed-type Solar Arrays) 3 fixed-type solar arrays : Sun-Pointing attitude during the daylight Optical property - Solar Cell α = 0.92, ε = SG121FD White Paint α = 0.39(EOL), ε = 0.88 Solar efficiency % (EOL) à The effect of Solar efficiency is included in solar α Solar array size - 1 solar panel : 20 X 100 (cm) or 527 solar s per panel Thermo-physical property - CFRP facesheet + honeycomb structure

10 Thermal Analysis Model System Level Satellite Thermal Model ( Geometric Math Model Configuration) Detailed solar array model is numerically analyzed in system level satellite thermal model - Solar thermal properties - Honeycomb substrate thermal properties - White paint side surface finish Time-varying temperature profile of solar array is obtained SA1 Detailed Solar Array Thermal Model SA3 SA2 SA1 SA2 Solar Array Node Definition (Top View) SA3

11 80 Analysis Results Comparison For the Satellite Design Conditions, Numerical result of solar array thermal model On-orbit temperature profile Analytical result of 1D thermal resistance network model Steady-state temperature for the daylight and the eclipse periods Solar Array Temperature for above two methods (Numerical Method VS. Analytical Method) Temperature (degc) Temperature (degc) Time (hr) 0 SA1 #1 SA1 #8 SA2 #1 SA2 #8 SA3 #1 SA3 #8 SA1 #1 SA1 #3 SA1 #5 SA1 #7 SA1 #8 SA2 #1 SA2 #3 SA2 #5 SA2 #7 SA2 #8 SA3 #1 SA3 #3 SA3 #5 SA3 #7 SA3 # Time (hr) SA1 #1 SA1 #3 SA1 #5 SA1 #7 SA1 #8 SA2 #1 SA2 #3 SA2 #5 SA2 #7 SA2 #8 SA3 #1 SA3 #3 SA3 #5 SA3 #7 SA3 #8 ( Eclispe) T ( Daylight) T = K = C + e = Earth IR = ( ) s e = a e Solar + e Earth IR + a s ( e + e ) = K = 70.6 C ( ) b Solar

12 Conclusion Analytical result could be used to access which thermal finish of solar array side is optimal. Detailed solar array thermal model is developed successfully and is used to predict the on-orbit temperature profile with time. Analytical approach, that is, analytical solution of 1-D thermal balance euation for satellite solar array conditions results in a good approximation of the on-orbit extreme solar array temperature which is comparable with the numerical result of detailed solar array thermal analysis.