# Thermal Optimization Design for a Small Flat-Panel Synthetic Aperture Radar Satellite
## 4 Thermal Analysis
Figure 7 illustrates the simulated temperatures of various components on the SAR antenna under extreme high-temperature conditions, including the coldest and hottest points on the TR/M, PM, WPCU, and the antenna mounting plate of all arrays. The figure depicts a working condition where imaging tasks are performed for 10 orbital cycles, followed by a period of 5 orbital cycles without any imaging tasks. The antenna attains thermal equilibrium after the 7 th cycle, indicating that the temperature ceases to rise further. The peak temperature of the T/RM reaches 33 \({}^{\circ}\)C, and the temperature fluctuation amplitude during a single imaging task is 16 \({}^{\circ}\)C. Notably, the temperature consistency of all components, including the T/RM, surpasses the design specifications by maintaining a variance of less than 3 \({}^{\circ}\)C. Upon comparing the four sets of curves, it is evident that, despite variations in the temperature rise among components during the imaging process, all components are capable of rapidly cooling down to temperatures comparable to that of the antenna mounting plate post-task. This is primarily attributed to the exceptional thermal diffusion capabilities exhibited by the mounting plate. It should be noted that during the establishment of the numerical model, the lumped parameter method was applied to each component, simplifying them into a sheet-like structure while neglecting internal details. The thermal load was directly applied to the shell of each component, which deviates from the actual location of the thermal load. Consequently, there may be slight discrepancies between the simulated and measured results regarding the temperature peak. \begin{table}
\begin{tabular}{c c c c} \hline
**Category** & **Item** & **Hot Case** & **Cold Case** \\ \hline \multirow{6}{*}{Orbital heat flux} & Solar constant [W/m\({}^{2}\)] & 1414 & 1323 \\  & Albedo & 0.3 & 0.3 \\  & Planetary flux [W/m\({}^{2}\)] & 247.4 & 231.5 \\  & Extreme orbital parameter for antenna & Beta angle 59\({}^{\circ}\) & Beta angle 87\({}^{\circ}\) \\  & Extreme orbital parameter for platform & Beta angle 87\({}^{\circ}\) & Beta angle 59\({}^{\circ}\) \\  & T/RM [W] & 39.6 (Imaging) & - \\  & PM [W] & 33.6 (Imaging) & - \\  & WPCU [W] & 9 (Imaging) & - \\  & Battery [W] & 476 (Imaging) & 3 (Constant) \\  & & 86 (Imaging) & - \\ Component power & DSU [W] & 55 (Transmission) & \\ consumption & DCU [W] & 25 (Imaging) & 15 (Constant) \\  & & 25 (Transmission) & 5.5 (Constant) \\  & MCU [W] & 9.5 (Constant) & 5.5 (Constant) \\  & RW [W] & 81 (Maneuver) & 2.5 (Constant) \\  & PCDU [W] & 108 (Imaging) & 60 (Constant) \\  & DTCU [W] & 16 (Transmission) & - \\  & ACU [W] & 80 (Imaging) & - \\  & NRU [W] & 8 (Constant) & 2.5 (Constant) \\ \hline \end{tabular}
\end{table} 
Table 4: Details of extreme operating conditions. Figure 6: Thermal analysis model: (**a**) antenna; (**b**) platform. Figure 7: The simulated temperature of the antenna: (**a**) T/RM, (**b**) PM, (**c**) WFCU, and (**d**) antenna mounting plate. Figure 8a illustrates the temperature distribution of the support plate under low-temperature conditions. The temperature level remains within the design specifications. The lowest temperature point is observed at the center of the structure, reaching a minimum of 15.4 \({}^{\circ}\)C, which aligns with the heater layout. Figure 8b illustrates the simulated temperature range of the platform components under extreme operating conditions (represented by the red section), while also presenting the corresponding permissible temperature range (represented by the gray section). Thanks to the reasonable arrangement of heat dissipation surfaces, the temperature of the components inside the platform is maintained at approximately 20 \({}^{\circ}\)C. This ensures ample design margin for each device while minimizing the thermal control power required for the support plate.