# Thermal Optimization Design for a Small Flat-Panel Synthetic Aperture Radar Satellite
## 5 Verification of Thermal Design  
To verify the correctness of the thermal design, TVAC testing was conducted on the SAR antenna and the satellite, respectively. Temperature-controlled absorbing devices were employed to absorb the high-power microwaves emitted by the antenna, ensuring that the equipment was not damaged. Additionally, these devices also served the purpose of simulating space heat flux. Figure 9 demonstrates the space heat flux simulation method employed for TVAC testing. The SAR antenna is positioned facing a device equipped with absorbing materials, and heaters are affixed to the underside of the device to mimic the space heat flux along the normal direction of the antenna plane (i.e., the satellite's +Z direction). The thermal test is carried out in a vacuum chamber with controllable temperature, where a high-emissivity black coating is applied to the chamber walls. By adjusting the wall temperature, the  
Figure 8: The simulated temperature for the satellite: (**a**) support plate; (**b**) platform component. chamber can be transformed into a heat flux simulation device [29]. During the thermal testing of the antenna, the heat flux in the Z-direction of the antenna is simulated utilizing this particular approach. During the TVAC testing of the entire satellite, an infrared light array was employed as an additional measure to simulate both the direct solar radiation and the heat flux generated by the solar arrays on the satellite. Since the satellite is mounted upside down on the absorbing device via a supporting structure, the thermal deformation of the structure during thermal testing may potentially impact the satellite. Consequently, temperature control measures were implemented on the supporting structure to maintain them close to ambient temperature. Figure 10 exhibits the temperature curves of 24 T/RMs during the satellite TVAC testing. When comparing the results with Figure 7a, it is observed that under identical thermal conditions as those used in the simulation analysis, the temperature trough of the T/RM is approximately 2 \({}^{\circ}\)C higher, while the temperature peak is roughly 4 \({}^{\circ}\)C lower. This discrepancy, which arises due to the simplifications made in the simulation analysis, poses no significant impact on the satellite's operational performance in orbit. During the imaging process, the maximum temperature difference among T/RMs is 3.6 \({}^{\circ}\)C, exceeding the simulation analysis results. This discrepancy arises from the fact that the implementation of thermal control measures falls short of the ideal outcomes anticipated during thermal analysis. Based on the testing results, the energy consumption for temperature control of the antenna is indeed zero, attributable to the rational design of the TIM usage area. This is called a zero-power thermal design approach. Figure 10: T/RMs’ temperature during TVAC testing. Figure 9: Heat flux simulation system with absorbing material. Figure 11 illustrates the temperature curve on the support plate during the TVAC testing. Point 1 in the figure represents the temperature measurement point near the DCU and PCDU. Due to the operating components, the temperature of Point 1 is slightly higher than 20 \({}^{\circ}\)C under high-temperature conditions. Point 2 denotes the temperature measurement point at other undisturbed positions, while Point 3 and Point 4 are the temperature measurement points at the center of the support plate, which exhibit lower temperatures. Overall, the temperature of the support plate meets the temperature difference requirement of less than 5 \({}^{\circ}\)C, and the temperature curve in Figure 11 aligns with the simulated temperature. Table 5 displays the equilibrium temperature of platform components during TVAC testing, where the temperatures of multiple components of the same type are grouped together.