# Thermal Optimization Design for a Small Flat-Panel Synthetic Aperture Radar Satellite
## 2 Satellite Overview  
Table 1 displays parameters of the satellite. The satellite has an orbit altitude of 515 km, with its SAR antenna operating in the X-band frequency. It supports stripmap modes with resolutions of 0.6 m, 1 m, and 2 m, as well as a ScanSAR mode with a resolution of 10 m. In the stripmap mode with a resolution of 2 m, the imaging duration for each orbit cycle of the satellite can exceed 100 s. The satellite maintains an attitude in which its SAR antenna points towards the Earth during standby mode and swings sideways by 20\({}^{\circ}\) to 40\({}^{\circ}\) during imaging. Figure 1 illustrates the layout of the satellite, which appears flat overall. The SAR antenna is positioned at the top of the satellite platform, which consists of six external panels and two internal panels. The SAR antenna is exclusively connected to the +Z side support plate, and the satellite platform design prioritizes the SAR antenna, eliminating the movable components like hinges and support rods. This ensures superior flatness of the antenna plane, thereby attaining higher imaging quality. The satellite flies in the +X direction in orbit, which has a very small windward area, minimizing the flying resistance of the satellite. Designing the platform with the payload as the center will result in the platform size being close to the load, and the electronics distribution within the platform is loose. This provides possibilities for optimizing the layout design of the heater. \begin{table}
\begin{tabular}{c c} \hline
**Item** & **Parameter** \\ \hline Operating orbit & 515 km SSO \\ Platform size & 3.17 m \(\times\) 1.24 m \(\times\) 1.7 m \\ Antenna size & 3.17 m \(\times\) 1.06 m \\ Weight & 310 kg \\ Operating frequency & X-band \\  & Stripmap: 0.6 m@5 km \\ Resolution @ imaging width & Stripmap: 1 m@10 km \\  & Stripmap: 2 m@20 km \\  & ScanSAR: 10 m@100 km \\ Imaging duration & \textgreater{}100\#2 m (Stripmap) \\  & Lifespan & \textgreater{}5 years \\ \hline \end{tabular}
\end{table} 
Table 1: System parameters of the SAR satellite. The SAR antenna is divided into three arrays, each with identical layout and function. The array is composed of stacked layers, featuring twenty-four radiation units (RUs) on the outermost (+Z side) of the SAR antenna and an antenna mounting plate with an aluminum alloy honeycomb structure in the middle. Inside the antenna, there are several devices, including twenty-four T/RMs paired with RUs, and eight power modules (PMs), each responsible for energy distribution to three T/RMs. Each array is controlled by a wave position control unit (WPCU). Both T/RM and PM have high heat consumption during imaging. In addition, if the temperature difference between T/RM components on the SAR antenna is beyond 5 \({}^{\circ}\)C, the imaging quality is adversely affected. To achieve superior anti-vibration properties and enhanced on-orbit attitude control capabilities, the components on board are positioned as close to the center of mass as feasible. Two internal compartments divide the platform into three sections. The middle section houses a digital control unit (DCU), a power conditioning and distribution unit (PCDU), and a reaction wheel (RW), all of which exhibit significant long-term heat consumption. On both sides of the platform, propulsion systems (PSs) and batteries are arranged, which have a narrow temperature adaptation range. Additionally, there are antenna control units (ACUs), data storage units (DSUs), and data transmission control units (DTCUs), which  
Figure 1: Structural layout of SAR01A: (**a**) overview of in-orbit status, (**b**) view from \(-\)Y side (PS: propulsion system; DTCU: data transmission control unit; DSU: data storage unit; ACU: antenna control unit; DCU: digital control unit; PCDU: power conditioning and distribution unit; RW: reaction wheel; NRU: navigation receiving unit; MCU: measurement and control unit). are devices related to imaging and data transmission tasks and exhibit short-term heat consumption.