## 3 New Thermal Design Strategy for S-STEP  
The primary objective of establishing a new thermal design for S-STEP is to ensure long-term high-resolution SAR imaging duration for 60 s regardless of the right- and  
Figure 3: Internal configuration of S-STEP satellite (DCU: digital control unit; RFU: radio frequency unit; PSU: power supply unit; TRM: transmit/receive module; STA: star tracker assembly; RW: reaction wheel; ISL: inter-satellite link; IAU: integrated avionics unit; SPAU: S-band power amplifier unit; XRFU: X-band RF unit; PCDU: power conditioning and distribution unit; GPS: global positioning system; STCU: star tracker control unit). Figure 2: Mechanical configurations of S-STEP satellite: (**a**) view from S/C \(-z\) side, (**b**) view from S/C +\(z\) side, and (**c**) exploded view. left-looking modes of an SAR antenna. In addition, the thermal design shall maintain all onboard components within their allowable temperature limits (Table 2) in extreme on-orbit thermal environments with minimal use of heater power. To accomplish the thermal design objectives, the heat of the high-power components, such as the TRM assemblies, power conditioning and distribution unit (PCDU), IAU, and battery, shall be effectively dissipated to the outer space. These are the main focuses of the proposed thermal design. To implement a \"lighter\" satellite, the thermal design is mainly based on passive thermal control approaches using surface coatings, MLI, and heat dissipation radiators. The use of thermal hardware that occupy some portion of the mass to some extent, such as heat pipe and doubler used conventionally [13], are avoided for S-STEP. \begin{table}
\begin{tabular}{c|c c c c c} \hline \hline \multicolumn{2}{c}{**Component List**} & \multicolumn{4}{c}{**Allowable Temperature Limits [\({}^{\circ}\)C]**} \\ \cline{3-6} \multicolumn{2}{c}{**Coperating**} & \multicolumn{4}{c}{**Operating**} & \multicolumn{4}{c}{**Non-Operating**} \\ \hline
**Category** & **Item** & \multicolumn{2}{c}{**T\({}_{\text{min}}\)**} & \multicolumn{2}{c}{**T\({}_{\text{max}}\)**} & \multicolumn{2}{c}{**T\({}_{\text{min}}\)**} & \multicolumn{2}{c}{**T\({}_{\text{max}}\)**} \\ \hline \multirow{9}{*}{Payload} & \multirow{3}{*}{TRM} & \#1 & \(-20\) & \(60\) & \(-30\) & \(70\) \\ \cline{3-6}  & & \#2 & \(-20\) & \(60\) & \(-30\) & \(70\) \\ \cline{3-6}  & & \#3 & \(-20\) & \(60\) & \(-30\) & \(70\) \\ \cline{3-6}  & & \#4 & \(-20\) & \(60\) & \(-30\) & \(70\) \\ \cline{3-6}  & DCU & \(-20\) & \(50\) & \(-30\) & \(60\) \\ \cline{3-6}  & RFU & \(-20\) & \(50\) & \(-30\) & \(60\) \\ \cline{3-6}  & & \#1 & \(-20\) & \(50\) & \(-30\) & \(60\) \\ \cline{3-6}  & & \#2 & \(-20\) & \(50\) & \(-30\) & \(60\) \\ \cline{3-6}  & & SAR antenna & \(-60\) & \(60\) & - & - \\ \cline{3-6}  & & (Radiating board) & & & & \\ \hline C\&DH & IAU & \(-20\) & \(50\) & \(-35\) & \(70\) \\ \hline \multirow{2}{*}{EPS} & PCDU & \(-20\) & \(50\) & \(-35\) & \(70\) \\ \cline{3-6}  & Battery & \(-30\) & \(60\) & - & - \\ \cline{3-6}  & Solar panel & \(-55\) & \(110\) & - & - \\ \hline \multirow{9}{*}{CS} & \multirow{3}{*}{S-band ant.} & \#1 & \(-40\) & \(80\) & \(-55\) & \(85\) \\ \cline{3-6}  & & \#2 & \(-40\) & \(80\) & \(-55\) & \(85\) \\ \cline{3-6}  & SPAU & \(-20\) & \(50\) & \(-35\) & \(70\) \\ \cline{3-6}  & X-band ant. & \(-40\) & \(70\) & \(-55\) & \(85\) \\ \cline{3-6}  & XRFU & \(-20\) & \(50\) & \(-35\) & \(70\) \\ \cline{3-6}  & & \#1 & \(-40\) & \(85\) & - & - \\ \cline{3-6}  & ISL ant.