## 5 Experimental Verification of Key Thermal Design  
To confirm the design effectiveness of TRM radiators, a space-simulated thermal vacuum (TV) test was performed using a dummy model of TRM assembly with radiators. Figure 17 shows the configuration of the TV test set-up. The test specimen comprises a dummy TRM assembly integrated inside the text fixture. The test specimen, except for the front side of radiators, was entirely covered with MLI, and it was conductively isolated from the chamber base plate to avoid an unnecessary heat outflow from the TRM. The heat dissipation of TRM was simulated by a test heater group with 160 W power capacity attached to various locations of the dummy TRM. The heater was also applied on the rear side of each radiator to simulate the incoming environmental heat flux. In the test, the graphite sheet was not applied to the TRM structure because the test objective was to primarily verify the heat dissipation performance of the integrated radiators.  
Figure 16: Spatial temperature differences (\(\Delta\)T\({}_{\mathrm{s}}\)) of (**a**) SAR radiating board (**b**) S/C honeycomb panels in SAR left-looking mode in hot environment (Case 1).  
The specimen was exposed to the thermal environment of \(-70\)\({}^{\circ}\)C controlled by a chamber shroud. The operating temperature of the radiators was maintained to 20 \({}^{\circ}\)C by the heater control to simulate on-orbit temperature conditions. The temperature reference point was located near the center of TRM to declare thermal stabilization, as when the temperature variation is less than 2 \({}^{\circ}\)C/h. The TV test was performed under a pressure level of \(10^{-5}\) torr. In the test, the \(\Delta\)T\({}_{\rm s}\) between the center of the TRM and radiator was the main factor to judge the effectiveness of the proposed thermal design.  
Figure 18 shows the temperature profile obtained by thermocouples when the specimen was thermally stabilized. In the thermal analysis, the orbital average heat dissipation of TRM assembly was approximately 4 W because it was operated for only 60 s during SAR imaging, although its power dissipation was 365 W. In the test, the constant heat load of 16 W was first applied to the TRM, which was a sufficiently high amount of heat load to simulate the orbital average heat dissipation. The TRM reached 25.4 \({}^{\circ}\)C, and the maximum \(\Delta\)T\({}_{\rm s}\) between the TRM and radiator was 2.8 \({}^{\circ}\)C. Meanwhile, the thermal analysis results shown in Figure 15 indicated that the maximum \(\Delta\)T\({}_{\rm s}\) value of TRM assemblies #1-#4 was 7.0 \({}^{\circ}\)C when the radiator temperatures were ranging from 24.0 to 29.4 \({}^{\circ}\)C. Table 8 also shows that \(\Delta\)T\({}_{\rm s}\) was less than 7.6 \({}^{\circ}\)C in all cases of SAR imaging operations. The thermal conductance value between the TRM and radiator, simply estimated from the heat load and \(\Delta\)T\({}_{\rm s}\) observed from the test, was 5.7 W/K. Subsequently, the heat load of 160 W was applied  
Figure 17: Thermal vacuum (TV) test set-up of dummy TRM assembly with radiators.  
to the TRM to observe further heat dissipation capability. The increase in TRM temperature was only less than 1 \({}^{\circ}\)C after 60 s, and the temperature was stabilized at 89.8 \({}^{\circ}\)C. The \(\Delta\)T\({}_{\rm s}\) at the stabilized temperature was 17.4 \({}^{\circ}\)C. The thermal conductance value between the TRM and radiator in this condition increased to 9.2 W/K as the radiated heat energy increases at higher radiator temperature. These test results indicated that the proposed radiator design had sufficient heat dissipation capability for thermal control of TRM assembly in on-orbit SAR imaging operation conditions.