# HERMES CubeSat Payload Thermal Balance Test and Comparison with Finite Volume Thermal Model
## 4 Test Results  
The data acquired during the test and the related post processing are presented in this section. It is here remarked that faded red stripes in graphs of the current section mark the time windows in which the heaters were switched on. The first graph reported in Figure 12 shows the actual performance of the TVAC control. It can be observed how the 0\(\,{}^{\circ}\)C set point was initially undershot by 10\(\,{}^{\circ}\)C and during the plateau it keeps oscillating with an amplitude of 8\(\,{}^{\circ}\)C (peak-to-peak) due to the relay controller explained in Section 3.3. Nonetheless, the hot control of the base plate is keeping the oscillations within 1\(\,{}^{\circ}\)C. The same plot highlights that one of the two TCs placed on the external radiation shield registered incorrect results. Indeed, tcl2 shows erratic behaviour in disagreement with tcl7 placed on the same component (more on that will be added in the next paragraphs). The bottom graph in Figure 12 (figure time format day/month-hour) shows how all the TCs placed on structural components registered temperatures close to each other within a 7\(\,{}^{\circ}\)C range. That means the structure components of the DM have good thermal conduction links among themselves and the heat flow coming from the baseplate is properly transferred among them. Thus the structure can be used as thermal sink in case of necessity as it is expected that the heat power discharged on it will be distributed in a uniform way without creating big temperature gradients. The bottom graph of Figure 13 reports the heaters power history whilst their effect on the boards on which they were placed can be easily noticed in the upper graph of the same figure. The power history graph reveals that the power channel pch1, delivered on the PSU-PCB, oscillates: that is most probably due to electrical resistance changes caused by temperature variations in the materials at the set points. Indeed, during the test the power generators switched from current limited control to voltage control. Whenever in voltage control configuration, the power supply is free to change the current value, that is not registered; thus during those oscillations the power values reported in the graph are not reliable. This is due to the fact that the power is computed by multiplying the registered voltage measures times the current values fixed at the beginning of the test and assumed constant. Nonetheless, oscillations are contained and the effect of the resistance variations can be neglected. \begin{table}
\begin{tabular}{l l c c} \hline
**Entity** & **ECSS req** & **Value** & **Achieved** \\ \hline Set Point 1 & - & - & 0\(\,{}^{\circ}\)C \\ Set Point 2 & - & - & \(-25\,{}^{\circ}\)C \\ Set Point 3 & - & - & 30\(\,{}^{\circ}\)C \\ Slew rate crystals & - & - & \(\leq\)1\(\,{}^{\circ}\)C min\({}^{-1}\) \\ Max Pressure & ECSS-E-ST-10-03C—5.5.4.2 [34] & \(1\times 10^{-5}\,\)hPa & \(1\times 10^{-6}\,\)hPa \\ Temperature accuracy & ECSS-E-ST-10-03C—4.4.3 [34] & \(\pm 2\,\)K & \(\pm 1\,\)K \\ Steady-state & ECSS-E-ST-31C—4.5.3.2 [3] & - & \(\leq\)0.01\(\,{}^{\circ}\)C min\({}^{-1}\) \\ \hline \end{tabular}
\end{table} 
Table 4: ECSS requirements and test conditions achieved. A quantitative view of the temperature jumps caused by the heaters heat dissipation--simulating the actual electronic heat dissipation--is shown in Figure 14. It is possible to verify how the 1.4 W delivered to PSU-PCB causes an increase of 44 \({}^{\circ}\)C on the board, and a corresponding increase of 20 \({}^{\circ}\)C in the crystal box. The gradient of the boards temperature has been computed to verify the actual time needed to reach steady-state. In particular, the average gradient over a sliding window of the last 3 h has been monitored, and steady-state declared when its value stays below 0.01 \({}^{\circ}\)C min\({}^{-1}\) for more than 1 h. Figure 15 reports the time to reach steady-state, computed as described.