# HERMES CubeSat Payload Thermal Balance Test and Comparison with Finite Volume Thermal Model
## 3 Test Procedures
### Test Procedure  
The first step in the test procedure is to close the hatch and create a vacuum. The two stage pumping system is activated and kept on for the whole duration of the test. As the pressure stabilizes at \(3.5\times 10^{-6}\) mbar, the TVAC temperature control can be activated. The temperature at the interface between the payload and TVAC is imposed for three different set points: for each set point of the TVAC control, once steady-state is reached, the heaters are switched on and are kept active until steady-state is reached again. The voltage and current values of the heaters when switched on are reported in Table 1.  
ECSS does not impose constraints on the time gradient value for steady-state declaration [3]. Therefore, to avoid waiting more than one day for steady-state and due to oscillation in the cold temperature control of the TVAC, steady-state condition is declared reached whenever the mean of the time temperature gradient of the reference TC over 3 h stays below 0.01 \({}^{\circ}\)C min\({}^{-1}\) for at least one hour. Such value enabled confirming steady-state in 10 h, thus providing a test duration of 3 days for three set points. This assured the respect of the strict timetable of the inspection after the thermal test, imposed by scheduling constraints.  
The reference TC used to declare steady-state is tc1, located on the crystal box which is the most massive component of the payload, thus the one with highest thermal inertia: if  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**TC** & **Component** & **Position** \\ \hline tc1 & Cristal Box & Figure 5b \\ tc3 & PSU-PCB & Figure 7b \\ tc5 & TVAC Interface & Figure 9a \\ tc6 & FEE-PCB & Figure 5c \\ tc7 & BEE-PCB FPGA & Figure 5c \\ tc8 & Rib +z \(-\)y & Figure 10a \\ tc9 & PDHU-PCB & Figure 8c \\ tc10 & +x Panel & Figure 10b \\ tc11 & +y Panel & Figure 10a \\ tc12 & +y Shroud panel 1 & Figure 11a \\ tc13 & \(-\)x Panel & Figure 10a \\ tc14 & Rail +y +x & Figure 10a \\ tc15 & Rail +y \(-\)x & Figure 10a \\ tc16 & TVAC Base Plate 1 & Figure 10a \\ tc17 & +y Shroud panel 2 & Figure 11a \\ tc18 & TVAC Base Plate 2 & Figure 10a \\ tc19 & Top shroud 1 & Figure 11b \\ tc20 & Top shroud 2 & Figure 11b \\ \hline \hline \end{tabular}
\end{table}
Table 2: Thermocouples list.  
\begin{table}
\begin{tabular}{l l c} \hline \hline
**Entity** & **Equipment** & **Number** \\ \hline Temperature sensor & RS PRO Type T [37] & 19 \\ Temperature acquisition & Agilent 34970A [38] & 1 \\ Heater & Arcol HS10 [39] & 3 \\ Heater power supply & GW Instek GPS-43043 [40] & 2 \\ Heater voltage acquistion & National Instruments USB-6289 [41] & 1 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Test equipment list.  
such a component reaches steady-state it is reasonable to assume that also the temperature of all components is steady as well. In any case the steady-state condition is verified by the operator on the other components too, before moving to the next test phase.  
Due to laboratory access limited to working hours, a longer duration for the steady-state at the first set point was scheduled, as evident in all dates presented in Section 4. Test conditions and ECSS requirements are reported in Table 4.