# HERMES CubeSat Payload Thermal Balance Test and Comparison with Finite Volume Thermal Model
## 3 Test Procedures
### Test Configuration
The recording of the temperature at this point is of particular importance, as it represents the main thermal interface between scientific payload and Service Module. Figure 8: Routing of all the wires connecting TCs and heaters. Figure 7: TCs on BEE and PSU PCBs. The payload is integrated with the mechanical interface support; a conductive pad (Laird TFlex 340 ([[https://www.laird.com/products/gap-fillers-thermal-interface-materials/gap-fillers/tflex-300/a15324-02](https://www.laird.com/products/gap-fillers-thermal-interface-materials/gap-fillers/tflex-300/a15324-02)]([https://www.laird.com/products/gap-fillers-thermal-interface-materials/gap-fillers/tflex-300/a15324-02](https://www.laird.com/products/gap-fillers-thermal-interface-materials/gap-fillers/tflex-300/a15324-02)) (accessed on 2 November 2022))) is applied below the interface to maximize the heat flow between the TVAC cold plate and the payload assembly (Figure 9b). After the pad application, the whole assembly is fixed to the TVAC base plate by means of four M4 screws, installed with a 2 N m tightening torque. At the end, TCs on the lateral panels, structure and base plate are applied as shown in Figure 10.  
The last preparation step consisted of the aluminum radiation shield (1 mm thickness foils) placement all around the PL (Figure 11a). The shield just lays on the TVAC base plate and it is correctly centred around the DM using reference marks on the base plate. Its role is to provide a simple and easily reproducible thermal radiation environment around the specimen as the dimensions and inner infrared emissivity of the shield are known. Measurable and easy-to-reproduce boundary conditions (BCs) are mandatory to replicate the whole test in a numerical simulation, needed to properly correlate the thermal model with the test results. In the absence of a thermal shield, BCs would be moved to the TVAC walls (i.e., base plate, hatch, shroud and face opposite to the hatch). In that case, the entire TVAC geometry should be numerically modelled to correctly simulate the radiative test environment. Furthermore, the infrared emissivity of the TVAC walls should be known as well to correctly  
Figure 10: TCs on structural components. DM is fixed with the TVAC baseplate. Figure 9: Thermal pad and TC at TVAC interface. model radiation fluxes. Since such data was unavailable, the adoption of a radiation shield, solved all the aforementioned uncertainties. The interior of the shield is covered with one layer of 0.127 mm thick Kapton tape whose emissivity in the infrared range is known with accuracy. The orange-colored Kapton layers stripes applied on the interior of the shield are well visible in Figure 10(a),b. The geometry is much smaller and simpler with respect to the entire chamber: the setup of the numerical simulation is eased, and the computational burden is relieved, for the number of discretized view factors to compute between the DM and the shield is reduced. Figure 10: TCs on shroud and power suppliers. Please note that the shield is not fixed to the base plate, but given the small thickness of the aluminium foils and given its small mass, it is not expected to heavily impact the time needed to reach steady-state. Due to the lack of TCs channels available and due to the configuration symmetry of the payload, TCs are placed just on one side of the shield, assuming that symmetrical faces experience the same temperature. Dedicated TCs have been placed on the top cover, as shown in Figure 11b, since the part is not bolted to the lateral walls, and due to the fact that the PL is not symmetrical in the Z direction. The assumption made for the radiation shield is confirmed by the fact that the side panel and top panel have almost the same temperature as reported in the top graph of Figure 4:0  
The proper measure of the BCs is critical for a correct model correlation. For this reason, measures at each boundary point have been acquired by two TCs for the sake of redundancy.