## 6 Thermal System Design
### Thermal Load Case Testing (SolidWorks)
An error arises when comparing results generated in SolidWorks to those generated in first-principle calculations. This is because SolidWorks does not account for the absorptivity of faces incident with thermal load and assumes full ideal absorption, whereas the first-principle accounts for absorptivity of the incident faces, for a weighted load into the system based on material properties. In SolidWorks, the model's material could be changed to rubber, for example, and this would have no bearing upon the results, highlighting the need for the future development of a transient model [9]. The range of temperatures exerted during the hot phase is unacceptable as many of the electrical systems components would fail under the calculated thermal load [9]. For example, this temperature would lie outside the safe operating range of the CubeSat's selected battery, causing potential catastrophic failure for the imminent eclipse phase when stored power is required to operate vital sub-systems. It is, therefore, necessary to introduce an additional thermal passive control system,  
Figure 51.1 Alteration of the Thermal Loading for Steady-state Heating Cycle. for example multi-layer insulation, to help shield incoming critical components from incoming radiation [9]. A following thermal study was conducted, investigating the impact of the \"eclipse phase\" upon the internal temperatures of the CubeSat. Initially the original material parameters used in the first-principle steady-state calculations were applied. A flux of (198 Wm\({}^{-2}\)) was applied to Earth-facing edge, with radiation to background space assumed for the other remaining 5 faces. The minimum temperature, illustrated in Figure 57 observed during this analysis was 183.3 K (\(-\)89.7 \({}^{\circ}\)C). When compared to the first-principle calculations result of 172.951 K (\(-\)100.0489 \({}^{\circ}\)C), the values are found to have approximately 10% difference. This is due to the slight differences in radiation emittance from the CubeSat body, as the first-principle calculations assume no emittance from the solar cell-mounted face incident with solar flux, whereas the SolidWorks analysis has been configured to assume heat loss from this face. When comparing the results to published literature [9] compass-1 encountered theoretical cold case temperatures of 167.7 K. The negligible difference in calculated results compared to those presented in literature highlights the accuracy of the developed thermal load case. To validate first-principle results incorporating a thermal load due to heat dissipation, a study was developed to replicate each respective hot and cold case in SolidWorks thermal solver. The finalized hot-case analysis mirrored the initial hot analysis, with the addition of a 0.7995 W applied to the \"top face\" to replicate a worst-case heat transfer scenario [9]. The minimum observed temperature is 321.2 K and the maximum observed temperature is 339.5 K directly upon the face incident with the incoming solar flux, which is to be expected as the highest incoming rate of energy is located at this geometry, shown in Figure 51.2 The average observed temperature throughout the structure is 330.35 K (57.35 \({}^{\circ}\)C) which represents an approximate  
Figure 51.3 Steady-state Cold Case Testing Results. temperature increase of (4.5 \({}^{\circ}\)C) which is to be expected due to the additional thermal load placed upon the structure [9]. The calculated value is extremely close to the 326 K experienced by compass-1 under an extremely similar thermal load, validating the accuracy and reliability of the generated results [9] The addition of a thermal heat dissipation load has further increased temperatures inside the structure, increasing the need for a thermal management system to be incorporated to bring this temperature to a safe operating level. The cold case power dissipation simulation also provided extremely similar results to those published in literature.