# Thermal Control of CubeSat Electronics Using Thermoelectrics
## 3 Results and Discussion
### Temperatures Achieved with Thermoelectric Cooling  
In Figure 4a,b, the cold-side temperature that is produced by the thermoelectric module is presented, again as a function of the system's thermal resistance. Figure 4: Thermal resistance versus the cold-side temperature produced by the thermoelectric module. Black line represents the imposed cold-side temperature for the conditions where a thermoelectric module in combination with a radiator would perform equally as well as the radiator alone. Blue lines indicate the temperature when the thermoelectric system is beneficial, whereas red lines indicate the temperature when the thermoelectric module is detrimental. The legend indicates (in \({}^{\circ}\)C) how much the benefit/detriment is. (**a**) Presents data for the initial temperature of 25 \({}^{\circ}\)C and (**b**) shows the same analysis for 75 \({}^{\circ}\)C.  
The black line represents the imposed cold-side temperature for the conditions where a thermoelectric module in combination with a radiator would perform equally as well as the radiator alone. Blue lines indicate the temperature when the thermoelectric system is beneficial, whereas red lines indicate the temperature when the thermoelectric module is detrimental. In Figure 4a temperatures are presented for the initial CubeSat temperature of 25 \({}^{\circ}\)C, whereas in Figure 4b the initial temperature was 75 \({}^{\circ}\)C.  
For Figure 4a it is clear that for thermal resistance/heat removal conditions where thermoelectrics is of benefit, relatively low temperatures are enforced on the object being cooled. For example, for a thermal resistance of 0.6 \({}^{\circ}\)C/W (providing cooling of approximately 25 W and a \(\Delta T\) of \(-\)10 \({}^{\circ}\)C, according to Figure 3a), the CPU would be cooled to a temperature of approximately 30 \({}^{\circ}\)C. While this is in the middle of the recommended operational temperature range for (CubeSat) electronics, Figure 4a also implies that without the thermoelectric module--and using just a radiator--the CPU temperature would be approximately 40 \({}^{\circ}\)C. This is also a comfortable operating temperature for the electronics. Therefore, in this case, while the thermoelectric system would provide additional cooling, it is unlikely to be worthwhile to implement. The conclusion is however slightly different when the CubeSat has an initial temperature of 75 \({}^{\circ}\)C. In this case, since the electronics are already at a temperature at the upper end of the acceptable working range, thermoelectric cooling can be beneficial. For example, for a thermal resistance of 0.6 \({}^{\circ}\)C/W (and with cooling of approximately 14 W and a \(\Delta T\) of \(-\)20 \({}^{\circ}\)C, according to Figure 3b), the CPU would be cooled to a temperature of approximately 66 \({}^{\circ}\)C. Without the thermoelectric system, the CPU would heat up to a temperature of 86 \({}^{\circ}\)C, which is unfavorable and therefore might justify the use of a thermoelectric module. It is likely to be in this type of scenario were thermoelectric cooling--capable of cooling below ambient temperature--is likely to be of benefit. However, for the majority of CubeSat orbits, the initial CubeSat temperature is unlikely to reach as high as 75 \({}^{\circ}\)C, used in this part of the study. Therefore the use of thermoelectric cooling for CubeSats may only be applicable in a small number of use cases. That said, there are certainly other space-based environments where the ability to cool below ambient would be of benefit, e.g., on the Moon or Mars, during the day time. Indeed, thermoelectric cooling has already been demonstrated for such scenarios in the past, e.g., for the Mars Curiosity Rover. One scenario where thermoelectric cooling could be used on CubeSats, is for very precise and accurate temperature control of temperature-sensitive components, e.g., sensors and detectors. This is a common requirement on-board satellites, particularly for sensors with cryo-temperature dependencies in order to provide stable measurements.