## 3 Results
### Mission Analysis
#### 3.1.3 Thermal Budget  
Temperatures in the thermosphere vary radically depending on the Sun's illumination. The dependence on solar activity and the cycles of shadowing illumination every day form a highly variable thermal scenario. On the other hand, electronic devices have a well-defined temperature operating range (Table 6). The platform is exposed to high temperatures when in direct line of sight of the Sun and, if not properly defined, to very low temperatures when shadowed by the Earth. The simulation takes into account as heat sources the direct Sun radiation, the reflected radiation on the Earth's surface (albedo radiation), the Earth's radiation or Earthshine, and the internal heat dissipation of the electronic devices when they are turned on. On the other hand, the satellite itself radiates heat to space depending on the surface and emissivity of the solar cells and other materials.  
Figure 8: \({}^{3}\)Cat-3/MOTS power budget. In blue is the instantaneous charge of the batteries (A-h) during 5 days of simulation. After an initial transition period, the scheduler takes command and the budget is more predictable because the activity and duty cycles of the devices are firmly controlled. The green, blue, and red levels are at 90%, 75%, and 25% Depth of Discharge (DoD), respectively. The total battery capacity is 20.8 A-h, in a configuration of two modules of 10.4 A-h.  
To better control the satellite temperature, a coating should be applied to the surface of the satellite to vary the coefficient of absorptance and emittance. The satellite's structure is covered with polished beryllium, which has an absorptance coefficient of \(\alpha=0.44\) and an emittance coefficient of \(\varepsilon=0.01\)[23], (p. 363). This coating is will help to increase the satellite's temperature that drops during eclipse periods (simulated instantaneous average temperature of the satellite, Figure 9). The polished beryllium has a medium absorptance coefficient, but an extremely low emittance coefficient. Another alternative explored was to apply a coating with higher absorptance in order to capture more heat, for example black paint (epoxy), \(\alpha=0.95\) and \(\varepsilon=0.85\)[23], (p. 363). The simulations, however, show a much lower thermal budget due also to the higher emittance of the black paint (Figure 10).  
As mentioned in Section 3. _C. Scheduler_, the thermal budget indirectly controls the battery heater which will power on independently of the scheduler if the temperature drops under certain levels to preserve the thermal range tolerance of the devices on-board.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**Operational Temperature (\({}^{\circ}\)C)**} \\ \hline Device & min. & max. \\
6U Chasis & \(-40\) & \(85\) \\ Solar panels & \(-40\) & \(85\) \\ EPS & \(-40\) & \(125\) \\ Batteries & \(0\) & \(45\) \\ ADCS & \(-40\) & \(80\) \\ OBC & \(-40\) & \(60\) \\ S-band TX & \(-40\) & \(85\) \\ Optical payload & \(-40\) & \(60\) \\ \hline \hline \end{tabular} EPS: electric power system.  
\end{table}
Table 6: Operational temperature (\({}^{\circ}\)C) of all devices on-board the \({}^{3}\)Cat-3/MOTS sensible of malfunctioning due to temperature changes. Highlighted in red, the batteries, are the most restrictive temperature conditions’ device.  
Figure 9: \({}^{3}\)Cat-3/MOTS thermal budget. In blue/red, instantaneous satellite temperature (\({}^{\circ}\)C) for a 5-day simulation. The red color shows the temperature when there is no solar eclipse. On the contrary, the blue color shows the temperature while in Sun eclipse periods. The satellite’s initial temperature has been set to 25 \({}^{\circ}\)C. There is a noticeable permanent regime temperature around 10 \({}^{\circ}\)C. The maximum temperature reached is approximately 27 \({}^{\circ}\)C and the minimum temperature 4 \({}^{\circ}\)C. The absorptance and emittance coefficients of the coating (polished beryllium) are 0.44 and 0.01, respectively.