# Quasi-All-Passive Thermal Control System Design and On-Orbit Validation of Luojia 1-01 Satellite
## 2 TCS Design and Requirements
### Analysis of TCS Design Requirements  
The Luojia 1-01 satellite is a small satellite characterized by small volume, compact layout, a total mass is up to 22 kg, and the mass of the TCS is less than 1 kg. It works in a Sun synchronous orbit (SSO) and its thermal stability is poor, which in turn makes the satellite more vulnerable to the space thermal environment. In the meantime, due to the lightweight design of the satellite structure, the contact surface between the instruments and the satellite structure is quite small. Moreover, as shown in Figure 3, there are some shock absorbers made of low thermal conductivity material, majorly butyl rubber, between the \(\pm\)X panels and \(\pm\)Y and \(\pm\)Z panels, instruments and the panels they are meant to be mounted upon. As a consequence, the thermal conductivity is dramatically decreased on average. Coupled with the frequent shifting working modes of onboard instruments owing to the multiple work modes of the satellite, as a result, the temperature range fluctuation of the satellite is quite large. The general thermal design requirements of the Luojia 1-01 are listed in Table 6. From the table, it can be concluded that inside the cabin, the camera and battery have for critical temperature demands, since the mass and power allocated to the TCS design system is too inadequate to have as much active thermal control as it needs. Consequently, there a majority of onboard instruments cannot have active thermal control priority. This paper then presents a quasi-all-passive TCS by adopting the isothermal cabin design method. That means the camera and the battery are the only ones who can have active thermal control, the rest of the onboard instruments are exposed to all-passive thermal control. It's worth mentioning that no efficient heat transfer components like heat pipe can be used because of the satellite layout, mass and volume requirements. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Subjects** & **Contacting Form** &
\begin{tabular}{c} **Thermal Contact** \\ **Conductance Coefficient** \\ \end{tabular} \\ \hline Camera and satellite platform & Point contact/rough interface & 10 W/(m\({}^{2}\)-K) \\ Battery and satellite platform & Point contact/rough interface & 10 W/(m\({}^{2}\)-K) \\ Antenna stand and satellite platform & Point contact/rough interface & 10 W/(m\({}^{2}\)-K) \\ Structures and structures & Surface contact/smooth interface & 100 W/(m\({}^{2}\)-K) \\ Instruments and platform & Surface contact/smooth & 1000 W/(m\({}^{2}\)-K) \\  & interface/heat conductivity grease & 1000 W/(m\({}^{2}\)-K) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Thermal contact conductance coefficient between elements. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Materials** & **Thermo-Optical Properties** & **Thermal Conductivity** \\ \hline Aluminum coated polyimide film (one side) & \(\alpha_{s}=0.36,\epsilon_{H}=0.69\) & — \\ Argentum coated F46 film (one side) & \(\alpha_{s}=0.12,\epsilon_{H}=0.64\) & — \\
2A12 (Natural aluminum anodized) & \(\epsilon_{H}=0.1\) & 121 W\(\cdot\)m\({}^{-1}\)K\({}^{-1}\) \\ ZT4 (black coated) & \(\varepsilon_{H}=0.85\) & 8.8 W\(\cdot\)m\({}^{-1}\)K\({}^{-1}\) \\ T700 (black painted) & \(\varepsilon_{H}=0.92\) & 5 W\(\cdot\)m\({}^{-1}\)K\({}^{-1}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Material properties of the thermal subsystem. \begin{table}
\begin{tabular}{c c} \hline \hline
**Subjects** & **Equivalent Thermal Conductivity** \\ \hline MLI (20 units) & 0.04 W/(m\(\cdot\)K) \\ MLI (10 units) & 0.048 W/(m\(\cdot\)K) \\ Heat conductivity grease & 3 W/(m\(\cdot\)K) \\ Heat conductivity membrane (horizontal direction) & 1000 W/(m\(\cdot\)K) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Equivalent thermal conductivity of MLI and heat conduction materials. In a word, the Luojia 1-01 satellite is a small satellite characterized by low heat inertia, large temperature fluctuation, poor thermal conductivity, bad instrument heat dispersion and limited resources, including mass and power allocated for TCS.