Long-term thermal stability of TianQin satellites

TianQin is a proposed space-based gravitational wave detection mission featuring high geocentric orbits. The strain sensitivity goal imposes stringent requirements on thermal control of the key science payloads, which relies heavily on the support of the satellite platforms. A main challenge for TianQin is the yearly varying sunlight directions with respect to the constellation plane. It leads to significant variations in the external heat flow, which is unfavorable for maintaining stable working temperatures inside the satellites over the long term. Based on a flattop sunshield design for the satellites and following passive thermal control guidelines, we propose a combined usage of multiple insulation materials, including polyimide foams and aerogel, at the sunshield and top plate of the satellite to enhance the thermal decoupling. The simulation shows that the temperature variation at the key payload bay can be suppressed within $\ifmmode\pm\else\textpm\fi{}0.7\text{ }\text{ }\mathrm{K}$ over three months, which is partly due to the lowered sunshield temperature by employing large areas of optical solar reflectors. Additionally, the design is also effective in damping down the thermal noise from the solar constant fluctuations in the mHz frequency band. The results can provide useful environmental input for studying temperature-related effects on the science payload performance.