Generalized Thermal Design Methods for Star Tracker on SSO Satellites

The thermal requirements for star trackers of SSO satellite are very stringent to guarantee the lower frequency error on the attitude due to thermal drift. An independent radiator is fixed on the satellite and thermally coupled to star sensor through heat pipes to provide cooling in the common scheme, which is complex and a unique thermal design is required for the same star sensor on different satellites. A generalized thermal control system for star trackers is designed and verified by thermal balance test and flight. Firstly, an integrated thermal approach is proposed in the paper. The radiator always exposed to cold space is mounted on the baffle of star trackers with thermal insulation pads and thermally coupled to star sensor through heat pipes to thermal dissipation. The direction of the radiator is consistent with the optical axis. Less solar heat flux is received by the radiator due to 30° sun rejection angle of star tracker. Then, enhanced thermal insulation design is used to reduce the influence of external thermal environment and heater loops with proportional control algorithm are adopted to decrease temperature fluctuations. Finally, taking APS star sensors mounting on remote sensing satellite as an example, the scheme is verified by thermal balance test and flight. The results show that, the temperature range of optical component and flange are from 18 ℃ to 22 ℃. The temperature gradient is less than 1.5 ℃ in the whole lifetime and the temperature fluctuation is less than 0.5 ℃/orbit. The validity of thermal control design is proved．