Thermally driven focus control and on-orbit defocus compensation analysis for the ET Transit Telescope

The Transit Telescope serves as the core payload of the Earth 2.0 (ET) mission, whose scientific capability critically depends on imaging quality. During launch and orbital insertion, the telescope experiences vibration, gravity release, and orbital thermal environments. These loads induce defocus and degradation of imaging quality. Therefore, on-orbit defocus compensation is necessary. This study proposes a thermally driven focus control method to achieve active focusing. Through thermal-structural-optical coupled analysis, a calibration model relating temperature, displacement, and defocus is established. It identifies the structural regions most sensitive to focus changes. And micrometer-level focusing capability can be achieved through thermal control. Simulation results demonstrate that the proposed thermal focusing approach effectively compensates for defocus induced by launch and on-orbit loads. And it meets the imaging accuracy requirements of the Transit Telescope.