Precision Radiative Thermal Control for Space Camera Mirrors on Micro-Satellites: From Ground Testing to On-Orbit Flight Demonstration

As the spatial resolution of micro-satellite optical cameras increases, reflective mirrors become highly sensitive to orbital thermal disturbances, where minor temperature variations may cause focal shift and optical modulation transfer function (MTF) degradation. Mirror thermal control of some satellites must achieve long-term stability within ±0.05 °C under stringent platform mass and power constraints. In a coaxial reflective camera, the secondary mirror assembly (SMA)—characterized by compact dimensions, low mass, and small thermal inertia—presents the primary stabilization challenge. In this study, an integrated active–passive thermal control system and a trend-based control algorithm are developed. First, an on-orbit eclipse attitude maneuver increases the orbit-averaged entrance aperture heat flux by 43 W/m2, mitigating external thermal shocks. To ensure high measurement accuracy, a dual-disc heat-loss-compensated heat flux meter (calibration deviation ≤ 1.37% across 200–426 W/m2 and 5.68% at 169 W/m2) and precision thermistors (curve-fitting residual < 0.001 °C) are calibrated in a cryogenic vacuum environment. Furthermore, non-contact flexible graphene radiative heaters are deployed using a discrete trend-based algorithm. By optimizing the control cycle to 1 s with a 0.1 s pulse resolution, ground thermal vacuum tests show the half peak-to-peak value of SMA temperature within ±0.042 °C under ≤0.5 W heating power. Finally, on-orbit telemetry confirms SMA temperature stability within a half peak-to-peak variation of ±0.04 °C with an RMS deviation ≤0.025 °C during the reported observation period under the tested orbital conditions at a rated power of 0.5 W. These results validate the high precision, ultra-low power consumption, and engineering feasibility of the proposed thermal management scheme for micro-satellite optical payloads.