Polarized-Light Difference Method and Equipment for High-Precisely Measuring Star Sensor Bracket Thermal Deformation Based on Laser Autocollimation

Star sensors are widely employed in spacecraft, yet their observation accuracy is seriously affected by the thermal deformation of the sensor bracket. A high-precision self-calibration method for measuring a star sensor bracket thermal deformation by the quasi-common-path polarized-light difference based on laser autocollimation was first proposed, and the measurement equipment was developed. Zemax and Comsol software were used to simulate the influence of window glass and glue layer on the measurements, respectively, then laboratory experiments and field tests were performed. The simulation and experimental results show that the proposed method can greatly reduce the influence of mechanical drift, vibration, and other factors on the measurements, and greatly improve the accuracy and stability of long-term measurements. A comprehensive measurement accuracy of better than $0.45''$ was obtained in the vacuum test environment over $- 2~^{\circ }$ C to $- 6~^{\circ }$ C. Long-term vacuum thermal cycling of the star sensor bracket of “Aoke-1” satellite showed that the thermal stability of the yaw and pitch were $0.09''$ /°C and $- 0.45''$ /°C, respectively, which met the on-orbit operation stability requirements of $1.0''$ /°C. This developed measurement method and equipment ensures the future observation accuracy of the “Aoke-1” satellite and provides a new method for high-precision measurement of the relatively small angle change between two surfaces in vacuum and high-low temperature environments.