Optimization of the mirror mounting structure for a reflective star tracker based on integrated analysis of line-of-sight thermal stability error

This paper investigates the thermal drift of the line-of-sight (LOS) resulting from temperature fluctuations during the on-orbit operation of a large-aperture, long-focal-length off-axis reflective star tracker. It aims to develop optimization strategies to improve thermal stability and LOS accuracy. A tolerance analysis of the optical system was first performed to quantify the impact of each optical component on LOS variation, with a specific focus on the primary, secondary, and tertiary mirrors. Subsequently, an LOS sensitivity matrix was constructed to correlate structural displacements with optical image point deviations. Based on this, the flexible support structures of the mirrors were sequentially optimized, resulting in a configuration that effectively reduces thermal drift. The results indicate that, following optimization, the LOS thermal drift angle decreased from 0.03499^{<i>'</i><i>'</i>}/^∘<i>C</i> to 0.02435^{<i>'</i><i>'</i>}/^∘<i>C</i> under a 5°C temperature increase, yielding a 30.4% reduction. The measured LOS thermal drift angle was 0.02641^{<i>'</i><i>'</i>}/^∘<i>C</i>, deviating by only 8.46% from the simulation result. Surface figure measurements showed that the respective surface errors of the primary, secondary, and tertiary mirrors were 0.015<i>λ</i>,0.017<i>λ</i>, and 0.014<i>λ</i>, all satisfying the star tracker's technical specification (<i>R</i><i>M</i><i>S</i>≤<i>λ</i>/50). Wavefront aberration measurements yielded RMS values of 0.066<i>λ</i>,0.068<i>λ</i>,0.073<i>λ</i>,0.072<i>λ</i>, and 0.069<i>λ</i> across five fields of view, conforming to the imaging system's technical specification (<i>R</i><i>M</i><i>S</i>≤1/14<i>λ</i>). The proposed optimization strategy enhances thermal stability, mitigates LOS thermal drift, and ensures that the final design fulfills the high-precision attitude determination requirements for space applications.