Design and analysis on a kind of primary reflector support structure based on thermal compensation principle

Abstract

While the diameter of primary mirror becomes lager and lager, the accuracy of surface shape becomes extremely sensitive to gravity and temperature. The support structure has great significance to improve the imaging quality. The accuracy of surface shape can be improved by increasing the stiffness of support structure. However, high stiffness will decrease the structure's thermal stability. To improve the imaging quality under thermal environment, the structure should have reasonable flexibility. The problem is that, the support structure of a primary mirror can't keep both high rigidity and fine thermal stability. To solve this problem, a flexible and thermal compensation structure was introduced and the parameter was optimized in this paper. After the analysis of the surface accuracy by Finite Element Method (FEM) was carried out, the RMS value of surface precision decreased from the original 67.3nm to 12.6nm when the mirror working at thermal and self-gravity circumstance. The analysis results meet the requirement of the imaging quality. It indicates that thermal compensation structure can effectively improve the reflector's surface shape accuracy under the effect of the gravity and thermal load.