Optimum structural design of lightweight silicon carbide mirror in Cassegrain system

Major efforts in space optics have inspired research in high performance, low cost, very lightweight reflective telescope systems in which Cassegrain system is widely used. Silicon carbide which has unique combination of attributes is used as the primary mirror material in this paper. According to the design requirement and processing technic of the mirror, and analyzing the effect of the sector, the triangle and the hexagon cell structures on the static and dynamic properties of the mirror, the triangle cell structure which has the best combination property is selected as the original scheme. Finite element method is used to build the parameterization model for the optimum structural design. The structure parameters such as thickness of the mirror and the faceplate which have more effect on the mass of the mirror and the maximum deformation of the mirror surface are selected as the design variables. After the optimization, a 256 mm diameter mirror with 24.5 mm thickness and 1.22 kg weight is gained. The lightweight ratio of the mirror is about 52.5 %, and the wavefront error (WFE) is satisfactory with the design requirements.