为了探索研究大口径轻量化SiC主镜的可行性,对比分析了各种主镜轻量化形式的优缺点,确定了主镜的支撑方式;然后,从理论上计算了轻量化镜体结构参数,设计了采用夹心三明治结构扇形轻量化孔形式的1.23 m SiC轻量化主镜。利用有限元方法分析了轻量化主镜在浮动支撑下的自重变形,两种工况下的面形分别为:PV=9.43 nm,RMS=2.5 nm;PV=16.7 nm,RMS=3.2 nm。分析结果表明,镜体的自重变形影响较小,可以满足要求。而由于SiC的热膨胀系数较大,热变形影响较大,在稳态温度场下,温度每相差1 ℃,镜面面形变化约为PV=40 nm,RMS=4.8 nm,说明为了达到了设计要求,必须对镜体采取热控措施。

In order to explore the feasibility of the large lightweight SiC primary mirror, the different lightweight forms were compared and a supporting way for the primary mirror was determined. After theoretically calculating the light weighted structure parameters, a sandwich structure SiC primary mirror with sector holes was designed. With the finite element method, the self-weight deformation for the lightweight mirror upholded by a float support was analyzed. Under the two different conditions, the mirror surface figures were PV=9.43 nm,RMS=2.5 nm and PV=16.7 nm,RMS=3.2 nm, respectively. The results indicated that the influence of the self-weight deformation is smaller while the thermal deformation is larger because of the large coefficient of thermal expansion of SiC. At steady-state temperature field, when temperature changes 1 ℃, the mirror surface figure changes PV=40 nm,RMS=4.8 nm. These results reported here suggest that the thermal control must be applied to the mirror.