Optimization design of an integrated primary mirror for an infrared-visible space camera

The visible-infrared dual-band common-aperture optical camera enables both daytime visible imaging and nighttime infrared imaging, achieving all-weather target monitoring. As the largest optical element, the primary mirror's structural stability and surface accuracy critically determine imaging quality. In this paper, optimized design and experimental verification of the mirror assembly are conducted. First, decomposition indices, including aperture, mass, and fundamental frequency, were identified based on the optical system. Through a comparative analysis of common mirror materials, silicon carbide was selected for its high specific stiffness and lightweight properties. An integrated structure combining the mirror body and backplane was adopted to alter the force transmission path of the traditional three-point support. This design minimizes mirror shape errors induced by gravity or temperature changes. Second, based on the experience in lightweight mirror design, the initial structure was designed. By performing topology optimization on the initial structure, the material distribution pattern was obtained. Through a size optimization mathematical model, the integrated primary mirror structure was ultimately derived. Then, finite element simulations of the optimized assembly showed root-mean-square (RMS) values of the mirror surface shape error below <i>λ</i>/60 (<i>λ</i>=632.8<i>n</i><i>m</i>) under gravity, assembly error, and temperature variations. The total mass is 2.93 kg with a first-order frequency of 215.922 Hz. Finally, measurement of the primary mirror surface accuracy using the ZYGO interferometer showed an RMS value of 0.016<i>λ</i>. Vibration testing produced a first vibration frequency of 210.97 Hz. Both simulated and experimental values meet all performance requirements for the infrared-visible space camera.