# Design and Evaluation of Flexible Support Based on Space Mirror
## 1 Introduction  
Nowadays, the space remote sensing payload has entered a stage of rapid development, which puts forward higher and higher requirements for its resolution, while increasing the focal length and throughput aperture of the optical system, which are effective ways to improve the resolution of the ground image element. Therefore, in recent years, a long focal length and a large aperture are becoming the development trend of the space remote sensing payload, and consequently, the ratio of the mirror area and the perimeter are becoming larger and larger, thus the design of the mirror component becomes the most essential in restricting the development of the space remote sensing payload, and it is also one of the most urgent problems that needs to be changed [1; 2; 3]. In the space field, two types of support for mirrors are mostly used: peripheral support and backside multi-point support. The peripheral support presses the mirror into the frame through the pressure plate, and the mirror is fixed with adhesive around the mirror. This form of support is simple and convenient, and is generally applicable to small-diametermirrors. For medium- and large-diameter mirrors with diameters larger than 350 mm [4], peripheral support will increase the structural size on the one hand, which is not conducive to the lightweight and small-sized design of space remote sensing loads, and on the other hand, it is also difficult to obtain high face shape accuracy. Backside multi-point support connects the back of the mirror with the support structure through appropriate connection methods. Compared with the peripheral support type, the backside multi-point support is easier to obtain higher surface shape accuracy, so the backside multi-point support is often used for medium and large aperture mirrors [5]. With the backside multi-point support mirror component, the mirror and support structure need to have good stiffness to cope with the large number of mechanical vibrations brought about by the transportation during the launch phase. At the same time, the mirror and support structure also need to have a lighter weight and better thermal unloading capability to cope with the complex and variable temperature environment during the on-orbit operation. It is theoretically contradictory to have both strong stiffness, a light weight, and flexible temperature in the unloading structure. Therefore, finding a balance and a compromise among the contradictions, so that the index of the mirror component can reach an optimal solution, becomes the key to the design of the support structure of the mirror component. The objective of this paper is the secondary mirror component in an optical system, which is located at the farthest end of the optical system, which needs a higher standard to facilitate a more challenging mechanical environment as well as a wider range of thermal environment than other components. The surface shape of the secondary mirror will directly affect the imaging quality of the whole system. As the most remote optical glass component requiring light weight, the optical component needs to have a very high surface stability to accommodate the wide range of temperature variations, as well as a very high structural stability when facing a large order of magnitude of the mechanical environment [6]. However, light weight, high stiffness, and thermal stability will cause mutual repulsion; therefore, a reasonable design is to seek a delicate balance in the contradiction, so that its technical parameters can meet the requirements. Detailed descriptions incorporated in this paper consist of the selection of mirror materials, the layout of the support points of the mirror, and the design of the flexible support structure, with lighter weight, higher stiffness, and more stable face shape accuracy as the primary objectives.