## 1 Introduction  
With the increasingly important applications of modern space optical remote sensing imaging technology in civilian, military and commercial fields, there is a demand for optical systems with better resolution. Increasing the focal length of the optical system is the most direct way to improve its resolution, but this increases the system's aperture. A lightweight and large-aperture primary mirror is the most important optical component of a high-resolution space-to-ground remote sensing optical system. It needs to withstand complex and severe static during processing, inspection, assembly, transportation, dynamic loading, launch, and on-orbit work [1]. Under the above dynamic excitation, the large-scale structural dynamic response of the mirror causes changes in the internal stress state of its assembly structure, such as micro displacements, micro yield and internal friction, resulting in tilt and eccentricity of the mirror surface, deterioration of mirror surface accuracy and other issues. As a result, wave-front difference degradation and visual axis jitter error of the optical system occur, which affect its imaging quality and positioning accuracy; the entire optical system may even completely fail to image [2]. Therefore, it is necessary to conduct structural dynamic analysis of the entire main mirror assembly, evaluate its dynamic response characteristics and ensure that it has good dynamic characteristics. Modal and frequency response analyses of mirrors are important ways to study the dynamic characteristics of their structures. Modal analysis can help directly observe the vibration form of the mirror, which is the basis for structural dynamic analysis. The frequency response characteristics of the mirror can directly reflect the response of the mirror structure to external excitation, which is the focus of structural dynamic analysis. Accurate structural dynamic analysis results are based on accurate system modeling. The commonly used modeling methods for spacecraft dynamics modeling include distributed parameter, discrete coordinate, mixed coordinate, modal synthesis, and finite element methods [3]. Among these, the finite element method is most commonly used for structural dynamic analysis of space optical remote sensors. The finite element method is a general numerical method based on the variational method of solving boundary value problems of differential equations and on numerical approximation and discretization to solve the solution structure. Because of its good versatility and self-adaptability, the finite element method is becoming increasingly important for analyzing the dynamic characteristics of an optical system in scientific research and engineering analysis and also promotes the development of finite element analysis software. To improve computational efficiency, a simplified finite element model is usually proposed, as shown in Figure 1. The optical element is represented by a single node, but the single-point model can only predict the rigid body displacement of the optical element with three translational degrees of freedom and cannot represent the three rotational freedoms and its own elastic deformation. The calculation of shell element modeling is relatively short, but an important limitation of 2D element optical models is that they cannot predict the deformation effect through the optical thickness direction. Accurate system modeling is the premise to ensure the accuracy of analysis results. For lightweight mirror components with complex structures, 3D entity unit modeling is more realistic and accurate to analyze the results, but the scale of analysis and calculation is huge. Most scholars still use finite element analysis to analyze the dynamic characteristics of various structures [4; 5; 6; 7]. With the development of finite element technology, various finite element software packages have emerged [8; 9].