# Optimization Design of the Spaceborne Connecting Structure for a Lightweight Space Camera
## 1 Introduction  
With the rapid development of the aerospace industry, remote sensing technology has been widely used in various fields of the national economy. At the same time, people put forward higher requirements for performances of space cameras [1]. The requirements of high performances mean that the camera has a large aperture and long focal length, which inevitably leads to the increase of camera mass and launch cost. Therefore, it is necessary to optimize the optomechanical structures of the camera so that it achieves a high lightweight ratio and meets space performance requirements [2]. The lightweight ratio of structures is the ratio of mass removed by optimization design to initial mass. The higher its value, the higher the lightness of the structure and the lower the launch cost of the space cameras. The spaceborne connecting structure of the space cameras provides installation interfaces for the space camera and satellite platform, and it reduces the influence of external loads on the camera. So, the optimization design of the connecting structure is very important for the development of a high-performance space camera. So far, there are two main types of connection between a space camera and satellite platform: vertical installation and horizontal installation. Vertical installation has the advantages of uniform force, good static mechanical performance, and it is not easy to be affected by external loads. It is generally used in space cameras with high lightweight ratio and low structural stiffness requirements, such as the Skysat-1 video satellite launched by Skybox [3], which is an American company, and Worldview seriessatellites developed by Digital Globe [4]. Horizontal installation has advantages of a low centroid of the whole satellite and a high satellite fundamental frequency. It is generally used in space cameras with high stiffness requirements, such as the Sofia Space Telescope designed by the German Aerospace Center [5]. In this paper, in order to ensure the suitable lightweight ratio of the camera and stability of mirrors, the vertical installation is adopted. There have been a lot of research studies on the optomechanical design. [PERSON], from the Lockheed Martin Space Systems company, designed precise bipod flexible support structures for the optical elements of NASA's IRIS spectrometer and realized the accurate installation of the optical elements. The bipod mounts successfully carried nine different optics through environmental testing and into orbit, which demonstrated the kinematic structures without fiction can be applied to most optic mount designs [6]. [PERSON] et al. proposed an optomechanical structure optimization method based on coupling sensitivity matrix analysis with an optimized telescope with an aperture of 600 mm and obtained a suitable lightweight ratio. Their idea is to reduce the number of iterations in a multi-variable structural optimization, taking advantage of the embedded sensitivity routines that are available both in FEA software and in ray-tracing software. It can be used simply for performance prediction or for optimization strategies [7]. [PERSON] applied Genetic algorithm (GA) to the truss-type main support structure of a space camera and realized a lightweight design of the main support structure. Genetic algorithm is a powerful tool to optimize a multi-objective optimization problem. They developed an optimization program employing a GA in order to obtain the main support structure design, which satisfies an acceptable homologous deformation with lightweight [8]. [PERSON] et al. wrote a program to process the deformation data of mirror surface nodes into a root mean square (RMS) value and optimized the mirror and its support structure with the RMS value as an objective. They used FEA to determine mirror surface deformation; then, the deformation surface nodal data were transferred into Zernike polynomials through MATLAB optomechanical transfer codes to calculate the resulting optical path difference (OPD) and optical aberrations.