Objective The main load-bearing cylinder is one of the most important supporting structures in optical remote sensing satellites, which plays a role in determining the relative position accuracy of the primary and secondary mirror. Its mechanical performance indicators have a significant impact on the imaging quality of space cameras. Due to the long focal length of large aperture space cameras and the large distance between the primary and secondary mirrors, the axial size of the main load-bearing cylinder increases. Moreover, during ground installation and testing, the main load-bearing cylinder is mostly in a cantilever state, in a relatively harsh working environment. Simultaneously, it must withstand dynamic excitations such as vibrations, impacts, and accelerations generated during the rocket launch process. As the main load-bearing cylinder accounts for a large proportion of the mass in space cameras, in order to meet the design requirements of structural lightweighting, it is also necessary to optimize the design of the main load-bearing cylinder. Therefore, designing a main load-bearing cylinder with a reasonable structural form, high lightweight ratio, and high stiffness has become an important part of the structural design of coaxial space cameras.
Methods Through the comparison of various material performance parameters, carbon fiber composite materials with high specific stiffness and low linear expansion coefficient were ultimately selected for the main load-bearing cylinder, and the basic structural form of the main load-bearing cylinder was designed (Fig.2). Then, finite element software was used for multiple load cases simulation analysis (Fig.5). Based on the analysis results, multi-objective and multiple load cases optimization design was carried out on the main load-bearing cylinder, aiming to reduce the structural mass while ensuring that the dynamic and static stiffness of the structure meets the design requirements. More reasonable structural parameters were determined through size optimization (Fig.7), the key structural layer parameters were improved through layer optimization. Finally, dynamic analysis and verification were carried out on the optimized main load-bearing cylinder, and the technical indicators meet the design requirements, improving the mechanical performance of the main load-bearing cylinder while reducing the structural mass.
Results and Discussions Before the optimization design of the main load-bearing cylinder, the displacement of the secondary mirror under gravity conditions was 9.15 μm, the first-order fundamental frequency was 196.3 Hz, and the overall mass was 14.3 kg. After size optimization, the first-order fundamental frequency was 220.6 Hz, and the rigid body displacement of the secondary mirror under gravity conditions was 5.96 μm. After layer optimization, the first-order fundamental frequency of the main load-bearing cylinder was 241.2 Hz, the maximum displacement of the secondary mirror under gravity conditions was 5.93 μm, and the maximum deformation under thermal load at 4 ℃ was 4.59 μm, all of which met the design requirements. The optimized overall mass was 12.6 kg. While improving the structural stiffness, the mass was reduced by 1.7 kg. After size optimization and layer optimization, a more reasonable structural form and layer parameters were determined for the key structure. The mechanical performance of the main load-bearing cylinder has been significantly improved.
Conclusions Taking into account the design indicators such as envelope size, dynamic and static stiffness, and overall mass, after optimization design of the main load-bearing cylinder, under the action of gravity, the displacement and tilt of the second mirror are 5.93 μm and 3.65″, respectively (Fig.9). The maximum deformation of the main bearing cylinder under a temperature rise of 4 ℃ is 4.59 μm (Fig.10). The x-direction and z-direction responses of the secondary mirror installation surface are 6.43 grms and 6.35 grms, respectively (Fig.13), which meet the design requirements of the main bearing cylinder. At the same time, the errors between the sine sweep frequency and random vibration test data and the finite element analysis results are within 3%, verifying the accuracy and feasibility of the optimization design method and simulation analysis process of the main bearing cylinder. The overall mass has been effectively reduced by 1.7 kg, with a decrease of 11.9%, providing a universal and effective method for the lightweight design and analysis of carbon fiber main load-bearing cylinder structures for large aperture space cameras.
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