| As the core payload of remote sensing satellites,to design and study light-weight,small-sized,and high-performance space cameras is the key to accomplish small-medium satellites with highly integrated,low-cost,and cost-effective.On the premise of ensuring the excellent static and dynamic characteristics of the mirror system,and making it the lightest at the same time,the contradictory trade-off between the two makes the design of the mirror more difficult.Off-axis three-mirror space cameras are currently the preferred structural form of space optical remote sensors in various countries due to their advantages such as high lightweight,compact structure,long focal length,large field of view,and no obstruction.This thesis is aimed at the design of a medium-caliber off-axis three-mirror space camera,and its ultra-lightweight mirror assembly is designed.First,a variety of mirror surface fitting methods such as spherical fitting,homogeneous coordinate transformation,and Zernike polynomial fitting are introduced.The effects of the number of Zernike terms and the number of discrete points on the accuracy of fitting were studied,and a solution based on the SVD algorithm was proposed to eliminate the serious ill condition of the equations during the fitting process.The analysis shows that compared with the number of discrete points,the number of terms of the Zernike polynomial has a greater impact on the accuracy of the fitting.When fitting spherical mirrors,using 28 terms of the Zernike polynomial can ensure the accuracy requirements of the optical design.Combined with the outline size of the primary mirror,the form of back center support is adopted.The combination of topology optimization and multi-parameter size optimization is used to carry out ultra-lightweight design of the primary mirror body,and the primary mirror structure with the best performance and lightest weight is obtained.Aiming at the problem of insufficient rigidity of the single-point center support,a support structure suitable for the primary mirror was designed,and the influence of the diameter of the bolt connection ring on the surface shape and dynamic characteristics of the mirror was analyzed and discussed.By comparing with the mirror designed by traditional experience,the lightweight ration of the primary mirror designed in this paper is improved by 14%,and the performance index is better than that of the traditional mirror.Finally,the response of the main mirror assembly under the excitation of external dynamics is analyzed and verified.The tertiary mirror adopts the form of three-point support on the back.The size of the support hole is optimized and analyzed by the support form.Analogous to the method of optimizing the structure of the primary mirror,the ultra-lightweight optimization design of the tertiary-mirror mirror body is performed.Secondly,the back support structure of the tertiary-mirror is designed.For the rigid support structure that cannot take into account the shape of the tertiary-mirror under the thermodynamic conditions,based on the rigid support structure,the optimization analysis of the flexible form and specific parameters is performed.Finally,the performance of the designed tertiary-mirror module is checked.The initial structure of the back panel was designed based on the outline dimensions of the primary and tertiary mirrors and the requirements of the index.The top panel was optimized for lightweight design.The final back panel mass is only 12.81 kg,and the lightweight ration is 81 %.The total mass of the primary-tertiary mirror module is only 23 kg.Including the primary mirror assembly is 5.39 kg,the tertiary mirror assembly is 4.81 kg.In order to verify the performance characteristics of the subsystems designed in this paper,static and dynamic tests are performed on the primary-tertiary mirror assembly.The mirror surface shape of the primary mirror and the tertiary mirror under the coupling of gravity conditions and 4 ℃ temperature rise conditions are 6.96 nm and 11.1nm,respectively,which meet the design requirements.The first-order natural frequency of the component reaches 189 Hz.The response and stress also meet the strength requirements under overload and random vibration. |
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