Research On Space Segmented Mirror With Curvature Correction

In recent years,with the rapid development of astronomy,scientists’ demands for the resolving power of telescopes have continued to increase.Since the resolution of telescopes is directly related to the diameter of mirrors,the requirement for the diameter of mirrors has gradually increased.Restricted by factors such as rocket transportation capacity and fabrication cost,it is difficult for traditional monolithic mirrors to meet the increasing diameter requirements.Segmented mirrors have become the main means to solve this problem at home and abroad.Multiple sub-apertures are matching into a larger overall aperture by means of active optics.In the process of segmented mirrors matching,due to factors such as assembly and environment,the curvature consistency error of the segmented mirrors cannot meet the requirements of co-focus and co-phase.And the existing segmented mirror curvature correction technology is mainly aimed at ground-based segmented telescopes,the research and application about space segmented telescopes are less.In order to promote the development of space segmented telescopes in my country,the research on space segmented mirrors with curvature correction is carried out by the aspects of theoretical analysis,model derivation,structural optimization,and experimental verification.The main research contents and achievements are as follows:1.Aiming at the problem of opto-mechanical structure design for curvature correction,an evaluation method of opto-mechanical structure design is proposed based on Zernike polynomials.By solving the relationship between the nodes displacement of optical surface meshes and Zernike polynomial coefficients,this evaluation method is directly applied to topology optimization and parametric design of the opto-mechanical structure.2.Research the back structure of the segmented mirror.Firstly,through the comparative analysis of the actuation schemes for curvature correction,it is found that the actuation scheme of curvature correction of 6 points on the outer ring and 1 point on the inner ring introduces less error.Therefore the distribution of the actuating points on the back of the segmented mirror is determined.Secondly,the distribution of the reinforcing ribs on the back of the segmented mirror is determined by topology optimization.3.Research the segmented mirror support.Firstly,analyzes the support method of the actuation scheme of 6 points on the outer ring and 1 point on the inner ring.Secondly,coupling optimizes the segmented mirrors and supports.In this coupling optimization,it is found that the traditional optimization method is inefficient and difficult to converge due to too many structural parameters and complex models.In this regard,multiple surrogates for complex opto-mechanical structures are proposed,and the results show that the surrogates can effectively solve the problem that the optimization is difficult to converge.After optimization,the RMS of the surface error influenced by the gravity of the segmented mirror is reduced by 75.8%,the RMS of the surface error influenced by the temperature is reduced by 47.6%,and the correction error of the radius of curvature is reduced by 23.4%.4.Aiming at the actuation scheme of 6 points on the outer ring and 1 point on the inner ring,an elliptical flexible linkage curvature correction mechanism is proposed and the design is carried out.Firstly,through the comparison of multiple schemes,the elliptical flexible linkage form of the segmented mirror curvature correction mechanism is determined.Secondly,the stiffness model of the curvature correction mechanism is deduced from the elliptical flexible flexibility matrix.Thirdly,the multi-objective optimization of the curvature correction mechanism is carried out with the flexibility of the flexible working direction as the target and the stiffness of the curvature correction mechanism as the boundary condition.After optimization,the correction error of the radius of curvature is reduced by 22.5%.5.A prototype of a space segmented mirror with curvature correction is designed and the influence of possible factors on the experimental results is analyzed.Then the experiments are carried out to verify the effectiveness of the method and model proposed in this paper.The segmented mirror is the mainstream technical means for the development of large-aperture space telescopes.The development of this research has a certain guiding significance for the future development of space segmented telescopes in my country.