Research On Semi-active Optical Technology Based On Warping Harness

As the aperture of the telescope,the key equipment for astronomical exploration,increases,the surface errors introduced by external loads such as gravity and temperature on the primary mirror surface also increase.In order to effectively and cost-effectively correct these errors,a semi-active optical technique based on Warping Harness has been developed,which can correct spatial frequency errors close to zero in a simple and efficient way with the main mirror passively supported.This paper relies on the "Warping Harness-based Semi-Active Optical Technology" project of the National Natural Science Foundation of China to carry out research on the correction principle,correction method and applicability of semi-active optical technology to meet the demand of large-aperture primary mirror surface shape error index.The work was carried out and completed for the following aspects:(1)Explained the support form based on the development history of large-aperture telescopes;detailed the origin and development history of the semi-active optical technology according to the time line,and summarized the mode of action of the technology.The correction principle of the semi-active optical technology is derived from the mechanical level,and the correction force is correlated with the amount of mirror aberration change;an improved ridge estimation method combining ridge estimation and weighted least squares estimation is proposed to address the problem of accuracy degradation caused by the pathological state of the normal matrix in the least squares solution process;and an improved differential evolution method is proposed to solve the weight matrix and ridge parameters required in the iterative process of improved ridge estimation.(2)A new design method of mirror support system is proposed,i.e.,a comprehensive design optimization method of mirror support system combining structural dimension optimization with empirical design,and a mirror 9-point semi-active support system is established based on this method.The results show that the semi-active optical technology mainly has good correction ability for the first-order aberrations of the test mirror,such as first-order aberration,coma,spherical aberration,clover,four-leaf clover,five-leaf clover,etc.After correction,the aberration amplitude has more than 1 order of magnitude convergence,and the RMS value of the mirror is reduced to 12.4nm,which has obvious correction effect.(3)The first-order aberration correction capability of the semi-active optical technology was studied,including the adaptability to the change of the mirror support system parameters and the applicability to different types of primary mirrors.The results show that: the correction capability of semi-active optical technology for first-order aberration of mirrors increases with the number of mirror support points;at the same time,the deviation of the support system introduced by the design,processing and mounting errors has no effect on the correction capability of semi-active optical technology;for large-aperture mirrors of different materials,lightness and shapes,the correction capability of semi-active optical technology is basically unchanged,and after correction,the first-order aberration magnitude of each type of mirrors is higher.After correction,the first-order aberration amplitude of each type of mirror basically has more than 2 orders of magnitude of convergence.(4)Taking the GMT-type circular sub-mirror splicing telescope as an example,firstly,the orthogonal polynomial of the circular sub-mirror splicing mirror is derived based on the single-aperture Zernike orthogonal polynomial;secondly,the co-phase retention mode based on the change of the edge sensor position is derived based on the hard point theorem and the co-phase retention mode based on the change of the aberration of the splicing mirror is proposed,and the co-phase retention accuracy of the two modes is compared by finite element analysis.The results show that the RMS values of the residual surface shape of the splicing mirror are 149 nm and 4.1nm after correction by the two co-phase retention modes,compared with the co-phase retention mode based on aberration change of the splicing mirror surface,which requires less sub-mirror support structure and higher correction accuracy;then the semi-active optical technology is used to correct the residual aberration of the splicing mirror surface after co-phase,and the RMS value of the splicing mirror surface is reduced from 149 nm to 2.2nm after correction.After correction,the RMS value of the spliced mirror decreased from 149 nm to 2.2 nm,and the amplitude of the aberration of each order of the spliced mirror basically converged to below,which can be considered that the semi-active optical technique has excellent correction ability for the residual aberration of the spliced mirror after co-phase.In this paper,the theoretical derivation and simulation verification of the Warping Harness-based semi-active optical technique are carried out,and the results can show that the semi-active optical technique has a good correction capability for the low-order surface shape error of the single main mirror;for the spliced mirror,the semi-active optical technique has a good correction capability for the residual error of the mirror after co-phase,and effectively improves the adaptability of the mirror to the support structure.This study has some significance and reference for the future face correction of larger aperture monolithic or spliced telescopes.