Design And Analysis Of Precise Adjusting Structure Of Exit Pupil Mirror For Large Space Camera

With the continuous development of space technology, space camera is playing a more and more important role in the national economy, and large field of view and high resolution have become the future direction of modern space remote sensor. Due to self-weight deformation, thermal instability and other issues of traditional lightweight aspheric mirror, large wave aberration is introduced into the optical system, thus the resolution of space camera is limited, and how to calibrate the wave aberration of large aperture primary mirror is one of the core problems of the development of high resolution space camera. Based on the principles of active optics, deformable mirror technology which can be used to calibrate the distorted wavefront and improve the imaging quality of the optical system effectively, has wide application prospect in large aperture space optical system. In order to calibrate the wavefront aberration caused by large aperture primary mirror, deformation mirror device can be applied to the pupil adjusting structure of space camera to compensate the wavefront aberration through accurate controlling of pupil mirror. The design of the precise adjusting structure of exit pupil mirror is the core problem in the design of the deformable mirror, of which the performance will directly affect the correction ability of exit pupil mirror, and is the key link to improve the resolution of space camera.The special and complex space environment requires that the pupil adjusting structure has excellent spatial environment adaptability. In order to cope with the harsh conditions, such as microgravity environment, changing temperature field and particle irradiation, the pupil adjusting structure must have good dynamic and static characteristics and thermal adaptability, meanwhile it must ensure that the pupil mirror has excellent surface quality and aberration correcting ability. In this paper, the design problem of the precise adjusting structure of pupil mirror for large space camera is discussed, the mechanical properties of different structures are compared, the main factors affecting the aberration correction ability of pupil mirror are studied, and a scheme of precise adjusting structure of pupil mirror is given, which is compact, simple, reliable and has excellent working performance. The main contents of this paper include the following aspects:1, the components of the adjustment structure of pupil mirror are described. In combination with the imaging features of two common space cameras, the application of the pupil adjustment structure is explained, and the layout in light path is given. Theoretically, the mathematical principle and working process of pupil adjusting structure are derived, and lay the foundation for its application. The specific design criterion of the adjustment structure of pupil mirror for space camera is given, and compared from different forms of deformable mirror, the structure with discrete actuators and continuous mirror is selected as its optimal form, and its components and corresponding key points for design are also given.2, the details of the design process of the pupil adjusting structure are given. The design ideas of the main structures such as mirror, actuator assembly, support base, and embedded parts are described respectively. The two kinds of supporting bases are put forward, including solid structure and rib-board structure. The material combination of the main parts is determined, considering the processing technology and the space environment adaptability. The exit pupil precision adjusting structure proposed in this paper has compact structure, fewer components and high system reliability, and the design provides a solid foundation for future research and optimization.3, the related factors that affect the performance of adjusting structure are studied, and the structure is optimized. Using finite element method, with the corresponding structure model build and space working environment simulated, the simulation analysis is carried out, and the mechanical properties and thermal characteristics of the exit pupil precise adjusting structure are obtained. What kind of space conditions should be emphasized and how to simulate them are discussed. From the perspective of dynamic and static characteristics and thermal adaptability, two forms of support base are compared. Referring to the support methods for space mirror, the influence of different support schemes on the adjusting structure is studied. The combination of solid support base made of CFRP and the method of three point back support is ascertained as the best support scheme for exit pupil mirror adjusting structure. It is pointed out that flexible structure plays an important role in the design of exit pupil mirror adjusting structure, and flexible structure is added to different main components, such as pushing rod and actuator base, referring to varieties of flexible structures in space camera. As a result, its spatial environment adaptability is improved significantly.4, the spatial environment adaptability and aberration correcting ability of the structure are studied. Using this structure, the flattening test is carried out under typical working conditions, including the gravity and temperature rise, and the results are approximate to standard plane. The exit pupil adjusting structure is used to fit the wave elements, corresponding to the first 36 order of Zernike polynomials, and the residuals are small, which shows that the structure in this paper can effectively correct the aberrations of medium and low order, and its aberration correcting ability can meet the requirements of space camera.