Research On The Lightweight Design And Compound Support Of The Large-aperture Mirror For Space-based Telescope

With the continuous improvement of the space exploration resolution, the aperture of space camera’s primary mirror is bigger and bigger. As the diameter increases, the mirror component is more sensitive to the interference of the changes in gravity and temperature and the environmental conditions for the launch and transport. In view of the function demand, the complexity of the work environmentand its lack of maintainabilty of the space remote sensor’s large aperture mirror component, the mirror component must have high dimensional accuracy, high reliability and high stability.In this paper, based on the stable support of the 2m diameter primary mirror of the large-scale integrated space telescope project under research, the research work of the following aspects is carried out:1)Based on an overview of lightweighting design of the large aperture mirror and the development of support structure at home and abroad, the advantages and disadvantages of all kinds of support structure are introduced in detail and the development direction of space-based large aperture mirror support is concluded.2)In view of high dimensional accuracy, high reliability and high stability requirements of the space-based large aperture mirror, the active-passive compound support structure, with mainly passive support and active support as auxiliary to the main, is put forward. Passive support is composed of peripheral support and back support, while active support is made up of 36 force actuators. In normal working state, passive support works, with the combined function of the peripheral support and back support, to constrain the six space freedom degrees of the primary mirror and realize the static determinate support so as to realize the space positioning of the primary mirror and through the multipoint support of the peripheral and back support, ensure the surface shape accuracy of the mirror surface. During the period of on-orbit working, when the passive support system doesn’t work due to unpredictable factors such as temperature control disorders, the active support works. At this point, the passive support works as "hard point" for the spatial location,while the active support works on the surface shape adjustment for the primary mirror by the force sensor, force-applying mechanism and control algorithm, to guarantee the normal work of the primary mirror component.3)In this paper,a new integrated optimization design method for large-aperture space-based mirror component is put forward.The traditional design of the mirror lightweight and support structure mainly adopts traditional experience design and means of checking by finite element method. This method is based on the experience of the designer, with the traditional theory and empirical formula to design the structure of the mirror components, to check it with finite element method, and then according to the result of simulation analysis, to modify the model with iterations, and finally complete the design of mirror component that meets the index requirements. This method is of relatively low efficiency and costs a lot of manpower and material resources. The design results are difficult to converge to the optimal solution, and the design result can only meet the local optimal solution of design index. It is difficult to get the global optimal solution. Aimed at the defects of traditional design method, a new method of mirror component optimization design is put forward in this paper, that is, the combination of traditional experience design, the topology optimization design and the parameter optimization design, a comprehensive optimization design method. This approach to design is of high efficiency and high convergence speed of results and can quickly get the structure with optimal performance.4)With traditional experience and the formula of classical theory, study support principle in-depth and complete the initial design of the mirror and passive support structure.5) Passive support scheme optimization design.According to the index requirements, determine the variables of the component optimization design, constraints and optimization objective function. Selection of optimal objective function is the key.The influence of the mirror surface deformation to the optical system imaging is especially obvious, so we determine mirror surface shape error as the optimal objective function, and determine the mirror surface shape accuracy rms value as an evaluation standard of mirror surface shape error. Use the matlab language to write the calculation program of the mirror surface shape accuracy rms value. Use the process integration and function of process automation of the commercial software Isight, establish the optimization platform for the updating, calculation and evaluation of geometry and finite element model, to achieve the size parameter optimal design of the mirror and passive support structure.6)Active optics is used to eliminate the aberration caused by unpredictable factors during the period of on-orbit working. The aberration is decomposed into astigmatism, coma, trefoil, defocus and so on. Coma is adjusted by secondary mirror, defocus by the focusing mirror and astigmatism and trefoil by the primary mirror. The design goal of the number and locations of the active optical actuators is the correct ability about the aberration component of astigmatism and trefoil.The Isight integration optimization platform integrated Sigfit software on the premise of multipoint of passive support as hard points, to complete the design of active optical actuator number and location.7)For validation about the active-passive compound support principle, the practicality of optimization design method and the engineering realizability of the scheme, the test mirror component is designed with the method by which the 2m diameter primary mirror component is designed and with the same scheme that the 2m diameter primary mirror component support adopt, the main principle experiment of passive support, the practicablity validation of the design method and the engineering realizability of the active-passive compound support scheme are carried out.Working around space-based large aperture mirror lightweight design and support technology, for the high dimensional accuracy, high reliability and high stability of the space-based large aperture mirror components, the compound support scheme with mainly passive support, active support as auxiliary is put forward; In view of the low efficiency of the traditional design of the space-based large aperture mirror components, and the disadvantages in getting the optimal solution, a new method of mirror component optimization design is put forward in this paper, that is, the combination of traditional experience design, the topology optimization design and the parameter optimization design,a comprehensive optimization design method. This approach to design is of high efficiency and high convergence speed of results and can quickly get the structure of optimal performance.Finally, by using the test mirror component, corresponding tests are carried out on the principle of the support scheme, engineering realizability of the support scheme and the practicability of the design method. This builds a solid foundation for the smooth development of the project under research.The compound support scheme and design method can be applied to the larger diameter space-based mirror support and design, and then, the backup active optical on-orbit application can be used as an early test of pure active optical on-orbit application, to guide on-orbit application of pure active optical.