Optical And Mechanical Structure Design And Analysis Of All Aluminum Alloy Space Camera

With the continuous development and innovation of space technology,small satellites have gradually become the main trend of spacecraft development.Small satellites have the advantages of short manufacturing cycle,low launch cost,and easy networking to achieve high-frequency monitoring to meet the growing custom needs of users.Space camera is the core optical load of satellite,which undertakes the important task of optical detection.With the development of satellites towards faster design and manufacturing speed,smaller size and lighter weight,space cameras also need to shorten the processing cycle to achieve high miniaturization and lightweight.Aluminum alloy materials match the above requirements.Compared with common ceramic materials,the processing cycle of aluminum alloy space mirror can be shortened by more than 80%.However,the mechanical properties of aluminum alloy are low and the linear expansion coefficient is large.When the relevant imaging indexes of the system are improved,such as the decrease of the detection band and the increase of the camera aperture,the design difficulty of the optical mechanical structure of aluminum alloy increases sharply.Therefore,this paper studies the application of aluminum alloy in the optomechanical structure of space camera.The thermal performance of aluminum alloy is weak,so it is necessary to consider whether the allowable temperature range of the system can meet the requirements when it is applied to precision optical and mechanical structures.In the theory of thermal optics,there is no thermal difference in the reflective optical system of the same material.In this paper,all aluminum alloy optical mechanical structure design scheme is adopted.According to the specific imaging index of a space camera,the optical system is designed.Finally,the system adopts the R-C optical system with compensation lens group,the focal length of the system is 770 mm,the field of view angle 2ω=1.5°,the effective aperture of the primary mirror is 118 mm,and the wide band limit diffraction imaging of 400 ～ 800 nm is realized.The thermal characteristics of the actual optical system are analyzed.It is verified that the optical system of the same material can adaptively compensate the change of focal length and eliminate the thermal difference by matching the change of optical spacing and optical element surface.The optical and mechanical structure of the space camera is designed in detail.The change of mirror parameters has the greatest impact on the imaging quality of the system.The topology optimization and parameter optimization of 300 mm universal aperture integrated aluminum alloy mirror are carried out,and the support characteristics are analyzed.The effective characteristics of reducing the shape change of the mirror under the condition of self-weight are obtained,such as the central hexagon support structure.It is applied to the structure design of 128 mm primary mirror in the optical mechanical structure.The RMS can reach below 6nm(0.01λ).The main support structure is thin-walled cylinder,and the spoke bar is added to provide a fixed position for the secondary mirror.The back plate of the primary mirror is the main support body,and the primary mirror,the primary support structure and the rear light path components are embedded on the back plate of the primary mirror.The overall optical mechanical structure mass is 2.2kg,and the envelope size is ф162×300mm.The optical mechanical thermal integration analysis of the optical mechanical structure is carried out,and the environmental adaptability is explored by taking the imaging quality as the evaluation standard.Under different gravity conditions,the system MTF at Nyquist frequency is greater than 0.425.Under the coupling state of20±20℃ uniform temperature change and gravity,the system can meet the imaging requirements of MTF greater than 0.3 at 71.4lp/mm within the maximum temperature range.Combined with the actual thermal control layout conditions,the radial temperature difference is taken as the main standard in the gradient temperature field,and the allowable range of radial temperature difference is ± 1℃.In the vibration experiment of the structure prototype,the modes of tooling and camera in different directions are 110 Hz,117 Hz and 141 Hz respectively,which meet the requirements of system dynamics.In the thermal experiment,when the camera is in the thermal equilibrium state of 20℃ and 24℃,there is basically no axial temperature difference,and the temperature fluctuation is within ± 0.4℃,which indicates that the imaging quality can be guaranteed under the actual working conditions.In the system transfer function test,the camera has excellent image quality in the full field of view and meets the system index.Combined with the simulation analysis and experimental results,the relevant characteristics of all aluminum alloy optical mechanical structure are obtained.The advantages of all aluminum alloy opto mechanical structure in temperature adaptability are verified and the problem that the mechanical properties of aluminum alloy restrict the imaging quality is solved through the design of the back structure of the mirror.This project provides a reference for the application of aluminum alloy in visible light band space camera.