Research On Optical And Mechanical Design Of Low-light And Multi-spectral Imager

In order to establish a global indicator system for the sustainable development of the planet,it is necessary to integrate and analyze data including land,ocean,atmosphere and related human activities.Space remote sensing detection technology can acquire dynamic,periodic and multi-scale richness,which can be used as a "sharp tool" to obtain earth big data and provide strong support.In the face of the unfavorable conditions of low illumination and weak light,the low-light remote sensing technology has the same detection effect as the daytime under the weak reflected light of the ground,such as lamp,moonlight and starlight.And get a higher resolution night low light image.The development of low-light remote sensing technology and the development of space low-light imager can realize all-sky observation,broaden the effective working time of remote sensing satellites,and make up for the limitations between visible light and infrared channels.Therefore,the development of low-light level and multispectral imager involved in this paper can make up for the domestic facilities for low-light observation,provide feasible schemes and promote the development of related fields.The development of low-light multispectral imager,the main achievements of this paper include the following parts of work:1)Optical system design of low light level and multispectral Imager: By summarizing and analyzing the imaging principles of two imaging systems,namely,swing scanning imaging and push scanning space imaging systems,which are mainly used today,the refraction,retractable and total reflection optical systems are analyzed and compared,and the Cook-TMA off-axis triple reflection optical system,which adopts the large-width push scanning imaging system,is selected as the optical system of the imager.In addition,two single systems are used to achieve a wide width of300 Km and a resolution of 10 m through field splicing.Complete the optical design that enables the imager to achieve 10 m ground-resolution imaging at 505 Km orbital altitude,and obtain the optical system with small F number(F/5),field of view Angle17.2°×2.3°(single system)and focal length of 111 mm.In addition,in order to control the size and volume of the system,the method of interval control is adopted for the initial structural design.For the off-axis three-axis system designed by off-axis and deflection on the basis of the coaxial three-axis optical system,the Cook-TMA system with the system off-axis degree of 6.15° is optimized,in which the main three mirrors are the elongated mirror of even aspherical surface,and the secondary mirror is the aspherical surface.The designed optical system transmission MTF full field of view is better than 0.684@50lp/mm,the image quality is close to the diffraction limit,and the field of view is less distorted.2)The space environment of the imager is analyzed.In the process of going through the ground,launching into orbit and in orbit,the system needs to face the dynamic environment such as the change of gravity condition,the change of temperature field,vibration and acceleration impact.After the selection of mirror and supporting structure materials,supporting form selection and the design of the back structure and supporting structure of the mirror,the design of the mirror components is completed.For the main and third mirrors of the long mirror,the back single point flexible support is adopted,and the small diameter mirror is adopted the back center peripheral flexible support.For large diameter long mirror,the single point back support can be used,which can ignore the difficulty of setting the position of the support point in the design and research,but also improve the efficiency of mirror assembly and system installation,and because one mirror assembly only needs to process one support structure,the material and processing costs can be greatly reduced.3)The rigid body motion and surface deformation caused by optical surface errors under mechanical and thermal loads are analyzed,and the optical and mechanical integration method is explained for data conversion evaluation of optical properties using finite element analysis data.The light weight optimization of the long strip mirror is carried out,the parametric model of the mirror is established,and the multi-objective integration optimization is carried out on the multi-objective normalization processing by using the weighted method,so as to improve the calculation iteration of optimization efficiency.The influence of the axial position of the support on the mirror deformation was analyzed and the axial position of the support was optimized.Simulation analysis is carried out on the optimized main and three-mirror components to verify whether the mirror errors meet the requirements under the influence of dead weight and temperature field.The results of the natural frequency and dynamic response of the modal analysis components show whether they have good static stiffness and dynamic stiffness,and whether the structure damage occurs.4)The main frame of the single system adopts the separated low body aluminum-based silicon carbide front and rear plate frame and the M55 carbon fiber middle connecting support frame to meet the advantages of high stiffness and light weight.The two systems are respectively mounted on the satellite platform support plate through three-point rigid supports at specific angles.The finite element simulation analysis of the whole machine was carried out to verify the performance of the mirror assembly in the whole machine,including statics analysis,dynamics analysis,etc.,in each environment,the mirror assembly can meet the imaging parameters.How to describe the finite element analysis data in the optical software is studied,and the finite element data is processed into the optical system analysis,and the optical system under the working condition is verified.