Design And Optimization For Main Support Structure Of A Space Camera With Large Field Of View And Long Focal Length

Due to off-axis TMA optical system without the central obscuration,which can easily achieve the large field of view,high resolution and good imaging effect,it has been used as the optical system of space camera by the researchers worldwide.But,Because of asymmetric of off-axis TMA optical system,the design and alignment technology for the main support structure of off-axis TMA optical system space camera is very difficult around world.Beisdes,to make the space camera with the detailed investigation and mass screening funcations,it must be increased the field of view and resolution for optical system.But,the position accuracy of the optical components is asked more accurate within the large field of view and high resolution off-axis TMA optical system than in coaxial optical system;it makes a big difficulty to the design the main support structure of off-axis TMA space camera.According to the characteristics of the off-axis TMA optical system,whose primary mirror,three-mirror and folding mirror length are all more than 1200 mm,length to width ratio are all more than 3: 1,quality are all greater than 40 kg,the space length between primary mirror and secondary mirror is more than 1500 mm,this paper make deep study form following five field.1.The author has researched on all kinds of typical main support structures used on space camera worldwide and distinguished their advantages and disadvantages when applying on the off-axis three miroor optical systerms who has high resolution,wild field of view.Finally,truss structure is chosen in this paper.2.Topology optimization on truss structure is proceeded.Acoording to Solid Isotropic Microstructures with Penalization(SIMP),the author conduct multi-objective topology optimization and achieve desirable initial truss structure.Divide the truss structure into several key sub-structures,and reseach on influence of the truss size on the performance of the whole camera.3.Design of front frame.According to the optical systerm is proceeded,this paper come up with a front frame structure which can support not only fold mirror but also second mirror.Fistly,titanium alloy is selected to fabricate the front frame after compare among common materials which are applied on space camera.Secondly,a topology optimiztion based on contraint mode and free mode is proposed since optmization only based on contraint mode will bring independence of constraint areas.A lightweighted front frame is achieved after the optimization.At last,free mode test amd MIMO test is conducted to verify the optimization and analysis.4.Optimization of truss size based on dynamics requirments is proceeded.According to the theory of random vibration,this paper achieves a conclusion-partical stiffness increase will lead to decreas of response of random vibration.Based on the conclusion,a multi-objective optimization which aims at reducing the random vibration response of the mirror mounting points is promoted.By detailed test of the truss propotype,reasonability of the truss design and theory promoted in this paper is proven.5.Design of thermal compensated truss structure is proposed.According to the principle that truss rod changes the same in axial direction and optical tolerance requirements,the author calculates the function between thermal coefficients of expansion of different truss rods and their value ranges.Thanks to the designability of thermal coefficients of expansion of carbon fiber,lay-up of carbon fiber which is used to fabricate the truss rod is achieved and can satisfy the stiffness demond.