Research On CFRP Truss Support Technology Of Lightweight Space Camera

With the continuous development of the aerospace industry,remote sensing technologies have been widely used in all walks of life in the national economy.Space-to-ground observation is an important means to obtain ground information.The basic method is to use space remote sensing camera to image the ground to obtain clear and intuitive image information.At the same time,the spatial resolution of the space remote sensing camera has also evolved from the previous tens of meters and several meters to the current sub-meter precision,therefore more stringent requirements are put forward on the various indicators of space cameras.The camera is subject to complex mechanical environments?shocks,vibrations,overloads,etc.?during launch,and truss?the truss described herein is the support structure between primary and secondary mirrors?is the support structure between the main optical components of space camera,so it must has good strength,stiffness and structural stability to ensure the positional relationship between the optical components and the image quality of camera.Compared with traditional metal materials,carbon fibre reinforced plastics?CFRP?has physical and mechanical properties such as low density,high specific strength,high specific stiffness and good thermal stability,therefore CFRP structural components are widely used in space remote sensors.This paper is aimed at the specific requirements of a commercial satellite optical payload?total mass of camera less than 25kg,gaze video or push-scan imaging mode,R-C optical system with correction mirror,ground object resolution better than 0.9m,imaging width greater than 22.5km?,CFRP truss support technologies of lightweight space camera are researched in depth:Compared the structure types of truss,and the simple three-bar truss structure is selected.Based on the Optistruct solver,the maximum natural frequency of truss as the optimization goal,angle optimization,topology optimization?SIMP,Solid Isotropic Material with Penalization Model?and size optimization?Free Shape Technology?design of truss are done to obtain the good truss support structure.According to the optimized design results,combined with the processing technologies of metal structural parts and composite structural parts,the truss structure is designed in detail,to obtain the truss design scheme meeting the index requirements.The maximum outer diameter of the truss is?430mm,the height is 476mm,and the total mass is less than 2.2kg.The angle between the truss rod and the truss axis is 16.3°,and the diameter ratio of the secondary mirror chamber and the support ring is 1:2.9.The truss rod has a cross-shaped cross section,the support ring has a concave cross section,and nine reinforcing ribs are arranged symmetrically on the circumference of the support ring.The direction of the laminate,the order of placement,and the number of layers,need to consider the external environments?force,thermal load,etc.?,to design layers of the structural part according to the specific conditions.The classical laminate theory and its application in the design of composite structural parts are introduced.Based on Optistruct solver,the optimal design of the truss rod and the support ring are carried out with the maximum natural frequency as the optimization target,to obtain optimal layup of the truss rod is[±12°]₇0°and the optimal layup of the support ring is[0°/90°/45°/-45°/0°]₆.Finally,it is determined that the truss rod and the support ring are all formed by a press forming process.In order to investigate the strength,stiffness and thermal stability of the truss,based on the finite element analysis software such as Hypermesh/Patran/Nastran,the virtual tests of the truss are carried out.The static analysis shows that the self-weight deformation of the truss and the deformation subjected to the gravity of secondary mirror assembly are better than 4.21??,meeting the accuracy requirement of 10??,and it has good stiffness characteristics.The dynamics analysis shows that the first-order fundamental frequency of the truss is 181.2Hz,which is significantly higher than100Hz,and it can effectively avoid the resonance phenomenon of the truss during the launching process,and the acceleration responses of sinusoidal analysis and random analysis are reasonable,indicating that the truss has good strength,dynamic stiffness indicators.The temperature rise analysis shows that the deformation of the flexible support of secondary mirror is less than 3.16?m,so the relative positional relationship between the primary and secondary mirrors of the space camera can be well guaranteed,and to guarantee camera image quality.The statics,dynamics and structural stability tests of the truss are studied.The static tests show that the self-weight deformation of the truss assembly is between0.90???4.32??,the average value is 2.28??,and the truss deformation subjected to the gravity of secondary mirror assembly is between 1.26???5.40??,the average value is3.37??,which is slightly higher than the self-weight deformation of the truss component,basically consistent with the static analysis result of virtual tests?2.57??,3.53???,indicating that the truss structure is reasonable and has good stiffness characteristics.The dynamics tests show that the fundamental frequencies of the truss in the three directions of X,Y and Z are 179.9Hz,179.9Hz and 598.3Hz,which are basically consistent with the dynamics analysis results of virtual tests?181.2Hz,181.2Hz,638.0Hz?,and the errors are 0.7%,0.7%,and 6.6%,which can effectively avoid resonance phenomena,and the acceleration responses of sinusoidal vibration and random vibration are reasonable,indicating that the truss has good strength,dynamic stiffness indicators,to withstand the effects of complex mechanical environments experienced by space camera during launch.At the same time,before and after the vibration tests,the deformation of the truss subjected to the gravity of secondary mirror assembly are measured,and the variations of horizontal angle and pitch angle are less than 3.99??,indicating that the truss has good structural stability and can guarantee the relative position between the primary and secondary mirrors,and the imaging quality of space camera.The total mass of the truss assembly by actual machining is 2.14kg,which is1/3?1/2 times of the metal truss,and has good index properties such as strength,stiffness and structural stability,which can withstand the effects of complex mechanical environments experienced by space camera during launch,to ensure the positional relationship between the primary and secondary mirrors,and camera's imaging quality.It provides an important reference for the development of CFRP truss support technologies of lightweight space camera in China.