Design Of High-precision Repeatable Secondary Mirror Deployment Mechanism For Space Camera

Under the background of the rapid development of commercial aerospace,microsatellites have gradually become a research hotspot in the field of aerospace remote sensing due to their low R&D cost,short development cycle,flexible application,small size,light weight,and mass production.However,its carrying capacity is limited,and the size and weight of the payload will be greatly limited,and satellite networking and co-flight can be carried out through multiple microsatellite platforms equipped with high-resolution space cameras,so as to achieve or exceed the same function as a single satellite of equal mass.For space cameras,high resolution requires a longer focal length of the camera,and long focal length leads to a larger distance between the primary mirror and the secondary lens,which leads to an increase in the volume of the space camera and low space utilization.In order to fully reduce the envelope size of space camera launch and reduce the launch cost of space camera,this paper designs a secondary mirror deployment structure based on space four-link for coaxial three-lens optical system.Firstly,this paper selects the appropriate optical system structure according to the comparison,assigns the tolerance of the whole system according to the results of the optical design,and determines the deployment accuracy requirements of the unfolding mechanism.Secondly,the moment of inertia and turning torque of the entire unfolding mechanism are calculated,and the required locking torque is calculated according to the requirements of the system.By selecting the appropriate drive motor according to the torque requirements,the drive form of the secondary mirror deployment mechanism is determined.According to the distribution of each component of the back plate of the primary mirror,the expansion direction of the secondary mirror deployment mechanism is determined,the secondary mirror deployment mechanism is simplified,the relationship between the compression ratio and the structural parameters is determined according to the state of the folding state,and the appropriate compression ratio is determined according to the actual engineering experience,so as to determine the structural parameters of this paper.The error source of the secondary mirror unfolding mechanism was analyzed,and the theoretical error of the secondary mirror unfolding mechanism was calculated according to the micro-displacement synthesis method.Then,the finite element analysis of the model of the secondary mirror unfolding structure was carried out,the stiffness of the secondary mirror unfolding mechanism in the working state was verified by static analysis,the unfolding mechanism was determined to meet the requirements of the microsatellite platform through modal analysis,and the influence of micro-vibration on the working state of the secondary mirror unfolding mechanism was verified according to the dynamic response analysis under sinusoidal excitation conditions.A structural repeatability test scheme is designed to verify the repeatability and accuracy of the secondary mirror unfolded structure.After the design of the secondary lens unfolded structure,the optical axis direction length of the space camera is compressed from 875 mm to 324 mm,the volume can be compressed by 63%,the fundamental frequency in the unfolded state is 96.64 Hz,the maximum limit error of repeated unfolding displacement is 15.61μm,and the maximum tilt limit error is 16.89".Finally,the work completed in this paper is summarized,the innovation points and shortcomings of this paper are pointed out,and the follow-up work is prospected.