Research On Ground–based Large-aperture Telescope Mount And Thermal Control For Primary Mirror

Large aperture optical telescope is a photoelectric detection instrument that widely used in astronomical observation,laser communication,et al.With the improvement of the system space resolution requirements,the aperture of the telescope becomes larger and larger.Good pointing reproducibility and image quality are the necessary conditions for the operation of modern large aperture telescope.In recent decades,many new technologies have been developed in the telescopes,including optics,dynamics,computers,automatic control and precision machinery,which has broken through the limitation of the mirror aperture of the telescope,reduced the cost,simplified the telescope structure,and maked the telescope manufacturing technology develop rapidly.Based on defferent applications,key technologies of the telescope is defferent.Then,the key technology will be optimized.In order to meet the pointing and image quality requirements of the telescope,this paper adopts the technical route of theoretical deduction,structure design,simulation and experimental verification of large-aperture telescope.Meanwhile,based on application of telescope,the paper take a deep research on the the telescope mount and the primary mirror.In particular,the main contents and concrete results of the paper are as follows.1.The development of telescopes is introduced,including in the high stiffness structure and active optics.The influence of the primary mirror thermal environment on the image quality is illustrated.The active thermal control of the primary mirror for large aperture telescopes is summarized.Both the temperature gradient within the primary mirror and the temperature defference between mirror and ambient air are must controlled in order to match the image quality.2.The research on mount structure baesd on roller bearing consists of pointing error,bearing and large-scale instruments.Taking a meters class aperture telescope as the research object,the structure form of telescope mount is briefly introduced,and the key technology of the mount structure are analyzed.According to the application requirement,the high angular ball bearing,integral with a radial ball bearing and a pair of cylindrical roller bearing are selected to be mounted at azimuth and elevation shafting,respectively.The topology optimization theory is selected to analysis the key large-scale instruments of the telescope,getting the main load path.The key large-scale instruments are lightweight designed,and then the finite element analysis of statics and modal of each instrument is carried out respectively,whose stiffness can totally match the requirements.3.The mount system is analyzed in statics and modal.Then the modal test is carried out to verify the system design and the simulation.The deformation and strain results under gravity meet the requirements of static capacity,ensuring the stability of main optical elements.Meanwhile,the low-order modal frequency and shape results can keep against wind load and earthquake.Then,the mode test on the telescope is carried out through the LMS system at a certain platform.The test results are consistent with the simulation results,which verify the rationality of the structure design and the correctness of the finite element simulation,and provide guidance for the telescope design.4.The primary mirror thermal control system is optimized analyzed.The geometry and the thermal environment of the primary mirror of the telescope are introduced.A lightweighted mirror is equivalent to a thin mirror without ribs in the thermal analysis to analytically calculate the temperature field of the primary mirror in the early design of the large-aperture telescope.The primary mirror at natural convection is simulated and analyzed.The optical surface deformation cannot meet the requirements of telescope observation.Based on the surface requirement,an air-knife thermal control system at optical surface is designed and optimized,which can help to form a uniform flow field on the thermal boundary layer and remove the residual heat on the optical surface,meeting the observation demand.5.A prototype experiment of thermal control system is carried out to validate the feasibility of air-knife thermal control system for large-aperture primary mirror.The subscale mirror is a ?630 mm fused silica lightweighted one.The experiment is carried out in a hermetic thermo-cycling experiment room with different environmental conditions.The results have a significant effect on the thermal control system for large-aperture primary mirror.The scaling principle can be applied in other research of the telescope.