Research On The Main Optomechanical System Of Balloon Borne Telescope In Near Space

Near space telescope observation has broad application prospects in the field of military strategy and scientific observation.The mechanical and thermal stability of its main optomechanical system affects the imaging quality of the telescope and is a key link.During the flight and observation of the near space telescope,the main optome-chanical system will be affected by a series of severe mechanical environments such as gravity,temperature,acceleration,and impact and so on.It is of great significance to study of the main optoechanical system of the high mechanical-thermal stability for imaging quality.Aiming at the problems of the lightweight and decoupling of primary mirror as-sembly,the fast optimization of secondary mirror assembly,this paper carries out the research about the aspects of index allocation,optimization design,automatic link sim-ulation analysis,experimental verification,and realize the first attempt of near-space planetary scientific observation in China.The main research contents of this paper are listed as follows:Firstly,the successful balloon borne telescopes at home and abroad have been in-vestigated to provide reference and deepen understanding for the development of such payloads in China.Combined with the processing and assembly tolerance of optical de-sign,the index distribution of each sub component of the main optomechanical system is completed,which provides a basis for the optimal design of subsequent components.Secondly,the primary mirror has been optimal designed combined with topology optimization and compromise programming method,the weighted compliance under the four observation angles has been taken as objective function to optimize the initial primary mirror structure topologically,and a basis for grouping of lightweight ribs has been obtained.The lightweight ribs have been divided into two different groups.Due to the large number of variables,the design of experiments has been carried out.The parametric design has been based on the compromise programming method,which has converted contradictory multi-objectives into single-objectives.After parameterization,the mass of the816mm Si C mirror is only 28.5kg,which is 15.7%lower than the initial structure,and the lightweight rate achieves 79.5%.By establishing the surface shape accuracy change and the force on the support position,the compound support design is separated,and the support structure is optimized by combining the index distribution and decoupling.The primary mirror component performed well in the surface shape accuracy,stability,mechanics and decoupling.Thirdly,the fast optimization design of the secondary mirror assembly based on mesh deformation is adopted,and the mesh deformation has been written into the in-put script of Hypermesh through Tcl language to change the size parameters and axial installation position of the flexure.Compared with the parametric link,the process of parametric modeling and remeshing can be omitted,the fast optimization method based on mesh deformation can reduce the single optimization time from 10min to 40s,which can effectively improve the efficiency.The optimization results of secondary mirror assembly meet the index requirements,and the design cycle is effectively shortened.Then,after achieving the optimal design of the primary mirror assembly and the secondary mirror assembly,the truss structure has been selected for the main support structure through comparative analysis,which has certain advantages in terms of mass,radial displacement and first-order frequency.The truss adopts the mature Serrurier truss structure,and the thermal expansion coefficient of the truss rod is optimized to-2×10^-6/^°C.After simulation analysis,the truss structure with primary and secondary mirrors meets the design requirements in terms of mechanical and thermal stability.Finally,a series of processes from processing,manufacturing,and assembly of the primary mirror assembly are described in detail,and the surface shape error and me-chanical test of the primary mirror assembly and the secondary mirror assembly are carried out.The surface shape is better than/50,and the error between the experi-mental results and the simulation analysis is within 2%.The truss has also completed its corresponding mechanical test and stability test,and the error of its mechanics with the simulation is also within 3%,the stability meets 10″index requirement.The static and dynamic simulation analysis of the main optomechanical system is carried out,and its performance meets the observation requirements.The test of the telescope system shows that its average wave aberration in five fields of view is 0.06974,which is better than/14.The telescope has been hoisted and observed in the field to verify the good its performance.The related results of this thesis provide some reference for the near space telescope.