Abstract: A structural design scheme is proposed for the 400 mm aperture capture and tracking telescope. In this scheme, the main mirror is supported by three-point flexible bottom support and ball head spindle side support to avoid the interference of support stress and ensure that the main mirror has high profile accuracy. And an indium steel connecting rod structure is used in the connection of primary mirror and secondary mirror to ensure that the distance between primary and secondary mirrors changes within the tolerance range under large temperature difference, so that the telescope has good image quality under the limit conditions. Furthermore, the finite element model of the whole structure of the telescope is established, and the shape accuracy of the main mirror and the structural strength of the barrel are analyzed. The RMS value of the main mirror shape is better than 1 / 40λ, and the relative eccentricity and inclination of primary mirror and secondary mirror are 3μm and 2.5″ respectively, which meets the index requirements. Finally, the optical parameters of the telescope are measured quantitatively by using laser interferometer and collimator, and it is found that the root mean square (RMS) value of optical system is better than 1/14λ, the full width at half maxima (FWHM) value of star point is 2.3, which is close to the diffraction limit level. The designed scheme has certain reference value for the structure design of similar telescopes.

Key words: optical mechanical structure, main mirror support, diffraction limit, surface accuracy