The optimization of segment's axial support point for large astronomical telescopes

Existing axial support for segments mostly adopts the Whiffletree support mode. The location of the support point will have a great influence on the surface precision of the primary mirror, and then influence the final imaging quality of the telescope. At present, there is no special support technology for traditional and thin mirror. In this paper, the research is based on LOT's hexagonal segment (the surface is hyperboloid, diagonal line is 1.2m, thickness is 45mm, material is Zerodur), which is designed by Huazhong university of science and technology. The optimization of the Whiffletree axial support point of the segment is carried out. Efficient optimization algorithm is used in the research. After building parameterized model of segment support point location, FEM is used to obtain segment surface deformation. Taking the minimum RMS of deformation on segment surface under gravity as the goal, optimized software ISIGHT is applied to find the best support point location. Zernike orthonormal polynomials for hexagonal pupils is used to remove rigid-body motion. Finally, the best support point location point is obtained, the RMS of the segment surface deformation is 11.56nm and the PV is 63.98nm. The result can meets the requirement of LOT design well.