A HORIZONTAL-AXIS SPACEBORNE PRIMARYMIRROR DESIGN

Abstract The purpose of mounting a mirror is to maintain the correct position and control the deformation of the optical surface from external disturbance to allowable level. It is more difficult to mount a spaceborne large mirror in optical axis horizontal state than in vertical state on ground due to gravity. The design of a 1030 mm-diameterspaceborne primary mirror that is tested and aligned in laboratory with optical axis in horizontal state is described in this paper. A new kinematic mounting that is called three-spherical-joints mounting is proposed. Based on this new mounting concept, the primary mirror is lightweighted with Zerodur and ULE separately.ULE is selected finally as the material of primary mirror for it can be fabricated into sandwich structure which is the ideal structure for bending stiffness. The mass of lightweighted primary mirror is 50.5 kg. The detail mounting structure is described. This type of support offers the advantages of simple structure, ability of disturbance isolated and high natural frequency. Error budgets of surface figure are listed according to the developing processes. The primary mirror surface figure RMS error induced by environment disturbances are simulated. An aluminum dummy mirror assembly is made. Experiments show that the primary mirror has required static and dynamic performances which comply with simulations very well.