Design Optimization Method for Additive Manufacturing of the Primary Mirror of a Large-Aperture Space Telescope

The lightweight design of the sandwich mirror, as a commonly used space primary mirror structure, is one of the key topics for the design of space-based optomechanical systems. Owing to the limitation of traditional manufacturing capabilities, the induced holes on the mirror back are usually of the open or half-open form, which compresses the optimization design space. With rapid development of additive manufacturing (AM) technologies, it is possible to fabricate a closed-back sandwich mirror with a complex internal structure to achieve outstanding performance. In this paper, a novel topology optimization model for a closed-back primary mirror of a large-aperture space telescope is proposed. First, extrusion constraints are considered in the optimization model to obtain the layout design of stiffening webs inside the mirror core. Then, a simply connected constraint, as one type of constraint in AM, is considered to avoid enclosed voids in the structures. Through solving the proposed model, a new closed-back sandwich mirror configuration with nonclosed treelike vertical stiffening webs, is achieved. In addition, the thicknesses of the internal stiffening webs are optimized for minimizing the weight with the constraint of the surface shape error of the mirror face. Compared with the classical and existing sandwich mirror configurations, the optimized mirror has significant superiorities on optical performance and the lightweight ratio, which illustrates the effectiveness of the presented method. The method is a prospective study in the design of a space mirror fabricated using AM. (C) 2016 American Society of Civil Engineers.