Optimal design of a Φ760 mm lightweight SiC mirror and the flexural mount for a space telescope

Abstract

A flexural support technique for lightweighted Primary Mirror Assembly (PMA) of a space telescope is presented in this article. The proposed three-point flexural mount based on a cartwheel flexure can maintain the surface figure of the PMA in a horizontal optical testing layout. The on-orbit surface error of the PMA causes significant degradation in image quality. On-ground optical testing cannot determine the zero-gravity figure of the PMA due to surface distortion by gravity. We unveiled the crucial fact that through a delicate mounting structure design, the surface figure can remain constant precisely without inducing distinguishable astigmatism when PMA rotates with respect to the optical axis, and the figure can be considered as the zero-gravity surface figure on the orbit. A design case is described to show the lightweight design of a SiC mirror and the optimal flexural mounting. Topology optimization and integrated opto-mechanical analysis using the finite element method are utilized in the design process. The Primary Mirror and mounting structures were fabricated and assembled. After the PMA mirror surface was polished to λ/50 RMS, optical testing in different clocking configurations was performed, respectively, through rotating the PMA by multiple angles. Test results show that the surface figure remained invariant, indicating that gravity release on the orbit will not cause an additional surface error. Vibration tests including sweep sine and random vibration were also performed to validate the mechanical design. The requirements for the mounting technique in space were qualified.

Lightweight Design of Multi-Objective Topology for a Large-Aperture Space Mirror

“…The initial design based on topology optimization is shown in Figure 6a. Although topology optimization has led us to obtain a conceptual optimal design, it could not be implemented in engineering directly because of the unequal quilting effects caused by the unevenly distributed ribs during mirror fabrication [13]. According to the relative densities, the elements retained in the topology optimization result are divided into three types of ribs, as shown in Figure 5.…”

Optimization Design of Large-Aperture Primary Mirror for a Space Remote Camera

“…Qin Tao et al used a hybrid IPSO-IAGA-BPNN algorithm to optimize the structural parameters of the reflector, and the advantages and disadvantages of different optimization methods are also analyzed [ 10 ]. Zongxuan Li et al studied the silicon carbide primary mirror of a space telescope with the semi-enclosed triangular lightweight form at the back and three-point support method at the back, optimized the design and fabricated the primary mirror with a diameter Φ760 mm and flexible hinge, and the surface shape accuracy reached 0.02 λ [ 11 ]. Hagyong Kihm et al used a multi-objective genetic algorithm to optimize the ZERODUR ® primary mirror and a new bipod flexure, which met the design objectives [ 12 ].…”

Bayesian Regularization Algorithm Based Recurrent Neural Network Method and NSGA-II for the Optimal Design of the Reflector

“…Liu et al used topology optimization and parameter optimization to optimize the mirror surface deformation and weight of the reflection [5]. Li used topology optimization and integration analysis for the lightweight design and mounting of a 760 mm diameter SiC reflector [6]. In addition to the above-mentioned topology optimization methods, intelligent algorithms and surrogate models have been applied to the optimal design of mechanical structures in recent years [7][8][9][10][11][12].…”