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.

With the continuous improvement of the imaging quality requirement of the space optical system, the large-aperture mirror becomes the research focus. However, the increase of the aperture will increase the whole weight which results in high launch cost and degrades the mirror surface figure accuracy. Therefore, the lightweight design method of the mirror structure is of great importance. In recent years, many space telescope system schemes have demonstrated the progress of the structural lightweight design of mirrors, such as Spitzer, SOFIA, JWST, etc. This article reviews the main content and innovations of the research on the structural designs of mirrors including conventional machining designs and topology optimization structures. Meanwhile, some emerging designs (e.g., lattices and Voronoi structures) considering additive manufacturing (AM) are also introduced. Several key elements of different structural design approaches for lightweight mirrors are discussed and compared, such as material, lightweight ratio, design methods, surface figure, etc. Finally, future challenges, trends, and prospects of lightweight design for mirrors are discussed. This article provides a reference for further related research and engineering applications.

As space resources become increasingly constrained, the major space-faring nations are establishing large space target monitoring systems. There is a demand for both the number and the detection capability of space-based optical monitoring equipment. The detection range (i.e., field of view) and parasitic capability (lightweight and small size) of a single optical payload will largely reduce the scale and cost of the monitoring system. Therefore, in this paper, the optic-mechanical system of an ultra-lightweight and ultra-compact space camera and the optical alignment method are investigated around a fully freeform off-axis triple-reversal large field of view (FOV) optical system. The optic-mechanical system optimisation design is completed by adopting the optic-mechanical integration analysis method, and the weight of the whole camera is less than 10 kg. In addition, to address the mounting problems caused by the special characteristics of the freeform surface optical system, a dual CGH coreference alignment method is innovatively proposed. The feasibility of the method is verified by the mounting and testing test, and the test results show that the system wavefront difference is better than 1/10 λ. The imaging test of the space camera and the magnitude test results meet the design requirements of the optical system. The optic-mechanical system design method and alignment method proposed in this paper are instructive for the design and engineering of large field of view full freeform optical loads.

Flexure hinges have been widely used in space-borne telescopes for mounting reflective optics with high surface figure requirements. To realize the three-point flexural mount of a Φ750 mm primary mirror, a Cartwheel biaxial flexural hinge composed by filleted short beams is proposed and the dimensionless design graph method for the flexural hinge is presented. The finite element analysis is performed on the flexure model to validate the proposed method. We also demonstrate the feasibility of the proposed method experimentally. The maximum relative error of the rotational stiffness between analysis, testing result, and design value is 5.0%. The proposed dimensionless design graph can be used as a design tool to determine the optimal geometry of a spatial flexure hinge rapidly.

In this paper, the biaxial flexural mount is presented according to the requirements of the large aspect ratio mirror of an off-axis three-mirror anastigmatic (TMA) space-borne telescope, and the process of the optimal design of the flexural mount structure is discussed in detail. From the perspective of mechanics-based design of space-borne mirror assembly structure and integrated optical-mechanical analysis, the optimal axial mounting position, the optimal mounting angle and the optimal structural critical dimensions of the flexure hinge were determined to improve the surface shape accuracy. Finally, the mechanical vibration test further proved the rationality of the structure design and the accuracy of the simulation analysis. The flexural mount proposed in this paper is can be applied to other reflective optics with high surface figure requirements. The optimization method proposed in this paper can also be applied to the optimization of other forms of flexural mount.