Design of a long-focus unobscured reflective system for CubeSats based on freeform surfaces without planar symmetry and optical-digital joint optimization

CubeSats are becoming increasingly popular in scientific missions due to lower costs, but installing a long-focus unobscured reflective optical system within such a small volume is not easy. This paper proposes two methods to increase the focal length of optical systems in cube satellites. One method breaks the planar symmetry of the traditional off-axis three-mirror system, modifying the system structure to be off-axis in two directions, and simultaneously uses a fifth-order X Y polynomial freeform surface to correct the higher-order aberrations caused by the off-axis configuration. The other method utilizes convolutional neural networks to restore blurry images generated by high-specification, low-quality systems, while performing optical-digital joint optimization to improve system performance without sacrificing the output image quality. Design examples validate the feasibility of the proposed methods.