Compact Korsch-type CubeSat telescope for optical remote sensing

In the paper, we proposed a compact Korsch-type CubeSat telescope for optical remote sensing validation. The optical payload will be mounted on a 6U CubeSat named ONGLISAT. This telescope has an aperture of 92 mm and an effective focal length of 725 mm, providing a field of view of 2.2 degrees. The optical payload is equipped with a linear TDI CMOS image sensor, capable of capturing high-resolution panchromatic images with a ground sampling distance (GSD) of 2.8 meters in a low-Earth orbit at an altitude of 406 kilometers. The Korsch telescope consists of three aspheric mirrors (primary, secondary, and tertiary mirrors) as well as a roof mirror. This paper presents details of the optical design, assembly, integration, and performance test for the compact Korsch telescope. The image quality of the Korsch telescope is evaluated by the contrast transfer function (CTF). Finally, after thermal vacuum cycling testing and vibration testing, the telescope still maintains a CTF of 0.12 at 50 lp/mm line pairs. The Korsch telescope has the characteristics of a low obstruction ratio and high stray light blocking. The design of the telescope has higher resolution, a smaller size, and lower launch costs, which are beneficial for future applications in science, agriculture, commerce, and disaster relief. Furthermore, its optical quality can be quickly validated, serving as a preliminary study for larger telescopes.