Optical design of a Ritchey–Chrétien telescope with a decentered square aperture for 3U CubeSat

This study presents the optical design and performance evaluation of a Ritchey–Chrétien telescope with a two-element corrector, developed for high-resolution Earth-observation imaging on a 3U CubeSat. The system utilizes a reflective configuration with a square 80mm × 80mm primary mirror (M1), and an effective focal length of 900mm. The corrector compensates for optical aberrations, enabling near–diffraction-limited performance across the field of view. At an operational altitude of 500km, the telescope achieves a ground sampling distance (GSD) below 5m and a swath width of 7.4km × 7.4km, corresponding to a full field of view of 0.84° × 0.84°. The design maintains a modulation transfer function (MTF) exceeding 0.20 at the Nyquist frequency, corresponding to a detector pixel size of 6.5µm. A comprehensive tolerance analysis has been conducted, addressing manufacturability, alignment sensitivity, and structural stability.