Optical system of aplanatic telescope with a 100 m spherical primary mirror

We propose an optical system of an extremely large telescope for ground-based or planetary use. The system comprises a segmented spherical mirror with a diameter of 100 m and f-number of f / 1. There are three annular zones on the primary mirror, which corresponds to three annular telescopes (ATs) with f-numbers f / 2, f / 3.2, and f / 5.2, all using a concave cardioidal secondary mirror with a maximum diameter of 3.18 m. This two-mirror system satisfies Fermat's principle and the Abbe's sine condition. The central zone of the primary mirror with a diameter of 23.8 m is used for the central three-mirror telescope, which is based on an afocal two-mirror system with a convex aspheric secondary mirror with a diameter of 3 m. Four possible configurations are presented for the central telescope, which makes it possible to vary the f-number in a wide range with design examples given for f / 1, f / 4.2, f / 14, and f / 33 systems. The ATs form three coherent images of the same astronomical object, which offers possibilities of simultaneous observations at three different wavelengths or image processing of a combined image with enhanced angular resolution. The main goal of the paper is to investigate the properties of new optical systems for ground-based and space telescopes with a fast spherical primary mirror for which aberration correction is achieved with a minimum number of auxiliary aspheric mirrors near the prime focus.