Design of an All-Spherical Catadioptric Telescope with Long Focal Length for High-Resolution CubeSat

Abstract

Telescopes with aspherical mirrors, long focal length, and large aperture are usually used to acquire high spatial resolution remote sensing images of earth surface, while they are expensive and large in volume. CubeSat is one of the fastest growing sectors in space science and technology, for that it has a relative superiority over other micro and mini satellites in terms of their shorter manufacture time, lower complexity, and most importantly less cost. An optical design of an all-spherical catadioptric telescopic objective for 3 U CubeSat missions is proposed in this chapter, aiming at implementing as low cost as possible. In order to correct aberrations of an all-spherical system, two corrector groups are introduced. One is afocal lens group at the front end of the primary mirror to eliminate spherical and coma aberrations of two-mirror objective. It is composed of two lenses with opposite focal power for achromatic design. Its diameter is close to the size of the primary mirror. The other is a negative focal power group with four pieces of lenses before image plane that amplifies the focal length of the two-mirror structure and corrects astigmatism, field curvature, and distortion aberrations of the whole system. All lenses used are made from the same kind of glass material for the convenience of the athermalization design. Furthermore, in order to minimize its outer barrel length, the secondary mirror adopts a Mangin type, which greatly reduces the marginal ray height of full field of view. Based on the mentioned basic idea and structure, its primary aberration formulas are derived, and the methods for the correction of its aberrations are analyzed. Then a designed example is given. It approaches diffraction-limited imaging performance. The total length of the system is 1/6 less than its effective focal length. At last, tolerance analysis is performed for verifying its manufacturability.