A feasibility study was conducted for an optical imager system assumed to be mounted on a geostationary orbit satellite for Earth observation. The targeted spatial resolution was less than 10 meters for panchromatic mode at nadir observation conditions, and the observation area was assumed to 100 × 100 square kilometers. The optical system was designed based on a Korsch three mirror anastigmat; the primary mirror was 3.5 meters in diameter, and the focal length was approximately 45 meters. The worst wavefront error was estimated at less than 0.017 λrms in the field of view. As the next step, the primary mirror was segmented, and a trade-off study was conducted on two types of segmented mirror configurations. The optical performance of each configuration was compared in terms of PSF and MTF. Moreover, the deterioration of optical performance due to the misalignment and distortion of the segmented mirror was discussed and numerically estimated by using the Monte Carlo method. The sensitivity of the wavefront error was consequently estimated for the segmented mirror assembly.
Optical mirrors for space telescopes, which require high precision and high thermal stability, have commonly
been made of glass materials such as ultra low expansion glass (e.g. ULE®) or extremely low expansion glassceramic
(e.g. ZERODUR® or CLEARCERAM®). These materials have been well-known for their reliability
due to their long history of achievements in many space applications.