Experimental study of 3.6-meter segmented-aperture telescope for geostationary Earth observation satellite

The imager that observes the ground surface with high spatial resolution from geostationary orbit has been studied. To obtain image data with high ground sampling distance (GSD) from a geostationary orbit, an extremely large-diameter and long-focal-length telescope is required. In order to realize this imager, we plan to adopt a synthetic aperture type reflection optical telescope (Korsch type) in which the primary mirror is composed of six segmented mirrors. The diameter of the synthesized aperture telescope is approximately 3.6m, and the focal length is approximately 30 m. Prior to the development of the actual imager, we have been producing a full-scale prototype of the segmented mirror that constitutes the primary mirror and its supporting structure. The aperture shape of the prototype segmented mirror is hexagonal, and its diagonal length is approximately 1.35 m. The supporting structure of the prototype segmented mirror incorporates a mechanism (6-axes adjustment mechanism) for adjusting the alignment of the segmented mirror with six degrees of freedom. A mechanism for adjusting the curvature of the segmented mirror (curvature adjustment mechanism) was also incorporated. In this paper, the design, the manufacturing, and the testing status of this prototype are described.