Satellite-to-Ground Optical Communication System on Low Earth Orbit Micro-satellite RISESAT

Within the scope of a Japanese FIRST (Funding Program for World-Leading Innovative R&D on Science and Technology) program led by Professor Nakasuka of University of Tokyo, Tohoku University is developing a 50kg-class international scientific microsatellite named RISESAT. In addition to various scientific instruments, RISESAT is also equipped with a laser communication terminal VSOTA, developed by Japanese National Institute of Information and Communications Technology (NICT). Tohoku University and NICT are now developing the engineering model of the satellite and undertaking its ground tests. VSOTA has two different wavelengths of laser outputs in 980 nm and 1540nm. The collimators for these are fixed with the satellite structure pointing toward the Earth direction. RISESAT aims to control the direction of the laser beams being precisely pointed toward the NICT's optical ground station with a pointing accuracy of better than 0.4 deg (3 sigma) during the fly-by. RISESAT can send actual scientific data obtained by payload instruments through this optical communication link. This will be the world first demonstration of microsatellite-to-ground optical downlink. This will bring innovation to misrosatellite's system engineering, utilization, and communication network. This paper describes the detailed specification, system design strategy, and real-life implementation of laser communication system on the micro-satellite RISESAT.