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The Rapid International Scientific Experiment Satellite (RISESAT) is a 50-kg-class Earth observation microsatellite that is currently being developed at the Space Robotics Laboratory (SRL) of Tohoku University, with a planned launch data in 2018. Intended to demonstrate a cost-effective and reliable microsatellite bus system, RISESAT features various scientific payload instruments from institutions and organizations around the world. Among the payloads are the Very Small Optical Transponder (VSOTA), a compact, dual-band (980 nm, 1550 nm), lightweight laser signal transmitter developed by the Japanese National Institute for Information and Communications Technology (NICT), and the High Precision Telescope (HPT), a multi-spectral, high-resolution Cassegrain telescope developed by Hokkaido University and intended for Earth and astronomical observations. Using these two payloads, RISESAT can demonstrate satellite-toground one-way laser communication. This experiment is intended to demonstrate optical communication capability within the scope of the available hardware resources on a microsatellite dedicated to numerous other scientific endeavors. Hence, VSOTA is lighter, less power intensive, and more simplified than other optical transmitter terminals. Internal gimbal mechanisms for fine pointing have also been eliminated, thus the tracking of the optical ground stations will be achieved using body pointing of the satellite. Recently, end-to-end electrical configuration and communication tests have been conducted for both the engineering model (EM) and the flight model (FM) of the VSOTA assembly. This paper provides an overview of VSOTA and its space-to-ground optical communication demonstration, and describes the current status of the RISESAT optical communication subsystem assembly and integration.
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