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The solar power satellite (SPS) and space solar power system (SSPS) have been studied for years as future alternative energy sources when fossil fuel becomes scarce. The SPS is a satellite in orbit that collects solar energy and transmits the energy to various destinations. SSPS is a total system that includes SPS and ground facilities to utilize power from the SPS. JAXA is presently conducting system-level studies of a microwave-based SSPS (M-SSPS) and laser-based SSPS (L-SSPS). The M-SSPS is comprised of solar energy collection mirrors, power generators (PV arrays), and power transmitters (amplifiers and antennas). The diameter of the primary mirror will be a few kilometres and the total mass will be 10 thousand tons. The electrical power received on Earth from this satellite may be 1 GW. The laser-based SSPS (L-SSPS) uses a laser to transmit power. The laser beam will be generated directly from concentrated solar light using a laser medium. SSPSs have been previously studied as tools to supply energy to Earth. Recent interest in lunar and planetary exploration has drawn attention to the use of SSPSs, since lunar exploration is currently focused on the polar region of the Moon, where little sunlight is available. The SSPS can also be used to provide energy to rovers, robots, and other systems working on the lunar or planetary surface.