concept of the electric propulsion and the result of the mission analysis to propel the 10 MW model from a low Earth orbit to a geosynchronous orbit. He concluded that MPD arcjet which is being developed by ISAS and industries would be the best propulsion system from the viewpoint of performance and of development effort, compared with other systems. Mr. Tsutsui, Nissan Motor Co., Ltd, proposed an unmanned CARGO-X space transportations system to supply construction materials for the SPS in cooperation with U.S. Space Shuttle. A unique feature of this vehicle is that every component of the vehicle will be recovered for the next operation or used as structure elements for the SPS. The liftoff weight of the vehicle is 960 ton and the payload is 30 ton in a low Earth orbit plus four 6-ton structure units for SPS made of the empty propellant tank. Prof. Nagatomo, ISAS, concluding the presentations of the study groups, talked about an idea of the overall operation procedure and the orbital constraints for power transmission tests in a low Earth orbit. It was supposed that the period for operation is three and one half years from the start of construction and to the end of the final power transmission test. A preliminary analysis to determine the test configuration for microwave transmission from a low Earth orbit to a ground receiving site was made with consideration of the actual geographical locations. Dr. Hashimoto, Central Research Institute of Electric Power Industry (CRIEPI), and Prof. Itoh, Hokkaido University were commentators for the session. Dr. Hashimoto recognized the importance of SPS study in Japan and surveyed various problems, technological as well as environmental. Based on a research made at CRIEPI, he concluded that SPS would come into operation around 2020 to supply electrical power in parallel with other power systems. Comment by Prof. Itoh supplemented the study area concerning the microwave receiving system which had not been treated in the 10 MW SPS study. He suggested the possibility of using a circular microstrip antenna (CMSA) for the ground microwave receiving system and presented the experimental result of power receiving characteristics of a CMSA matching at various frequencies. Although the symposium is not very formal and any interested person can participate, all the presentations were made in Japanese. For convenience of the oversea's researchers, the proceedings are published in English. A reader who wants to know more details of the presented papers, can receive the proceeding of the symposium free from the reporter who holds a limited number of extra copies.
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