(3) SPS 2000 Concept Study The working group proposed a concept study of a mode) SPS as a research area to coalesce the diverging activities of the subgroups. The model should be designed as a realistic SPS model in contrast to the gigantic U.S. Reference System. Because of its realistic configuration, it has been named "SPS 2000” (Fig. 8). The model has evolved from the previous two concepts of SPS with technical drawings of the general view in Japan. One is the 10 MW SPS, conceptualized by the Space Technology Committee of the Japan Machinery Federation in 1983 for a report on the future prospects of the space program, and the other is the Energy Storable Orbital Power Station (ESOPS), which was studied by ISAS and Toshiba. For the current study, it is assumed that the power level is 10 MW and the operating orbit is a low altitude equatorial orbit. To simplify the system, the model SPS has no energy storage, and the attitude will be stabilized by gravity-gradient. The critical technology is the transmitting antenna, which must control the direction of a narrow 2.45 MHz microwave beam over a scan angle of sixty degrees. This is belie ved to be possible only with a phased airay of densely distributed small antenna elements powered by semiconductors. The design work is under way. and the task team is calling on other organizations for participation in the voluntary study, on the base of no fund exchange. (4) Microwave Garden Project At present, microwaves of 2.45 GHz are being considered for use for power transmission from solar power satellites to ground, as assumed for the U.S. Reference System designed to supply 5 GW electricity on the ground. In that case, the maximum level of microwave power at the center of the rectenna is designed to be 23 mW/cm’, w hich is lower than the level of 100 mW/cm: that causes prominent thermal effects on living species. However, the non-thermal effects of microwave radiation on biological systems is unknown even at lower energy levels. This has been one of (lie most important research subjects for SPS. The major purpose of the .Microwave Garden project of the SPS Working Group is to investigate long lenn effects of micro- waves on biological and ecological systems. Microwave Garden has experiment and control areas (8m x 8m for each) (Fig. 9). The central part of the experiment area with 4m x 4m is irradiated by microwaves generated by two magnetrons each with output power of 720 W. Emissions are modulated by 100 Hz, because the microwave source is a commercial microwave oven. Differences of biological and ecological activities will be compared between the experiment and control areas. The result is expected to be useful in evaluating risks of energy transmission by microwaves. Fit;. 9 The Microwave Carden in ISAS S.rg.imih.ir.i campus Ftp, H Concept oi a 10MW solar power satellite: SPS 2000
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