technologies. This approach can not be applied for a power system which can not enjoy the value added economy. The only way to reduce the cost is to reduce the cost of the orbital and ground facilities. One definite cost target of the orbital system of SPS 2000 is terrestrial solar power systems. Assuming the cost is 10 US$/W, the approximate figure for 10 MW model is 100 M USS. In this case, the launch cost dominates the payload cost, so that future reduction of the transportation cost will directly enhance the merit of the SPS system. In other words, success of the first SPS will benefit the future of space transportation in return. Public acceptance The radiation hazard caused by the transmitting microwave is a major public concern about SPS. The hazard is not known well but exaggerated and often misunderstood. A low power model like SPS 2000 would be comparable with a conventional radar system in terms of the radio power level. A rough estimation of the power level is given for SPS 2000 here. When the diameter of the transmitting antenna is 100 m and its distance from a rectenna is 1100 km. the rectenna diameter is 3 km. The radiation hazard of microwave of SPS 2000 which generate 10 MW will be roughly evaluated by comparison with the 5 GW Reference System having a 10 km diameter rectenna: the microwave power density for SPS 2000 is calculated to be forty five times smaller than that of the Reference System. The actual power level is about 0.5 mW per square centimeter at the beam center reaching to a rectenna.. Considering also the exposure time of a few minutes in an orbital period of about 100 minutes, the hazard can be evaluated in advance by accelerated experiments. Therefore, the radiation hazard will not be a major obstacle to the start of this project. On-site experiments on hazards evaluation can therefore be conducted safely, and experimental data will be obtained for later projects. International feature An SPS to be placed in a low earth orbit inevitably provides many nations with an opportunity to participate in the project, while an SPS in the geostationary orbit can be used exclusively by the owner country. Especially, in the case of SPS 2000, the benefits of the SPS system can be shared by the countries located in the equatorial zone. Thus the project can be planned in the context of international cooperation between industrialized and developing nations. The international community has the opportunity to do something constructive for the future, based on the technologies developed in the twentieth century, which were mostly used for military purposes. SPS 2000 is not large enough for such a purpose but may work as the initiator of this kind of cooperative enterprise. Conclusions ISAS solar power satellite working group has developed a preliminary concept of a 10 MW class SPS strawman model. In terms of the principle and key technologies, the model is in accordance with the Glaser's original concept and the Reference System of the CDEP. However, the size and the purpose are different from theirs, since the study aims at demonstration of electric power supply to customers at earliest opportunity,
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