NewTrans3.txt[9/15/2024 8:36:13 PM] budget). This is to forget that a large number of space developments (NASA's space transportation system, assembly in orbit) or energy developments (solar cell programs) constitute technological research necessary for the realization of a CSS. Under these conditions, it can be estimated that current efforts in favor of these two energy technologies are comparable. Cost comparisons between the four energy systems mentioned are certainly very premature. The assessments made so far for the DOE and NASA have such a margin of uncertainty that no conclusion can be deduced from them. On the other hand, environmental problems can and must already be considered. We have cited two ecological obstacles that can limit the development of coal-fired power plants and breeder reactors. Thermonuclear fusion does not seem to be exempt from radioactivity problems. As for Space Solar Power Plants, it is clear that the microwave link raises two major questions: the long-term biological effects of low-intensity irradiation; and the large surface area required by the ground-based receiving antenna and the safety zone that will be defined around this antenna. The two questions are also linked: if a very low intensity of the microwave beam is required at the edge of the safety zone, the size of the latter will naturally be increased. These questions must be explored in depth quickly, and receive international interest. But in any case, we believe that the size of the reference system rectenna (100 km2 at mid-latitudes) is too large, and poorly adapted to the problems of populated energy-consuming regions in Europe, the United States and Japan in particular. Current technological thinking on CSS should probably focus primarily on ways to reduce the surface area on the ground required for a CSS. A final remark is necessary concerning space solar power plants: of the four systems considered, they are the only ones to use a truly renewable energy source, the Sun. In the very long term, this will certainly be a considerable advantage. In some studies, CSS are also considered in competition with other technologies for exploiting solar energy: terrestrial heliothermoelectric or photovoltaic power plants, decentralized photovoltaic generators in particular. This competition is not justified, because no other solar technology is on the horizon by the year 2000 capable of massively supplying basic electricity. From this point of view, CSS constitute a unique possibility for using solar energy, complementary to all other forms of its use (4). REFERENCES 1. Edison Electric Institute, World Economic Growth, in Economic Growth in the Future. Chap. 7, McGrawHill, New York. 2. World Energy Demand in 2000, Full report to the Conservation Commission of the World Energy Conference, IPC Science and Technology Presse. 3. M J. Claverie and A.P. Dupas, Preliminary Evaluation of Ground and Space Solar Electricity Market in 2025, IAF preprint No. 78-187. 4. M.J. Claverie and A.P. Dupas, Forecast of World Electricity Demand to 2025, Impact 29, No. 4, 1979.
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