advantage of, the peoples' insistent demand for improvements in living standards could be very difficult to meet. In the SPS concept which has been the basis for most current studies, solar cell arrays would convert solar energy directly into electricity and feed it to microwave generators forming part of a transmitting antenna. The antenna would precisely direct a microwave beam of very low power density to one or more receiving antennas at desired locations on earth. At the receiving antennas the microwave energy would be safely and efficiently converted into electricity and then transmitted to users. An SPS system could consist of many satellites located in geosynchronous orbits about 36,000 km away from the earth's equator so that each satellite would be stationary with respect to any desired longitude. The SPS concept has been given serious consideration in many countries, including Austria, England, France, Germany, Japan, the Soviet Union and the United States, and by United Nations bodies, particularly the Committee on the Peaceful Uses of Outer Space. The most extensive studies have been performed by the U.S. Department of Energy, which has evolved an SPS reference system. The satellite portion of this system would consist of solar cell arrays covering a 5 x 10 km area. A 1 km diameter transmitting antenna would direct the microwave beam to a 10 x 13 km receiving antenna on earth, where 5 million k W could be delivered nearly continuously. INTERNATIONAL IMPLICATIONS OF THE SPS As the benefits of the SPS system will extend beyond national frontiers, the development decision should not be left exclusively to national jurisdictions but be made part of transnational affairs. Developing countries should be given opportunities to participate. The SPS concept should advance the complementary national interests of both developed and developing countries because its benefits are global. In view of the extended time scale for the research to establish the overall feasibility of the SPS concept and for subsequent engineering development and verification phases culminating with a prototype SPS in about 20 years, followed by commercialization, it is unlikely that the impacts of the SPS will be felt by Third World countries for at least the next 40 years. A similar time scale will be required for terrestrial solar energy applications or any other alternative energy source which might have a significant impact on world energy supply. The SPS has the potential of revolutionizing the standard of living in developing countries, not only by directly providing a source of power for cities, transportation systems and industries, but indirectly, by powering chemical synthesis plants providing liquid fuels for dispersed populations. The latter would release billions of tons of dung and firewood for other uses and thus provide major ecological benefits to those parts of the world most severely threatened by increasing fuel shortages. The shift from nonrenewable to renewable fuels in the developed countries would stabilize the prices of nonrenewable fuels, thus making them more available to Third World countries. New policies will be required to guide decisions regarding the future course of SPS development from a global perspective. International agreements will require not only participation by all countries which could benefit from an operational SPS, but, more importantly, an appreciation of the opportunities and challenges which will face the introduction of a global SPS system. Institutions in developing countries, for example in India, have expressed serious interest in the SPS but much more infor-
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