I. INTRODUCTION The requirements for energy in the U.S. and the world will continue to increase to support a growing population and to improve the quality of life for that population. Projections indicate the U.S. requirements will grow by a factor of 2 to 3 between now and the year 2000. The manner in which we will meet this requirement is not clear. Oil and gas are expected to be depleted within decades. Fuel for the present class of nuclear reactor systems will also be depleted in the same time frame. The breeder reactor system, when successfully developed, will greatly extend the natural fuel resource but presents continuing safety and environmental concerns, not the least of which is the disposal of nuclear waste as it accumulates from large-scale nuclear energy production. Fusion reactor systems also have potential, but these require significant scientific advances. Coal resources appear sufficient for several hundreds of years. The environmental concerns associated with mining coal, and the subsequent problems or costs in reducing air pollution to an acceptable level during its use, are well known. The logistics of a greatly expanded coal industry is also a significant although not unsolvable consideration. In view of the problems or concerns related to obtaining the required energy from oil, gas, nuclear, and coal sources, the Nation is actively pursuing alternate sources of energy for the future. Solar energy is an obvious candidate for consideration. Solar energy is inexhaustible and clean, and the increasing costs of other sources will make solar energy more attractive in the future. The use of solar energy collected on the Earth has several basic limitations, however, which will tend to inhibit its widespread use. At any given location on the Earth, a solar collector will be limited by such factors as the day-night cycle, cloud cover, and atmospheric attenuation. The day-night cycle, particularly, requires the use of expensive storage capacity or limits the solar application by requiring additional power sources. A concept has been presented ("Power from the Sun: Its Future," Dr. Peter E. Glaser, Amer. Assn. Advan. Sci., Vol. 162, Nov. 22, 1968, pp. 857-861) that is intended to alleviate limitations associated with the collection of solar energy on Earth. This concept involves placing large solar power satellites in geosynchronous orbit and beaming microwave energy down to collection stations on the Earth. Some of the advantages of this concept are that the satellite is in near-continuous sunlight that is not attenuated by the atmosphere, no electrical storage facilities are required, the land use requirement is reduced by a factor of 5 to 10, and the ground power output can be located near the user rather than in desert-type regions.
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