oceans, in the atmosphere, or in outer space, nor the Strategic Arms Limitation Treaty could have been achieved without the availability of such satellites. The technology developed for these satellites, originally for the goal of national survival, is now being turned to directly peaceful purposes through the development of satellites for the measurement of temperature and wind velocity distributions in the atmosphere, of patterns of land use, of ground water, of forest coverage and vitality, of deforestation, of the salinity of water, of ocean temperatures and wave heights and directions, and of mineral concentrations including petroleum. II. SOME ULTIMATE POSSIBILITIES IN SPACE So far we have mentioned what has already been achieved in space or what will be implemented very soon. Let us turn now to a brief consideration of what space could ultimately mean to all of us. Because space programs in more than a dozen nations around the globe are no longer “news,” further expansions of the potential capabilities of space activities for the improvement of the human condition have not yet been appreciated by most of the Earth's population. Within the past decade, the expansion of scientific knowledge and of the technical capability has reached the point that the nations of Earth can, and should, consider opening resources of energy and materials in space many thousands of times greater than all the resources of the Earth; this can be done within a very short time-scale, as little as one or two decades. The resources in question are energy, now wasted, which streams outward from the Sun endlessly, in the form of intense, unvarying sunlight in space outside the Earth's shadow, and materials, now totally unused, in the form of lunar soils and the asteroids of the solar system. The unlimited energy available in space may be harnessed for use here on Earth in several different ways. Large, very lightweight mirrors in orbit around the Earth could illuminate, on demand, specific areas on Earth on either the daylight or the night sides of the planet. Such orbiting mirror systems could be used for illumination of crops near the freezing point to reduce losses to frost; for illumination of urban areas, reducing or eliminating the need for street lighting systems; for illumination to permit night harvesting or to assist night operations in disaster relief and rescue; to stimulate the growth of crops for biomass energy conversion; or for direct conversion of more intense sunlight (available 24 hours a day in this manner) into electricity by well-known means on the ground. Alternatively, full-time sunlight could be captured in geosynchronous Earth orbit, converted into some acceptable form such as low-density microwaves for transmission to a receiver station on the surface of the Earth, and its conversion on the ground into useful forms to provide a full-time renewable energy source. In highly industrialized regions, such Solar Power Satellites would likely be used to provide electricity. Elsewhere, the energy delivered from space could be used to produce synthetic liquid or gaseous fuels, such as methanol (produced from air and water) or hydrogen (by electrolysis from water), to produce synthetic fertilizers such as ammonia (from air and water), or to desalinize ocean water for human consumption and for agriculture. At the present time, a number of uncertainties concerning the environmental acceptability, economics, and technical practicability of Solar Power Satellites remain to be resolved, but the idea clearly merits serious consideration. An alternative approach to the construction of such Solar Power Satellites has been developed in a series of four conferences, three government-supported techni-
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