microwave power transmission could be fifty to seventy percent efficient, had been published in the literature (2). Building large space structures measured in kilometers seemed unthinkable in the early 1970s, and still does to some skeptics. But all of the studies of this problem have readily developed plausible concepts for doing so. These concepts are undoubtedly naive as almost all early engineering concepts are, but history shows that early naivety usually errs in overestimating the difficulty of the problem. The literature abounds with statements to the effect that the state of the art of control systems falls far short of the requirements, but the quantitative studies and simulations that were carried out during the SPS studies indicated that relatively simple control schemes would work. Because the launch of a large rocket is a spectacular display of energy consumption, it is natural to surmise that launching SPSs would consume more energy than they could ever produce. The very simple calculations that demonstrate the opposite were apparently never carried out by the early critics of SPS. This reminds us of the critics of Prof. Robert Goddard circa 1925, who argued that it was “physically impossible” for a rocket to reach the Moon. The calculations that prove otherwise are equally simple. The world of space transportation circa 1970 was dominated by the Saturn V. In 1969, Saturn V accomplished the astonishing feat of sending men to the Moon. One can multiply Saturn V’s space transport cost per unit mass by the estimated mass of an SPS, arriving at a figure like the GNP of a large industrial nation. Such calculations were, in fact, made, with the inevitable dismissal of SPSs as uneconomic pie in the sky. NASA studies as early as the mid 1960s, however, had forecast eventual space launch costs two to three orders of magnitude less than those of the Saturns. In 1973, the first OPEC oil embargo alarmed the world about the “energy crisis” foreseen for many years by knowledgeable investigators such as Hubbert. Of course, many viewed the whole affair as either a nefarious plot by the oil companies or the result of bureaucratic meddling with the economy. Waiting in line for gasoline made every American acutely aware of the problem. The 1973 crisis catapulted solar energy from the realm of eccentric scientists into one of serious alternative energy technologies. Although most of the enthusiasm was for terrestrial solar, the SPS concept was dragged forward on the coattails of this movement. By this time, NASA had funded an initial study of SPS (3). The study concluded that the idea was technically feasible and could deliver net energy. By 1975, technical papers on SPS had become an appreciable, though small, element of energy technology literature. A general attitude of technical incredulity still existed, and SPS was subjected to several technical audits by NASA, DOE, and industry. None concluded that SPS was technically unworkable. All saw it as a towering engineering challenge with exceedingly uncertain economics. A beneficial outcome was viewed as at least possible. At the end of 1976, NASA initiated SPS system definition studies with industry. These were funded much more generously than earlier work, and began to develop details of SPS concepts. The growing SPS technical community began to sense an air of reality in the idea, whereas earlier studies had been motivated mainly by academic curiosity. Some of the papers published in 1977 and 1978 were outright advocacy pieces, with a distinct flavor of SPS being the next great Apollo project. This attitude was not welcomed by the Carter administration, which viewed conservation and coal as the solution to the energy crisis. Carter was so opposed to an Apollo-like program that an express
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