quickly and decisively into space,” provide a new perspective for consideration of the energy-front-space option. The Space Station program does not have a single focus, such as “landing a man on the Moon,” but constitutes a buildup of a broad range of capabilities that represent a stepping stone toward expanded space activities for developing and exploiting the extraterrestrial energy and materials resources of the solar system (2). Space activities are already providing an impetus for many nations to adopt long-range plans that will benefit from economic payoffs from the commercialization of space. Commercial activities in space represent diverse markets where international competitors will be motivated by economic, technical and political considerations. This implies a growing industrial infrastructure to support an increasing variety of commercial and scientific endeavors, relying on routine and affordable access to space. Based upon the premise that the space industrial infrastructure will continue to expand, the development of power supply capabilities for use in space and eventually for use on Earth is receiving consideration ... for example, the development of the power supply for the space station. During the 1970s, alternative directions for developing renewable energy sources in space, based on the SPS concept, were explored by NASA and the U.S. Department of Energy. The objective of the SPS Concept Development and Evaluation program (3) was to develop an initial understanding of the technical feasibility, economic practicality and societal and environmental acceptability of the SPS concept. Both the Office of Technology Assessment (OTA) (4) and the National Research Council of the National Academy of Sciences (NAS) (5) examined the results of this program. The NAS report stated this: The areas relevant to SPS technologies may be investigated in pursuit of goals of other programs. Research should be vigorously conducted and the results evaluated for the implications on the SPS concept. There are uncertainties concerning the availability of large-scale sources of energy of electricity beyond the early part of the next century. The use of coal is of course technically feasible and may set the standard for economic competition, but concerns about carbon dioxide emissions and other environmental effects could constrain coal development. The nuclear breeder reactor is also technically feasible, but it faces problems of political acceptability because of concerns about reactor safety, waste management and the potential for proliferation of nuclear weapons. Even though advances have been made in terrestrial photovoltaic cells, the technology must show further progress in large-scale electrical storage capacity if it is to substitute appreciably for baseload power. Fusion has potential to be of substantial benefit as a long-term source, but has yet to be shown to be technologically feasible. The major criticism of the SPS in the NAS report revolved around the use of single-crystal silicon solar cells for the SPS reference system (6). This system was presented by NASA as a tool for inquiry, rather than as the design for an SPS that would actually be constructed, and was based on extensions of known 1970s technologies. In addition to the Space Station program, a major stimulus to the advancement of space technologies is the strategic defense initiative (SDI). The space technologies that are expected to be developed in support of SDI include space transportation, beamed energy, power generation and automation. Historically, technologies developed for military purposes had an important influence on civilian technology
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