over 30 kW across one mile with an overall efficiency of 84%. This proved that large-scale power beaming could be a reality. In a $20 M study NASA and the US Department of Energy (DOE) examined the problem and proposed a point design for a system of 10 km by 5 km platforms of silicon photovoltaic cells in geostationary orbit beaming to 5 km square rectennas on Earth, the same principles that Glaser had used. Although the study results were positive a National Academy of Sciences overview of the study recommended further study rather than deployment, principally due to unacceptably high launch costs. Figure 1.2 The NASA/DOE Reference SPS In 1985 a proposal was made by David Criswell and Bob Waldron to cover large sections of the moon with solar cells and beam the power from there to Earth. The potential for utilisation of non-terrestrial materials in satellite manufacture was first observed by Gerard O'Neill in the mid nineteen seventies. The first activity in this area had been two studies examining their utilisation in the reference concept from the NASA/DOE study. General Dynamics and MIT concluded respectively that 90% and 94% lunar material use was possible in solar power satellite construction. A different approach was used in a study commissioned from Space Research Associates (SRA) by the Space Studies Institute (SSI) in 1985. This study was not limited, as the others had been, to direct substitution of non-terrestrial materials into the NASA reference design concept and considered solar power satellite designs optimised for non terrestrial material use. SRA concluded that solar power satellites could consist of over 99% lunar material, with a significant cost advantage. In a follow-up study in 1989, SRA considered more constrained models for the availability of non-terrestrial materials, with only materials obtained using simple processing techniques available, such as glass and iron. Since that time there has been renewed interest in space power. In 1987 the Canadian Stationary High Altitude Relay Platform (SHARP) program demonstrated power beaming to an airplane, with the aim of providing a high-altitude communications platform for Canada. Figure 1.3 shows a picture of the test airplane is shown. This program is ongoing, with a larger demonstration in preparation.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==