b) The second is that the economy of Powersat systems makes them economically profitable on a much smaller scale than the SPS. Because of a) it is possible to postpone the full study of the interaction effects of powerful beams with the Earth’s environment until after the energy transmission technology has been fully proved in space. Because of b) it is possible to engage in operations without having to collect the enormous financial means needed for the development of even a SPS of modest proportions. This situation makes it attractive to use Powersat development as an intermediate step towards the development of a full SPS programme. The latest EUROSPACE study Powersat - a Pragmatic Economic Assessment of Future Powersat Operational Concepts and Prospects for an Inexpensive/Near Term Powersat Demonstration Programme - ESA contract N° 9390/91/F Final Report, March 1992) not only confirmed the results of the previous studies, but made it feasible to identify the possibility of engaging in a relatively inexpensive demonstration programme. At the present moment, several experiments involving energy transmission in space have been proposed by various organisations for International Space Year. The following are, for example, mentioned in a paper prepared in the spring of 1992 by the IAF Power Committee: • A three-phase experiment, proposed by the U.S. Center for Space Power (Texas, U.S.A.), to use the space shuttle for transmission by microwave beams at frequencies ranging from 2.45 to 35 GHz at a power level of some 250 W (RF) and distances on the order of 20 m. • A microwave energy transmission in space (METS) proposed by the SPS working group of ISAS, using a sounding rocket and a subsatellite to transmit some 1000 Watts at frequencies on the order of 2.45 GHz. • A laser transmission experiment proposed by EUROSPACE between the space shuttle and an Astrospas platform (developed by MBB/ERNO). At the time when this proposal was put forward, EUROSPACE had not thought it useful to propose a microwave experiment, but decided to focus on laser transmission. This position was due to the feeling that the maturity of microwave transmission was such that it was not justifiable to embark on a costly programme of space demonstration to prove them. The concentration was therefore on the less mature technology of laser transmission.
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