Powersat-type systems could even prove mandatory on low Earth orbits, when the space-faring nations deploy a diverse and cost-effective in-orbit infrastructure. Already in the medium-term future, the development of the International Space Station (Freedom) or the proposed European Manned Space Infrastructure (EMSI) could provide a niche market opportunity for a simple Powersat system. The studies performed for EDF (Powersat study, May 1989) and for ESA (Powersat, an Approach with Commercial Prospects, December 1990) demonstrated that the technologies needed, and in particular those required for energy transmission, were either already available (microwave transmission) or considered possible in the foreseeable future with sufficient efficiency (transmission by laser) and that, generally speaking, the concept was sufficiently attractive to justify the adoption of a dedicated Research and Development programme. One interesting aspect of this prospect is that the intermediate steps to validate the Powersat concept are to a large extent common with those necessary to validate the major sub-systems of a SPS. The possibility of transmitting electrical power at a distance efficiently and safety by microwave or laser beams is naturally the first point to demonstrate by experimentation in both cases. The various engineering problems regarding platform orbit-keeping, energy generation and storage, heat dissipation, station keeping etc. are also the same. However, there are differences: a) The first if that in the case of Powersat, there is no transfer of energy beams through the atmosphere,
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