perturbed by the space plasma environment in low Earth orbit. This is not considered a trivial problem and mandates a space experiment with reasonable power densities. It is important to remember that the first microwave-based Powersat must operate in low Earth orbit for the space station power supply. For lasers, space plasma interactions are not a concern and, therefore, the initial demonstrator would not need to generate high power densities. However, as lasers can only be used from high Earth orbit where aerodynamic drag on the large solar arrays is minimal, the key technology to be proven in an initial demonstrator is the ability to track a moving target a significant distance away. As these requirements almost precisely match those of the SILEX intrasatellite communications systems, it was decided that a there would be little advantage in performing an equivalent ASAP laser experiment For this reason, only a microwave ASAP reference concept is proposed here. Laser technology is a long way behind microwave technology in terms of its applicability to operational systems. Therefore, the emphasis of the laser Astro-SPAS advanced demonstrator should be to develop technologies critical to an operational laser system. Specifically, such technologies include a high power, high-efficiency and light-weight, laser system (e.g. solar pumped), thermal management techniques for this laser, a very high precision pointing system (<0.1 arcsecond), and the technologies for reconverting the laser energy efficiently into electrical power. This issue of global system efficiency is probably the most urgent, and improvements by at least an order of magnitude are considered mandatory for laser systems to be competitive with microwave approaches. Should a reasonable technical solution be found for the laser Astro-SPAS advanced demonstrator, its inherent characteristics would enable space-to- ground SPS-type power transmission experiments. The synergism between a laser Powersat and SPS is very strong and using a laser is considered one of the
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