- In the Laser Solution, three operational Powersats would be located in a higher orbit (7,500 km) and provide power to Freedom during eclipse passages. (Figure 3) As a result, both station-keeping propellant and battery mass savings would be realisable. Battery savings result because they would not be cycled as frequently, thereby lengthening their lifetime. • Based on existing technology, it appears that only a microwave design can be used for a low-Earth orbit Powersat because its drag coefficient would be much less than an equivalent laser-based design. (This assumes power is generated with photovoltaic cells.) Typically, the global efficiency of microwave-based designs is on the order of 25%, whereas for laser-based designs it is about 1-3%. Likewise, it appears that only lasers can be used from high-Earth orbits because their very tight beams allow the power reconversion equipment on the station to be kept relatively small. This situation would change with the anticipated improvements in laser efficiency. • These two solutions have inherent advantages and disadvantages. - The Microwave Solution appears technically feasible with existing technology. However, as the single Powersat would need to fly in close formation with the space station - decaying and re-boosting at the same time and rate - it could probably only serve one user at a time. - The Laser Solution, by contrast, has greater potential because it could service several users simultaneously. However, this potential is tempered by the fact that such Powersats would require a significant investment in laser systems and reconversion technology. • The Powersats in both these solutions would be launched as fully integrated spacecraft - analogous to large communications satellites. Ariane 5, for
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