experiment to prove the Powersat technology and feasibility. Of the options considered, we see the use of Ariane 4/ASAP as the best option. The cost of this option, the autonomous nature of the mission, the possible timescales and the experience of using ASAP in Europe are all in favour of this option. We are concerned over the emphasis on the use of a tether system. We do not believe that the need for an attitude control and propulsion system will be eliminated. Also, the use of a tether will conflict with one of the primary objectives, that of showing that a target can be acquired with sensors and/or the power beam itself. If a tether is used, the system should at least be independent in two dimensions, allowing effective demonstration of target acquisition. Any initial study of the details of a Powersat demonstrator mission should start with the baseline of autonomous spacecraft. Only if the study shows this option as too complex, and too costly, should the tether option be resorted to as a backup. Powers of at least 100W, and preferably higher, should be transmitted. A battery should be used, charged by solar arrays, and fired for a short period at infrequent intervals, as allowed by the charging. Transmission distances of at least a kilometre should be used, and preferably further. Experiments should be repeated over different separation distances to evaluate the accuracy of acquisition, to assess the limits of the equipment as designed, and to investigate how the transmission varies with distance. We would emphasise that the temptation to add subsystems and experiments not central to the demonstrator purpose should be strongly resisted. Small, low cost missions choose simple objectives and do not attempt to complicated matters.
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