perspective of technology, therefore, it is considered that low power laser beam passage through space can be adequately proven in ground demonstrations. Similar arguments can be made for the reception of laser power and reconverting it into electricity. Microwave Discussion Technology availability is not a severe problem for a microwave demonstrator, or perhaps even the full-scale operational Powersat, as discussed in PART I. However, there is one important technical issue for which ground-based experiments are inadequate and that necessitates a spaceflight. This is in the area of non-linear space plasma interactions. A good explanation of the problem is described in an ISAS report on their proposed Microwave Energy Transmission in Space (METS) experiment. [25] Since the space environment is not a simple vacuum but is filled with plasmas, the propagation characteristics of the microwave energy beam is not so simple as in the vacuum. The high intensity electric field of the microwave beam causes the modification of the medium in such a way that the beam itself suffers a filamentation of the beam. This will be a serious problem for long-distance energy transmission as the nonlinear plasma nature will modify the propagation path and thus give rise to a mis-transmission to a wrong target other than the receiving site. Such filamentation instabilities have not been studied in detail at all and no quantitative prediction is available. Much experimental as well as theoretical works are necessary. Communications satellites routinely beam power on the order of a few hundred Watts to Earth. However, non-linear plasma interactions are small and unnoticed because the beam covers wide areas on the order of “tens" of kilometres for spot beams to “thousands” of kilometres for global beams. As a result, slow changes in the beam direction go unnoticed. Further, the power density is relatively low. For Powersats, non-linear effects could be severe because the power
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