technology does not yet exist to support development of a full-scale Powersat. However, if such a laser proves practical, it holds the promise for transmitting power over great distances which is important for supplying multiple users. Lasers and microwaves both have advantages and drawbacks, as discussed below: Laser Discussion For the initial demonstrator, the issue of technology availability is not severe. Whereas a laser-based operational Powersat would need to supply power on the order of “hundreds” of kWs, the initial demonstrator would be limited to a few “tens” of Watts because of the restrictions of supply power. A variety of lasers exist at these low power levels. However, the few that are qualified for space applications have very low power levels. For example, the diode lasers developed for the SILEX intra-satellite optical communications system have power ratings of only 60 and 500 mW. (See Appendix) For the advanced demonstrator, a laser capable of producing several “hundreds” of Watts would be needed and. therefore, require significant development work. This fits in with the higher cost/longer term characteristics of the future experiment, as will be discussed in Section 5.2. The key technology that an initial laser demonstrator would need to prove is the production of a tight beam that remains locked onto a target situated a great distance away - many tens of kilometres, for example - for an extended period of time. Demonstrating that laser beams can be transmitted and received through space is not so important because non-linear interactions with the space plasma are insignificant. This is because the frequency of laser emissions is some 108-109 times higher than ionospheric and magnetospheric plasmas. From the
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