in such a system would be relatively modest by business standards. The physical system is firmly based upon well developed technology at 2.45 GHz. Because of this, studies have shown that the first low power transmitter should be well under $100000000 [22]. Such a transmitter would provide 16000 kilowatts of rectified DC power to a 200 metre diameter industrial park, with an efficiency of greater than 20% from 60 ~ Earth power to satellite DC power. Average power to one satellite with one Earth transmitter is 240 kilowatts, and 3400 kilowatts with all 14 ground-based transmitters. An All-electronic LEO to GEO Transportation System It is well known that a much better transportation system from LEO to GEO than now exists with conventional chemical rocket propulsion will be necessary to develop space beyond LEO and to make large-scale projects such as the SPS feasible. This is true even if a substantial portion of the material needed for SPS construction comes from the moon. Electric propulsion with its much higher specific impulse could solve the LEO to GEO transportation problem if there were a suitable source of low mass electric power for the electric thrusters. Fortunately, there is. The thin-film format for the rectenna developed by NASA can produce almost any needed amount of power at a mass penalty of only one kilogram for each kilowatt of DC power output. Further, the rectenna sections can be interconnected to make the power available at the high voltage required by such high specific impulse thrusters as the ion thruster and can eliminate much of the current power conditioning with other sources. An all electronic propulsion system that combines the rectenna and microwave beam source with the thruster has been under study for some time, [23]. It has gradually matured to the point where projections of its performance and cost can be
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