structure across which is a diaphragm containing the rectenna micro-strips needed to rectify the microwave power (see PART II). Potentially, the rectenna could be attached to the same electrical and mechanical interfaces that otherwise would be used if a second pair of solar array wings were added. This arrangement ensures that the power provided by the Powersat is effectively “transparent,” in the sense that Freedom’s power bus would not know whether the power was coming from the arrays or from the Powersat. This option is dubbed the Microwave Solution because using microwaves are considered the only practical solution for a co-orbiting Powersat at an altitude of 400 km. The principal reason is that microwave systems offer far higher overall efficiencies than possible with lasers. Typically, a global efficiency as measured by the output from the rectenna could be as high as 25- 35%. meaning the size of the solar array on the Powersat must be about 3-4 times the size of an array on the station generating the same power. Although this is a significant increase in area, it is small by contrast to that needed for a laser Powersat where global efficiencies are measured in the “few” percent region. For example, at a relatively optimistic global efficiency of 5%, this would mean the solar array would need to be 20 times larger than for an equivalent integral station array, and 5-7 times larger than for the microwave solution. Such a large surface area would obviously present a very high drag. Other problems are associated with the technology availability of a high- powered laser system, and converting the high-density laser energy into electrical power. Advantages and Disadvantages of the Microwave Solution Quantifying the benefits to Freedom of a Powersat is, of course, difficult to do with any accurate precision given all the operational and technological unknowns. However, the advantages to a space station the size of Freedom are primarily associated with the reduction in the amount of
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