The reference SPS design was developed using separate “rigid” photovoltaic arrays and microwave transmitting antenna. Significant problems encountered were the mass of the satellite, and associated transportation costs, and the need for high power levels, and thus high capital costs, to amortize the large antenna/rectenna required for efficient power transmission. In this paper we discuss a possible way to reduce these problems by integrating the solar cells and microwave transmitter/ antenna into monolithic building block units. These units may then be replicated as desired to create a structure whose light collection area is also used as the transmitting aperture. The total satellite mass could thus be reduced by eliminating antenna structural elements and a majority of the power conditioning and distribution wiring. Further, because of the larger aperture, this integration could yield a narrower microwave beam at the receiver(s) at much lower power levels, allowing smaller unit size power satellites. In many ways this is similar to an earlier solid-state SPS design [5], which addresses several of the issues such as heat-rejection not discussed here, and incorporates a turning mirror to direct sunlight to an Earth-facing solar/microwave array. By using thin-film technology, the current conceptual design should be somewhat lighter. Micro-phased Array Distributed SPS In the highly-integrated SPS design proposed [8], microwave oscillators and dipole antennas are integrated directly with the solar cells, using phased-array techniques to steer the beam to the receiving antenna(s). Rather than a smaller number of high-power (kw’s) microwave tubes, the integrated SPS will have hundreds of thousands to billions of self powered integrated transmitters, each operating at low power. This integration would eliminate the power conditioning elements and the wiring used for power distribution, reduce the waste thermal management subsystem to small self contained radiating surfaces, and eliminate a separate discrete antenna. The state of technology development in solid state electronics and solar cells indicate that such an integration could be performed. It may even be possible to design a solar power satellite to be constructed entirely by thin-film technology, consisting of thin (one to two micron) active components on a plastic substrate. The potential thus exists for technologies currently under development, thin-film photovoltaics and solid state microwave and computational electronics, to considerably reduce the mass-to-orbit required for such a satellite power system. The proposal consists of the following elements: —Total integration. Microwave transmitters are integrated directly at the solar cell level. No wires or power management/distribution system is required. —Thin-film construction. Lightweight photovoltaic films, and possibly thin
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