Figure 1.3 The 1987 SHARP test airplane. In Japan there has been particular interest in space power. The Japanese MINIX sounding rocket experiment demonstrated small-scale beaming over short distances in space in 1983. A more complicated version of MINIX, the Microwave Electric Transmission from Space (METS) involves an experiment to be launched in 1993, to examine power beaming and related areas in plasma physics. The first flight of MILAX, a microwave powered aircraft using a FET phased array transmitter steered with a pilot beam, is imminent. The ISAS Solar Power Satellite Working Group is using the results of all these studies as a basis for larger scale work. The group has designed SPS2000 as a strawman model for future work. The current design is intended to beam megawatt-level power from an equitorial orbiting satellite to simple rectennas on Earth. A schematic for SPS2000 is shown in Figure 1.4. Other realistic schemes for testing power beaming on smaller scales have been proposed, notably at SPS ‘91, a conference in France at which almost 100 papers were presented to an audience of interested scientists and engineers. It now appears certain that there exist markets for which power beaming could be economical, even in the medium term. While many people have proposed individual designs for hardware, there has yet to be a study outlining a possible evolutionary path to large scale solar power transmission for use on Earth or elsewhere. This is important because a system design that involves massive investment and requires answers to many currently unanswered questions has no hope of being built, whereas a single experimental satellite offers no vision. A more gradual evolutionary approach holds much more interest, and that is what is presented in this report.
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