array. However, it is a close analogue to what will be required in the Solar Power Satellite, differing mostly in the format of the conventional magnetron. The existing hardware uses the efficient, low noise, very low cost, and highly available conventional microwave oven magnetron. The space version would use a magnetron specifically designed for space use. The design for such a tube has been worked out in great detail under a DOE/NASA contract [2], and is exhibited and described in Appendix A. [Editor’s. Note: Appendix and a list of references citedfollow this white paper.] The specific experimental work that is recommended is to use two or more ESPAMs to demonstrate electronic steering in a phased array. If the support for such a demonstration is severely limited then the experiment would be configured to use the two slotted waveguide array antennas that now exist, one brass board MDA that exists, and another microwave oven magnetron operated as an oscillator and to which the MDA is slaved. Then a phase shifter between the two to vary the phase difference in the output power from the two antennas would demonstrate beam steering around one axis. If substantially more support were available, then more slotted waveguide arrays should be fabricated and more MDAs produced of a design that would more closely approximate a design for large scale production. Of these two actions, the second is to be desired, for as a result it would then be possible to replicate the ESPAMs in high volume and to build ground based arrays for use in microwave powered high altitude vehicles as described in reference [1] or, as a second phase, to build larger arrays somewhere on the Earth’s equator and so begin the development of sending power into space for industrial parks orbiting in low Earth orbit, or on a larger scale, to beam power to interorbital transfer vehicles which are electric powered to reduce transportation costs in placing Solar Power Satellites into geostationary orbit. The latter application, supported by NASA/LeRC, has been studied in considerable detail in a 160 page report. [3] Viewed in this way, and starting with the simplest of demonstrations and existing technology, we have a format for an electronically steerable array that closely approximates that used in the Solar Power Satellite and that can be used in progressively more mature forms to beam power into space. Eventually it would be used to help place the Solar Power Satellite system into geostationary orbit. Refinement of Technology Again we can be quite specific about technology refinement. As an introduction to this discussion we note that the electronic device that can best meet, now or in the foreseeable future, all of the requirements imposed by the SPS upon a microwave generator in space is the magnetron. These requirements, all of which must be met simultaneously are: 1. Very high efficiency at all power output levels to reduce the amount of heat that must be radiated to space. 2. Operation at high temperature to take advantage of the relationship that the quantity of heat radiated is proportional to the 4th power of the absolute temperature. 3. Symmetrical geometry that permits the efficient attachment of a heat radiator. 4. Function as a high gain amplifier with the phase of the output power always in phase with the input drive. 5. Very low level broadband noise.
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