Figure 10.1.1 Arecibo Observatory, Puerto Rico [Ostro, 89] The first of these makes use of the fact that Arecibo has two different modes in which it can move its antenna. One of these is a finely controlled motion used for tracking planets and other celestial bodies; the other is a slew mode used for rapid, but less controlled adjustments to pointing. By transmitting while in the slew mode, it was thought that it might be possible to track the satellite as it went overhead. Unfortunately, the slew rate is not very fast: it can move at 24°/min in the azimuthal direction but only 1.85°/min across the zenith. This is not fast enough to track a satellite in a low orbit, though it might be used for one at 5,000 km altitude or greater. Another possibility suggested by Brian Tillotson is to set up a dual mirror system underneath the transmitting antenna. By sliding the second mirror along in a preset direction it might be possible to shift the effective pointing angle rapidly and track a satellite's orbit. It must be emphasized here that both of the above ideas are very rough; it could be that neither of them is feasible, or that some other method could be used to allow Arecibo to track more quickly, or that it can't be done at all. In the latter, not unlikely case, one immediately thinks of the large military phased array radar systems which have been used over the last decade to track ballistic missiles for an early warning system. Though not as large as the Arecibo facilities, these radar systems have excellent tracking capabilities and can operate (perhaps only in pulsed mode) at high power levels. Examples of this kind of military radar include the Alaskan PAVE-PAWS, the Thule system in Greenland, the installation at Kwajelein in the Pacific, and new NATO radar systems in Portugal, Italy, and Greece. Corresponding Russian radar systems exist, though the most promising candidate seems to have been destroyed as part of a US-FSU arms reduction pact just a few months ago. Unfortunately much of the information necessary to evaluate these systems is still classified, so it is hard to judge their suitability for this particular activity. One major advantage of using such a system for this sort of experiment is political in nature. The public relations potential of using a military facility to conduct experiments aimed at providing clean, safe future power sources for the developed and developing countries would be immense. Leaders around the world are looking for ways to turn their military investments to peaceful uses, in effect turning swords into plowshares. The military would likely be enthusiastic about such an idea as well, if only as a way of justifying the maintenance of their own facilities. Finally, the people of many Western countries who have long been looking for some sort of peace dividend from the end of the Cold War would probably embrace the project as well. Any positive publicity associated with the demonstration would improve the overall image of space solar power, and that is certainly worth pursuing.
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