All of these numbers would seem to make Arecibo an ideal facility for the type of demonstration envisioned except for the problem with tracking. Figure 2 shows the tracking rate necessary for satellites at various orbital heights. For a satellite moving at about 8 km/sec in a 1000 km orbit, tracking on the order of 0.5°/sec is necessary. Tracking at this rate is not within Arecibo’s nominal capabilities, but it is conceivable that some creative modifications could give the facility a limited tracking capability. One possibility for this sort of modification 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 slew mode, 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. Even in those situations, however, it is unclear whether the control level in slew mode would be good enough to keep a satellite within the transmission beam spot. Still, it does seem possible that the slew systems could be modified to give better performance in specific situations. For the remainder of this paper, design trade-offs will focus around the use of Arecibo as the primary transmission source. This does not mean, however, that the military systems described above will have no role. For the best of these systems the average power received by the satellite would be on the order of 1% of that received
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