The vulnerability of the rectenna to overt military action, terrorist attack or sabotage is not greatly different from that of other large utilities. Rectenna operation, however, is not dependent on a critical fuel supply line such as coal or oil, which can be rather easily interdicted,2 rendering the rectenna to that extent less vulnerable than other large power plants. Concealment, hardening, protective sheltering and other measures can provide limited protection. The rectenna will be part of an interconnected utility grid, so that the loss of any one station (or satellite) is not necessarily critical. The large size and inherent redundancy of the satellite would also protect it from all but the most unlikely meteor showers or individual hits.3 More significant factors in earth orbit are heat transfer, vacuum, particulate and ultraviolet radiation and interactions with the plasma. Assessment of these environmental effects is hampered by lack of experience with large spacecraft but is proceeding at a theoretical level. 1.3 Is there a way that rivals, unauthorized personnel, etc., can gain control of the SPS? A fully operational SPS for the United States might consist of 60 satellites, a like number of rectennas, a transportation complex and a highly redundant command and communications subsystem. There is no credible way that this system could be commandeered short of war. The power beam from an individual satellite to its designated rectenna is enabled and controlled by a pilot beam. The pilot beam (which may be redundant for purposes of reliability) provides the information to the satellite to focus the power beam and to keep it precisely pointed at the rectenna. If for any reason the transmitting antenna is pointed away from the rectenna, the power beam defocuses and becomes indistinguishable from the background noise. The pilot beam is coded to operate only with its designated satellite and to preclude its duplication from an unauthorized source. "Key Crude Oil and Product Pipelines Are Vulnerable to Disruption", EMD-79-63, U.S. General Accounting Office, August 27, 1979. 3Space and Planetary Environment Criteria Guidelines for Use in Space Vehicle Development, 1977 Revision, NASA Technical Memorandum 78119, November 1977. ^SPS Reference System Report, DOE/ER-0023, October 1978, pp. A42-A44.
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