A more subtle possibility is to spoof the telemetry, tracking, and control (TT&C) signals from a ground station. These signals tell satellites when to turn on and off, when to conduct maintenance routines, and how to position themselves. A commercial satellite system could be rendered inoperative by simply manipulating the TT&C signal so as to instruct all satellites in a system to disable themselves. Spoofing a satellite signal, however, can also be a low-payoff proposition, as shown once again by GPS, which is a special case in this respect. Commercial GPS is already, in effect, spoofed -- that is, by Selective Availability, which deliberately produces a less accurate signal -- but countermeasures are already available. A commercial system known as Differential GPS determines the induced error by reference to a known position on the Earth and transmits a correction to subscribers. It is not likely that even a technologically unsophisticated adversary, already dependent on satellite positioning, would long be susceptible to the spoofing of a GPS signal.

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Black, J. Todd. "Commercial Satellites: Future Threats or Allies?." Naval War College Review. (Winter 1999). [ 2 quotes ]