The ATS 6 satellite, during an orbital maneuver in September 1976, passed within a few hundred kilometers of the geosynchronous satellite 1976-059A. Analysis of the 30- to 80-keV electron data from the University of California at San Diego (UCSD) electrostatic analyzers on ATS 6 and the 30- to 300-keV electron data from the Los Alamos Scientific Laboratory instrument on 1976-059A during this period reveals good agreement between the two instruments even when the separation is ¿7¿. The low-energy UCSD ion data from ATS 6 allow a simultaneous determination of the potential difference between ATS 6 and th ambient medium. Use of the 1976-059A electron data to approximate the ambient plasma electron density and temperature during these charging periods indicates sufficient information exists in order to estimate the maximum potentials to which ATS 6 charges in sunlight an eclipse. As data from 1976-059A and similar satellites are potentially available in real time, the information therefore exists to create a satellite charging index for the geosynchronous regime that would be valid within at least ¿7¿ longitude of the position of each measurement.