Interferometric tracking for close geosynchronous satellites

An experimental approach to the monitoring of the relative orbital motions of closely operating geosynchronous satellites is presented. A radio-interferometer tracks two satellites so as to measure the differential pointing angles of the satellites, and this allows the relative motions of the satellites to be estimated on a real-time basis. Interferometer hardware and its common-error cancellation performance are described, and the real-time filtering of relative motions is discussed. Filtering results indicate that this approach can potentially monitor relative positions to a few hundred meters.