TOPEX/Poseidon Operational Orbit Determination Results Using Global Positioning SatellitesResults of operational Orbit detemination, Performed as part of the TOPEX/Poseidon (T/P) Global Positionin Satellite (GPS) demonstration experiment, are presented in this paper. Elements of this experiment include the GPS satellite constellation, GPS Demonstration Receiver on-board T/P, six ground GPS receivers, the GPS Data Handling Facility and the GPS Data processing Facility (GDPF).