<h2>AAS 99-145</h2>
<h2>Determining Precise Orbits for Topex-Poseidon Within One Day of Real Time: Results and Implications                                              </h2>
<h4>B. Haines, S. Lichten, M. Lough, R. Muellerschoen, Y. Vigue-Rodi                                                                                                                    </h4>
Jet Propulsion laboratory                                                                                                                                                 
<h2> Abstract </h2>
We describe recent advances in near real-time orbit determination for the Topex/Poseidon (T/P) altimeter mission. New results suggest that GPS-based orbits computed within one day of recording the last element of tracking data have radial accuracies better than 3 cm in a root-mean-square (RMS) sense. These orbits are used by a variety of specialized users in the oceanographic community in order to support climate forecasting and real-time monitoring of the global ocean. We also discuss prospects for achieving 1-2 cm radial (RMS) accuracies for the Jason-1 (Topex/Poseidon Follow-On) mission, scheduled for launch in 2000. Jason-1 will carry a 16-channel TurboRogue space receiver (TRSR) with advanced codeless GPS tracking technology. The mission will feature a prominent operational component, and the rapid availability of highly accurate orbits will be central to its success.