<h2>AAS  96-183</h2><h2>ORBIT ESTIMATION RESULTS FOR TOPEX/POSEIDON BASED ON GPS TRACKING DATA</h2><h4>E. R. Swift, M. J. Merrigan, and M. W. Gouldman, Naval Surface Warfare Center</h4><h2> Abstract </h2>The Naval Surface Warfare Center, Dahlgren Division, developed and maintains the OMNIS orbit computation system that the Defense Mapping Agency uses to generate its precise Global Positioning System (GPS) orbit and clock estimates.  This system has been recently upgraded to process GPS satellite-to-satellite tracking pseudorange and carrier phase data collected onboard a host vehicle for estimating precise host vehicle orbits.  A brief overview of the capabilities of this software system will be given in the first part of the paper.  The second part of the paper will summarize the results of applying these capabilities to a TOPEX/POSEIDON data set.<br><br>