<h2>AAS 95-370</h2><h2>Dynamic Orbit Determination for the EOS Laser Altimeter Satellite (EOS ALT/GLAS) using GPS Measurements</h2><h4>H. J. Rim and B. E. Schutz, Center for Space Research, The University of Texas,  Austin, TX</h4><h2> Abstract </h2>A complete simulation study has been undertaken to assess the EOS ALT/GLAS (GLAS) orbit accuracy based on the fully dynamic GPS tracking technique.  To accomplish the GLAS objectives, the radial component of the orbit must be known with an accuracy of better than 5 cm and the horizontal component to better than 20 cm.  It has been shown that the major source of orbit error at the GLAS altitude (700 km) is the mismodeling of geopotential perturbation.  Even the latest gravity models predict more than 20 cm radial orbit error for the GLAS inclination.  Since the dynamic orbit determination technique has an advantage of tuning gravity field at the GLAS inclination, this investigation places an emphasis on the gravity tuning using GPS measurements.<br><br>