<h2>AAS  96-142</h2><h2>THE INCLUSION OF THE NAVAL SPACE COMMAND SATELLITE THEORY PPT2 IN THE R&D GTDS ORBIT DETERMINATION SYSTEM</h2><h4>P. J. Cefola and D. J. Fonte, Charles Stark Draper Laboratory</h4><h2> Abstract </h2>Previously, the workstation version of GTDS Orbit Determination Program was modified to include the operational General Perturbation solutions:  SGP, GP4, HANDE, and SALT.  The current work adds the Naval Space Command PPT2 model.  The interface with PPT2 follows the standard GTDS Orbit Generator architecture.  The analytical and software aspects unique to PPT2 are described.  Testing of the GTDS PPT2 capability includes:  (1) comparison with orbit propagation benchmark cases supplied by Naval Space Command, (2) testing of the GTDS PPT2 Differential Correction capability with truth data generated by GTDS, and (3) testing of the DC capability where the truth data are actual orbits generated by a source external to GTDS.  Together with existing numerical and semianalytical options, this gives GTDS a comprehensive set of orbit propagation capabilities.<br><br>