<h2>AAS 95-411</h2><h2>Semi-Autonomous Spacecraft On-Board Ephemeris Propagation</h2><h4>A. H. Salama and J.  Kangas, Jet Propulsion Laboratory, Pasadena, CA</h4><h2> Abstract </h2>Autonomous navigation can be accomplished by automating and migrating orbit determination, trajectory propagation and maneuver design to the spacecraft.  This paper is concerned only with semi-autonomous on-board trajectory propagation.

Two strategies are presented.  One implements a semi-analytic method and rectifies, when needed, a simple on-board (on-line) ephemeris.  The method is called rectification in which only several parameters are uplinked to the spacecraft infrequently.  The other strategy applies the lessons learned from TOPEX/POSEIDON ephemeris representation to build a data compression device for a wide range of orbits.  A trade-off study is conducted to relate accuracy requirements with semi-major axis and eccentricity to minimize frequency of uplinking.<br><br>