<h2>AAS 95-366</h2><h2>An Analysis of the TOPEX/Poseidon Operational Orbit:  Observed Variations and Why</h2><h4>R. B. Frauenholz,  R. S. Bhat and B. E. Shapiro, Jet Propulsion Laboratory, Pasadena, CA, R. K. Leavitt, Sterling Software, Inc., Pasadena, CA</h4><h2> Abstract </h2>Following launch on 10 August 1992, TOPEX/Poseidon began and continues a very
successful global study of the earth's ocean circulation using a combination of
dual-frequency radar altimetry and precision orbit determination. A joint
mission of NASA and the French Space Agency CNES (Centre National d'Etudes
Spatiales), TOPEX/Poseidon has completed its three-year primary mission and has
begun a three-year extended mission phase.

Precision orbit determination (POD) performed by the Goddard Space Flight Center
(GSFC) using laser ranging and DORIS tracking data (CNES) defines radial
position relative to the geocenter to an unprecedented accuracy of ~5 cm RMS.1
The POD results are utilized to accurately reconstruct the operational orbit
history in terms of precise classical mean elements.  This paper explains
observed variations in the mean orbital elements and their effect on the
satellite's 10-day repeat ground track, which has been successfully maintained
within the stringent #1-km control limits in equatorial crossings.
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