An Analysis Of The Topex/Poseidon Operational Orbit: Observed Variations And Why

Following launch on Aug. 10, 1992, TOPEX/Poseidon began a very successful global study of the Earth's ocean circulation using a combination of dual-frequency radar altimetry and precision orbit determination. The 1336-km nearly circular frozen orbit and 10-day repeat ground track have been closely monitored and accurately controlled using precise mean orbital elements. A new osculating-to-mean conversion technique designed specifically to meet the stringent TOPEX/Poseidon orbit control requirements removes all short and long-periodic geopotential and third-body gravity perturbations acting over 10 days. The most important orbital parameter, mean semimajor axis, demonstrates stability and consistency to 13 cm rms using a 20 x 20 geopotential field. The mean semimajor axis exhibits unique behavior with intervals of either orbital boost or deboost induced by along-track forces of body-fixed origin that change magnitude and direction depending on the satellite yaw-control mode and solar array articulation strategy. Nine orbit maintenance maneuvers, recently augmented by selective use of solar array articulation, have maintained the semimajor axis within +/-5 m of the reference value, thereby keeping the ground track within the +/-1-km equatorial longitude control band. Other orbital parameters remain within required limits without dedicated maneuvers.