Precision orbit determination for TOPEX/POSEIDON

TLDR

The TOPEX/POSEIDON mission requires radial position accuracy better than 13 cm RMS, an order of magnitude below prior altimeter missions. The study established the TOPEX Precision Orbit Determination (POD) Team, a joint effort among NASA Goddard, the University of Texas at Austin, the University of Colorado, and JPL, to meet this objective. The POD team improved, calibrated, and validated precision orbit determination software during prelaunch development and postlaunch verification. Accomplishments included improved gravity and surface force models and better laser ranging and Doppler tracking, leading to radial orbit accuracy of 3–4 cm RMS, which enables unprecedented ocean dynamic topography determination.

Abstract

The TOPEX/POSEIDON mission objective requires that the radial position of the spacecraft be determined with an accuracy better than 13 cm RMS (root mean square). This stringent requirement is an order of magnitude below the accuracy achieved for any altimeter mission prior to the definition of the TOPEX/POSEIDON mission. To satisfy this objective, the TOPEX Precision Orbit Determination (POD) Team was established as a joint effort between the NASA Goddard Space Flight Center and the University of Texas at Austin, with collaboration from the University of Colorado and the Jet Propulsion Laboratory. During the prelaunch development and the postlaunch verification phases, the POD team improved, calibrated, and validated the precision orbit determination computer software systems. The accomplishments include (1) increased accuracy of the gravity and surface force models and (2) improved performance of both the laser ranging and Doppler tracking systems. The result of these efforts led to orbit accuracies for TOPEX/POSEIDON which are significantly better than the original mission requirement. Tests based on data fits, covariance analysis, and orbit comparisons indicate that the radial component of the TOPEX/POSEIDON spacecraft is determined, relative to the Earth's mass center, with an RMS error in the range of 3 to 4 cm RMS. This orbit accuracy, together with the near continuous dual‐frequency altimetry from this mission, provides the means to determine the ocean's dynamic topography with an unprecedented accuracy.