Empirical Studies Into GPS Extended Navigation Performance

Christopher M. Shank, Keith Melkun

Abstract:	The GPS Master Control Station (MCS) produces navigation data predictions up to 180 days into the future based upon current MCS Kalman filter estimates of satellite states (position, velocity, solar. and clock). These predictions are then formatted into subfrarne data to be uploaded into each satellite on a daily basis or so that each satellite’s predicted ephemeris and clock deviations will not exceed 10 meters difference from the last navigation upload to the current MCS Kalman estimate. This does not account for unmodeled errors invisible to the Kalman falter which account for an additional 1-2 meters of error, nor the effects of Selective Availability to the SPS user. GPS system operating requirements specify that estimated range errors from individual satellites will not exceed 6 meters (one-sigma) when the age of the navigation data is less than 10 hours old, less than 200 meters (one-sigma) when the age of data is less than 14 days old, and less than 10,000 meters (one- sigma) when the data is less than 180 days old. This study will present MCS navigation predictions generated through the first 14 and 180 days into the future compared against precise ephemerides collected during the same 14 and 180 day periods from the National Geodectic Survey (NGS). The errors are attributed to prediction and fitting errors. Space segment perturbations cause large deviations over the long-term if the satellite’s navigation upload data is not updated with the most recent Kalman filter estimate. As the MCS provides the best prediction capability for GPS satellite orbits, several programs may be interested in using this predicted information for their applications and should know the performance characteris tics of the navigation upload data. These predictions are not available as public domain. Only the broadcast navigation data is available, but this data could be made available in the future on a case-by-case basis.
Published in:	Proceedings of the 50th Annual Meeting of The Institute of Navigation (1994) June 6 - 8, 1994 Antlers Doubletree Hotel Colorado Springs, CO
Pages:	483 - 488
Cite this article:	Shank, Christopher M., Melkun, Keith, "Empirical Studies Into GPS Extended Navigation Performance," Proceedings of the 50th Annual Meeting of The Institute of Navigation (1994), Colorado Springs, CO, June 1994, pp. 483-488.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In