Performance of the Kalman Filter of the Global Positioning System Operational Control Segment During January - March 1997
NATIONAL INST OF STANDARDS AND TECHNOLOGY BOULDER CO TIME AND FREQUENCY DIV
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We characterize the errors in the broadcast estimates of the Global Positioning Systems satellite ephemeris and clock states made by the Operational Control Segments OCS Kalman filter over the period when the system ephemeris Qs were changed. This change was called the Ephemeris Enhancement Endeavor EEE. We report on the accuracy, stability, and periodic variations of the GPS Kalman filters estimates of satellite clocks and ephemerides, particularly how they changed with EEE. Root-sum-squared RSS ephemeris error variations decreased by a factor of 1.7. The amplitude of the 2 cycled component decreased by a factor of 2.2. While the 2 cycled periodic effects dropped from 0.65 to 0.49 of the RSS ephemeris error, they still seem to be a major component. Radial ephemeris errors appear to be negatively biased by about 1 m. This bias is unchanged by EEE. Error deviations are generally no more than SV clock stabilities - the Kalman filter Qs are generally good. Clock estimate errors are worse than ephemeris errors - there may still be some room for improvement. Broadcast ephemeris errors add diurnal variations to the GPS time offset from the U. S. Naval Observatory Master Clock USNO MC. GPS - USNO MC variations for averaging times near 1 d are consistent with White PM, averaging down to 1.5 ns at 1 d with 48 pointsd. GPS - USNO MC appears to have periodic variations with periodicity spread approximately over periods from 16 to 24 d and a total amplitude of up to 4.5 ns.
- Test Facilities, Equipment and Methods
- Navigation and Guidance
- Unmanned Spacecraft