Optimal Time Transfer

Abstract

We have designed an optimal time transfer algorithm using GPS carrier-phase and pseudorange measurements. This will enable the near-real-time estimation of the difference between the phase of a stable real-time UTC ground clock attached to a GPS ground receiver and the phase of each NAVSTAR spacecraft clock in the ensemble of GPS spacecraft. We propose a master filter (MF) to drive multiple instances of spawned filters (SF) and fixed-epoch smoothers (FES). The MF is designed to map all GPS carrier-phase measurement information of each GPS ground-station/NAVSTAR pass into the complete MF state estimate of all NAVSTAR parameters and all station parameters, with all serial correlations and all cross-correlations accounted for. Each SF runs forward with time while the FES linearly maps measurement information backwards to fixed epochs for individual NAVSTAR spacecraft. FES estimates are then folded into the MF as pseudo-measurements. The resulting time-transfer algorithm is an autonomous forward-running sequential estimator, with no state-sized matrix inverse calculations required.

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Document Details

Document Type
Technical Report
Publication Date
Nov 01, 2009
Accession Number
ADA517832

Entities

People

  • James R. Wright
  • James Woodburn

Tags

Communities of Interest

  • Space

DTIC Thesaurus Topics

  • Algorithms
  • Clocks
  • Coordinate Systems
  • Covariance
  • Cross Correlation
  • Estimators
  • Filters
  • Ground Stations
  • Intervals
  • Kalman Filters
  • Measurement
  • Noise
  • Numbers
  • Phase Measurement
  • Three Dimensional
  • Time Intervals
  • White Noise

Fields of Study

  • Physics

Readers

  • Adaptive Control and Estimation with Uncertainty in Dynamic Systems.
  • Positioning, Navigation, and Timing (PNT) Technology.

Technology Areas

  • Space
  • Space - Spacecraft Maneuvers