International Journal of Navigation and Observation
Volume 2008 (2008), Article ID 730284, 6 pages
doi:10.1155/2008/730284
Research Article
Backup Hydrogen Maser Steering System for Galileo Precise Timing Facility
SpectraTime, Vauseyon 29, Neuchâtel 2000, Switzerland
Received 18 July 2007; Accepted 18 November 2007
Academic Editor: Demetrios Matsakis
Copyright © 2008 Qinghua Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Two hydrogen masers (HMs) are used in the Precise Timing Facility to provide the physical realization of Galileo System Time, insuring the extremely high short-term stability required for the navigation functions. In order to allow a smooth switch over between backup and primary HMs, the “backup HM steering algorithm” is developed. This acquires the phase difference measured between two HMs, computes a steering correction, and generates the steering correction to the backup HM via a PicoStepper with a 0.1-picosecond resolution. The algorithm design is based on outlier removal and a proportional-integral filtering controller. To verify the steering operability and the loop performance, the overall backup HM steering system is simulated using real HM-HM measurements, and with simulated anomalies (phase/frequency spikes, jumps, and drift).