GPS Monitor Station Upgrade Program at the Naval Research Laboratory

Abstract

One of the measurements made by the GPS Monitor Stations is to measure the continuous pseudorange of all the passing GPS satellites. The pseudo-range contains GPS satellite and Monitor Station clock errors as well as GPS satellite navigation errors. Currently the time at the GPS Monitor Station is obtained from the GPS constellation and has an inherent inaccuracy as a result. Improved timing accuracy at the GPS Monitor Stations will improve GPS performance. The U.S. Naval Research Laboratory (NRL) is developing hardware and software for the GPS Monitor Station Upgrade program to improve the Monitor Station clock accuracy. This upgrade will allow a method independent of he GPS satellite constellation of measuring and correcting Monitor Station time to US. Naval Observatory (USNO). The hardware consists of a high-performance atomic cesium frequency standard (CFS) and a computer which is used to ensemble this CFS with the two CFSs currently located at the Monitor Station by use of a dual-mixer system. The dual-mixer system achieves phase measurements between the high-performance CFS and the existing Monitor Station CFSs to within 400 femtoseconds. Time transfer between USNO and a given Monitor Station is achieved via a two-way satellite time transfer modem. The computer at the Monitor Station disciplines the CFS based on a comparison of one pulse per second sent from the master site at USNO. The Monitor Station computer is also used to perform housekeeping functions, as well as recording the health status of all three CFSs. This information is sent to USNO through the time-transfer modem. Laboratory time synchronization results in the sub-nanosecond range have been observed and the ability to maintain the Monitor Station CFS frequency to within 3.0 x 10 (exp -14) of the master site at USNO.

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Document Details

Document Type
Technical Report
Publication Date
Dec 01, 1995
Accession Number
ADA501989

Entities

People

  • Dwin M. Craig
  • Ivan J. Galysh

Organizations

  • United States Naval Research Laboratory

Tags

Communities of Interest

  • Space

DTIC Thesaurus Topics

  • Accuracy
  • Algorithms
  • Artificial Satellites
  • Clocks
  • Computers
  • Frequency
  • Frequency Standards
  • Global Positioning Systems
  • Measurement
  • Military Research
  • Operating Systems
  • Phase Measurement
  • Satellite Constellations
  • Spacecraft
  • Standards
  • Test And Evaluation
  • Time Intervals

Fields of Study

  • Physics

Readers

  • Positioning, Navigation, and Timing (PNT) Technology.

Technology Areas

  • Space
  • Space - Satellites