Foreword. Preface. Acknowledgments. Chapter 1. Introduction. Chapter 2. Earth-Based Tracking and Navigation Overview. Chapter 3. Range and Doppler Tracking Observables. Chapter 4. VLBI Tracking Observables. Chapter 5. Future Directions in Radiometric Tracking. Glossary. Acronyms.

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Radiometric Tracking Techniques for Deep-Space Navigation

We have conducted several time-transfer experiments using the phase of the GPS carrier rather than the code, as is done in current GPS-based time-transfer systems. Atomic clocks were connected to geodetic GPS receivers; we then used the GPS carrier-phase observations to estimate relative clock behavior at 6-minute intervals. GPS carrier-phase time transfer is more than an order of magnitude more precise than GPS common view time transfer and agrees, within the experimental uncertainty, with two-way satellite time-transfer measurements for a 2400 km baseline. GPS carrier-phase time transfer has a stability of 100 ps, which translates into a frequency uncertainty of about two parts in 10/sup -15/ for an average time of 1 day.

Carrier-phase time transfer

We have conducted global positioning system (GPS) carrier-phase time-transfer experiments between the master clock (MC) at the U.S. Naval Observatory (USNO) in Washington, DC and the alternate master clock (AMC) at Schriever Air Force Base near Colorado Springs, Colorado. These clocks are also monitored on an hourly basis with two-way satellite time-transfer (TWSTT) measurements. We compared the performance of the GPS carrier phase and TWSTT systems over a 236-d period. Because of power problems and data outages during the carrier-phase experiment, the longest continuous time span is 96 d. The data from this period show agreement with TWSTT within /spl plusmn/1 ns, apart from an overall constant time offset (caused by unknown delays in the GPS hardware at both ends). For averaging times of a day, the carrier-phase and TWSTT systems have a frequency uncertainty of 2.5 and 5.5 parts in 10/sup 15/, respectively.

Assessment of GPS carrier-phase stability for time-transfer applications

An absolute calibration technique is developed for geodetic Global Positioning System (GPS) receivers. An uncertainty budget for the system (receiver, cables, connectors, antenna) is evaluated, yielding 1.1 ns at each frequency, arid 1.6 ms for a two-receiver experiment. Analysis of data on a short baseline yields 0.8 and 1.2 ns agreement on P1 and P2, respectively.

Absolute calibration of a geodetic time transfer system

We have conducted several time-transfer experiments using the phase of the GPS carrier rather than the code as is done in current GPS based time-transfer systems. We connected atomic clocks to geodetic GPS receivers. We then used the GPS carrier-phase observations to estimate relative clock behavior at 6 minute intervals. GPS carrier-phase time transfer is more than an order of magnitude more precise than GPS common-view time transfer, and agrees within error with two-way time-transfer measurements. GPS carrier-phase time-transfer has an uncertainty of 100 psec and a frequency uncertainty of 2 parts in 10/sup 15/ for averaging times of a day.

/pdf/time-transfer-using-the-phase-of-the-gps-carrier-4pqrw0805o.pdf

Time transfer using the phase of the GPS carrier

This paper describes tests of precision GPS time transfer using geodetic-quality TurboRogue receivers. The GPS data are processed with the GIPSY-OASIS II software, which simultaneously estimates the GPS satellite orbits and clocks, receiver locations and clock offsets, as well as other parameters such as Earth orientation. This GPS solution technique, which emphasizes high accuracy GPS orbit determination and observable modeling, has been shown to enable sub-1 ns time transfer at global distance scales. GPS-based monitoring of clock performance has been carried out for several years through JPL's high precision GPS global network processing. The paper discusses measurements of variations in relative clock offsets down to a level of a few tens of picoseconds. GPS-based clock frequency measurements are also presented.

S.M. Lichten

Papers

A test of precision GPS clock synchronization