Observable Relativistic Frequency Steps Induced by GPS Orbit Changes; Conference paper

摘要

A study by ITT Industries of GPS Block IIR clock performance history during 2000 revealed a relativistic association between the observed frequency steps and changes in orbit. This paper presents the GPS IIR clock's observed performance during minor orbital perturbations that were made to enhance navigation coverage; analysis of the results; and the conclusion drawn on a relativistic association between clock performance and orbital changes. Frequency steps accompanied orbit changes. Although the frequency steps were detected by GPS clock monitoring, they were not associated with the orbit changes by the observers. The association was not obvious because the relativistic frequency shifts were obscured by nearby clock system adjustments, which essentially zeroed the phase, frequency, and drift error of the SVN43 clock. Our preliminary analysis of clock data from SVN43 from 18 June 2000 through 31 December 2000 indicated that the Time Keeping System's observed performance differed from what we had predicted for GPS IIR. ITT initiated a relativity study of the observed frequency step and the change in orbit. We examined the orbits before and after the orbit change. The difference in average velocity between the two orbits was 1.3 meters per second. Then we predicted the frequency step using the orbit change and relativity calculations. We found that the application of traditional relativity formulas predicted the observed frequency with an error of less than 4.5%. ITT confirmed the relativistic effect by studying the orbit change of GPS IIR satellite SVN54 on 9 March 2001. In this case as well, there was a close match between the observed frequency and the rercltivity prediction. We conclude that GPS orbit shifts can generate significant clock frequency shifts due to relativistic phenomena. Knowledge of this effect can be used to produce better tracking of the satellites and their clocks in the vicinity of orbit changes.