NRL analysis of GPS on-orbit clocks

The U.S. Naval Research Laboratory (NRL) has collected data and analyzed GPS space vehicle atomic clock performance since the beginning of the GPS Program. These analyses have largely been based on pseudorange observations and precise post-fit ephemerides provided by the National Geospatial-Intelligence Agency (NGA). Observational data and clock comparisons were limited to data collected within the GPS system due primarily to the lack of global tracking resources and effective means of gathering the data. With the successful conclusion of the International GPS Service (IGS) and Bureau International Poids and et Mesures (BIPM) Pilot Project, new capabilities to associate IGS geophysical data to universal coordinated time (UTC), and integration of timing centers to contribute to the determination of UTC are evolving. Data collection from participating timing centers and analysis to form the IGS timescales and Clock Products has established new capabilities for analysis of orbiting precision atomic clocks. NRL leads the IGS Clock Products Working Group and generates the IGS timescales. These efforts joined together with the GPS on-orbit analyses offer new possibilities for analysis and improved performance for both GPS and IGS. This paper discusses these new resources for analysis and possible improved analytical capabilities