Performance Evaluation of GPS in-orbit Satellite Clocks
LEI Yu1,ZHAO Dan-ning2
1. School of Computer Science & Technology,Xi’an University of Posts & Telecommunications, Xi’an, Shaanxi 710121, China
2. School of Electrical & Electronic Engineering, Baoji University of Arts and Sciences, Baoji, Shaanxi 721016, China
Abstract It plays an key role in system integrity monitoring and satellite clock prediction to evaluate the performance of satellite clocks in orbit. The work is aimed at evaluating the performance of the on-board clocks in the GPS Block IIR, IIR-M, IIF and newest Block IIIA satellites. The final precise GPS satellite clock produces from the International GNSS Service (IGS) are used to calculate the four indexes, namely the frequency accuracy, drift, stability for an average time of ten thousand seconds as well as stability for a 1-day average time. The results show that the magnitudes of frequency accuracy and drift reach the 10-13～10-12 and 10-15～10-14/d level, respectively. As for frequency stability, the in-orbit Rubidium clocks stability for an average time of ten thousand seconds and one day can reach a magnitude at the 10-14 and 10-15 level, respectively. It is illustrated that the stability of the in-orbit Rubidium clocks is noticeably higher than that of the cesium clocks by an order of magnitude both for the short-and long-term average time. The frequency accuracy and drift of the Block IIIA satellite clocks are comparable with those of the other clocks. However, the frequency stability for an one day interval is at a (3～5)×10-15 level and therefore higher than that of the existing satellite clocks in orbit, demonstrating that the on-board clocks equipped in the newest Block IIIA satellite are continually optimized and improved. In addition, It is found that even for the same Block satellites there are certain performance differences between the on-board clocks, which has no significant relationship with the operation time of the satellite clocks in flight.
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2022, Vol. 43 
