Spaceborne atomic clock performance review of BDS-3 MEO satellites

Abstract

Abstract On June 23, 2020, the final satellite of the third generation Beidou satellite navigation system (BDS-3) was launched, which represents the BDS-3 is fully operational and can provide global services. Due to the fact that BDS-3 constellation mainly consists of Medium Earth Orbit (MEO) satellites, we only discussed the in-orbit atomic clock performance of MEO, and compared to that of the latest generation of GPS as well as Galileo satellites. Based on the precise satellite clock product provided by German Research Center for Geosciences (GFZ), a level of 0.2\xa0ns fitting precision is obtained, and it is better than BDS-2. The periodic terms of satellite clock are analyzed by means of spectrum analysis. Except some mutual periodic terms, several exclusive periodic terms, approximately 8\xa0h, 6\xa0h and 4.8\xa0h harmonics, are found in passive hydrogen masers (PHMs) of BDS-3, and possible reasons are given. Clock systematic characteristics, such as frequency accuracy and drift rate are examined and found that PHMs have better result than rubidium atomic clocks. Finally, frequency stability is evaluated: all BDS-3 satellite clocks can reach the order of 10-15 at the average interval of 86400\xa0s, which is much better than BDS-2 and comparable to the latest type of GPS III as well as Galileo satellites.