Abstract
The characteristics and performance of satellite clocks are important to the positioning, navigation, and timing (PNT) services of Global Navigation Satellite System (GNSS) users. Although China’s BeiDou-3 Navigation Satellite System (BDS-3) has been fully operational for more than one year, there is still a lack of comprehensive research on the onboard clocks of the entire BDS-3 constellation. In this study, the precise clock products of GeoForschungsZentrum (GFZ) from day-of-year (DOY) 1, 2021 to DOY 300, 2021 were used to analyze the characteristics and performance of BDS-3 onboard clocks from the following aspects: clock bias, frequency, drift rate, fitting residuals, periodicity, and frequency stability. Compared with BDS-2, the clock quality of BDS-3 satellites has been greatly improved, but there are still jumps in the clock offsets and frequency series of BDS-3 clocks. The drift rate of BDS-3 clocks varies within the range between −2×10−18 and 2×10−18 s/s2. The daily model fitting residuals of passive hydrogen masers (PHM) on BDS-3 medium Earth orbit (MEO), inclined geosynchronous orbit (IGSO), and geostationary (GEO) satellites are 0.15, 0.28, and 0.46 ns, respectively. The overlapping Allan deviation (OADEV) of BDS-3 MEO clocks is 4.0 × 10−14 s/s at a time interval of 1000 s. The PHMs on BDS-3 MEO satellites exhibit fewer periodic signals than those of Rb clocks. In addition, the precise clock offsets of the BDS-3 PHMs carried on the MEO, IGSO, and GEO satellites show different periodicities, which are similar to those of the corresponding types of BDS-2 satellites.
Highlights
Satellite time in the Global Navigation Satellite System (GNSS) system is established and maintained by satellite onboard clocks, and the performance of satellite clocks directly determines the accuracy of navigation, positioning, and timing services
Its satellite constellation consists of seven inclined geosynchronous orbit (IGSO), five geostationary (GEO), and three medium Earth orbit (MEO) satellites [3]
The comparison between BeiDou-3 Navigation Satellite System (BDS-3) passive hydrogen masers (PHM) and Rb clocks shows that the performance of PHMs is significantly better than Rb clocks
Summary
Satellite time in the GNSS system is established and maintained by satellite onboard clocks, and the performance of satellite clocks directly determines the accuracy of navigation, positioning, and timing services. The performance evaluation of satellite onboard clocks is of great significance to GNSS system construction and user service [1]. China’s BeiDou-2 Navigation Satellite System (BDS-2) has officially provided services to the Asia–Pacific region since 2012 [2]. Its satellite constellation consists of seven inclined geosynchronous orbit (IGSO), five geostationary (GEO), and three medium Earth orbit (MEO) satellites [3]. All of the BDS-2 satellites are manufactured by the China Academy of Space Technology (CAST). Each satellite is equipped with four high-quality rubidium (Rb) clocks [4]. Performance of BDS-2 onboard clocks has been widely studied. The clock model fitting accuracy is about 0.4 ns [5], which is worse than that of GPS satellites [6]
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