Abstract
The BeiDou Navigation Satellite System (BDS) is essentially a precise time measurement and time synchronization system for a large-scale space near the Earth. General relativity is the basic theoretical framework for the information processing in the master control station of BDS. Having introduced the basic conceptions of relativistic space–time reference systems, the space–time references of BDS are analyzed and the function and acquisition method of the Earth Orientation Parameters (EOP) are briefly discussed. The basic space reference of BDS is BeiDou Coordinate System (BDCS), and the time standard is the BDS Time (BDT). BDCS and BDT are the realizations of the Geocentric Terrestrial Reference System (GTRS) and the Terrestrial Time (TT) for BDS, respectively. The station coordinates in the BDCS are consistent with those in International Terrestrial Reference Frame (ITRF)2014 at the cm–level and the difference in scale is about 1.1 times 10^{ - 8}. The time deviation of BDT relative to International Atomic Time (TAI) is less than 50 ns and the frequency deviation is less than 2 times 10^{ - 14}. The Geocentric Celestial Reference System (GCRS) and the solar Barycentric Celestial Reference System (BCRS) are also involved in the operation of BDS. The observation models for time synchronization and precise orbit determination are established within the GCRS framework. The coordinate transformation between BDCS and GCRS is consistent with the International Earth Rotation and Reference Systems Service (IERS). In the autonomous operation mode without the support of the ground master control station, Earth Orientation Parameters (EOP) is obtained by means of long-term prediction and on-board observation. The observation models for the on-board astrometry should be established within the BCRS framework.
Highlights
Since July 31, 2020, BeiDou-3 Navigation Satellite System (BDS-3) has been officially operational
The joint calculation method of satellite orbit and satellite clock offset is adopted by Global Positioning System (GPS) and Galileo Navigation Satellite System (Galileo), which will result in a strong correlation between the derived satellite orbit and satellite clock offset (Demetrios et al, 2008)
The International Terrestrial Reference System (ITRS) maintained by International Earth Rotation and Reference Systems Service (IERS) is an implementation of Geocentric Terrestrial Reference System (GTRS), which constitutes a set of prescriptions and conventions together with the modeling required to define the origin, scale, orientation, and time evolution
Summary
Since July 31, 2020, BeiDou-3 Navigation Satellite System (BDS-3) has been officially operational. With the daily frequency stability of the BDS satellite atomic clock at the level of 1 × 10−15 , the time synchronization uncertainty is required to reach 1 ns or even higher, and the accuracy of the space–time measurement and observation model is required to reach the order of picosecond (Han and Cai 2019). Local inertial reference system According to the principle of equivalence of relativity, for any mass point as an observer that moves freely in space– time, an inertial space reference frame or a local inertial reference system that is applicable to the observer local space–time can be constructed.
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