Abstract: The BDS-3 satellite is equipped with Ka-band inter-satellite link (ISL) payload to realize ranging and communication between satellites. By taking all the spaceborne atomic clocks of the constellation as a group, the clock error within the group can be measured in nearly real-time by ISL. With some of the more stable clocks as the reference, the constellation pseudo-stable atomic timescale can be established. The deviation between the constellation pseudo-stable clock and the BeiDou time (BDT) can be obtained using only one or a few ground stations. The performance of the spaceborne atomic clock and the accuracy of the clock prediction can be obtained using the pseudo-stable constellation clock errors, which avoids the influence of the satellite orbit error on the clock error estimation and can get more realistic and reliable analysis results. The results show that the spaceborne atomic clocks of the BDS-3, especially the passive hydrogen maser (PHM), have good stabilities. The average Hadamard deviation with an integration time of 1 day is 3.5E-15 for MEO satellite PHM, 2.8E-15 for IGSO satellite PHM and 8.2E-15 for MEO rubidium atomic frequency standards (RAFSs). The RMS of 1 hour prediction error of the constellation pseudo-stabilized clock bias is about 0.1 ns, which can improve the BDS-3 signal in space accuracy to even better than 15 cm. Obviously, the huge potential of ISL needs to be further explored.

Key words: BDS-3, atomic clock, inter-satellite link, pseudo-stable, frequency stability, clock bias