Abstract: Autonomous timekeeping is one of the key techniques for the autonomous navigation of navigation constellation which plays an important role in improving the viability of the navigation constellation, while the algorithm of jointed atomic time scale on board is the key of autonomous time-keeping. In this paper, both the two algorithms based on weighted average and EKF are used in the calculation of jointed atomic time scale on board. The simulation results prove that both the two algorithms can keep the clock error within 25ns in a period of 240 days.

Key words: Navigation constellation, Time scale, Autonomous time-keeping, Weighted average