Research on Constellation Autonomous Timekeeping Algorithm Based on Inter-satellite Link

At present, the system time reference of the global satellite navigation system mainly relies on the establishment and maintenance of the ground operation and control system. If the ground operation control system fails or the satellite-ground link is interrupted, the satellite is unable to measure its timing deviation relative to the system’s reference clock, the time reference of the navigation satellites may gradually deviate from the navigation system time in autonomous operation mode. Therefore, it is necessary to establish an satellite-onboard time reference that can satisfy the autonomous operation of the constellation. Based on the Beidou inter-satellite link, the research on the constellation autonomous timekeeping method is carried out. Using the computed relative clock offset from the inter-satellite link as the input, a comprehensive time scale whose frequency stability is better than any single satellite-borne clock is generated through the constellation autonomous timekeeping comprehensive time scale algorithm, the day stability is $4.24 \mathrm{E}-15$. The satellite operates autonomously for $\mathbf{3 0}$ days, the timing offset between the satellite’s internal clock and the ideal time reference is kept within 30 ns, it is far superior to the timekeeping ability of a single satellite-borne clock.