Architecture and Algorithm Design of Navigation Satellite Robust Ensemble Clock System

The application of the new type of Atomic Frequency Standard (AFS) and the onboard clock ensemble technology is the evolution trend to realize the high precision and stability of space-based time reference establishment and maintenance for next-generation global navigation satellite systems (GNSS). The architecture upgrade with ensemble clock group management mode provides the on-orbit continuous direct measurement and autonomous fault detection and recovery of the AFS group. This research proposes a framework for the GNSS robust heterogeneous ensemble clock system that includes the two-stage Kalman filter logic structure. For the application scenario of single satellite resilient ensemble time-scale (ETS) generation, a resilient Kalman plus weights (KPW) time-scale algorithm considering dynamic weight factors is designed, and its robustness against clock outages and anomalies is analyzed when using multiple heterogeneous AFS configuration presets. Then, an intuitive and practical strategy of control parameter determination is introduced to support the linear quadratic Gaussian (LQG) control model to generate appropriate control inputs for optimal frequency steering. The simulation results show that the spaceborne composite clock signal combines the advantages of short- and long-term frequency stability and improves the overall stability performance compared with a single AFS. The long-term stability of the designed primary timekeeping satellite node can reach 4.68E-16/1 day and 5.71E-16/1 day, respectively, when adopting two heterogeneous AFS configurations. The research results are expected to be applied to the next-generation GNSS spaceborne time–frequency system development and improve the operational robustness and autonomous timekeeping capacity of the ensemble clock group.