The time maintenance accuracy of the navigation constellation determines the user positioning and timing performance. Especially in autonomous operation scenarios, the performance of navigation constellation maintenance time directly affects the duration of constellation autonomous navigation. Among them, the frequency stability of the atomic clock onboard the navigation satellite is a key factor. In order to further improve the stability of the navigation constellation time-frequency system, combined with the development of high-precision inter-satellite link measurement technology, the idea of constructing constellation-level synthetic atomic time has gradually become the development trend of major GNSS systems. This paper gives a navigation constellation time scale generation framework, and designs an improved Kalman plus weights (KPW) time scale algorithm and time-frequency steer algorithm that integrates genetic algorithms. Finally, a 30-day autonomous timekeeping simulation was carried out using the GPS precision clock data provided by CODE, when the sampling interval is 300 s, the Allan deviation of the output time scale is 5.73 × 10⁻¹⁴, a 71% improvement compared with the traditional KPW time scale algorithm; when the sampling interval is 1 day, the Allan deviation is 9.17 × 10⁻¹⁵; when the sampling interval is 1 × 10⁶ s, the Allan deviation is 8.87 × 10⁻¹⁶, a 94% improvement compared with the traditional KPW time scale algorithm. The constellation-level high-precision time scale generation technology proposed in this paper can significantly improve the stability performance of navigation constellation autonomous timekeeping.

The application of the new type Atomic Frequency Standard (AFS) and the onboard clock ensemble technology is the evolution trend to realize the high precision and stability space-based time reference establishment and maintenance for next-generation Global Navigation Satellite System (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 of the GNSS robust heterogeneous ensemble clock system which 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-16/1day and 5.71E-16/1day 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.