A Space-Based Autonomous Timekeeping Method Based on Onboard Atomic Clocks and Inter-Satellite Measurements.

Area of Science:

• Satellite Navigation Systems
• Timekeeping and Metrology
• Aerospace Engineering

Background:

• Global Navigation Satellite Systems (GNSS) traditionally rely on ground control for time reference, ensuring UTC traceability and interoperability.
• Advances in atomic clock stability and inter-satellite time transfer (ISL) enable autonomous space-based timekeeping.
• The BeiDou-3 (BDS-3) system features high-performance hydrogen masers and Ka-band ISL, crucial for precise time transfer.

Purpose of the Study:

• To propose and validate a space-based autonomous timekeeping approach for GNSS constellations.
• To enhance the resilience and reliability of GNSS time maintenance, especially during ground disruptions.
• To generate accurate satellite clock offset predictions for improved navigation services.

Main Methods:

• Developed a space-based autonomous timekeeping strategy combining high-precision ISL synchronization with a hydrogen maser ensemble.
• Implemented a space-ground cooperative strategy to steer the space-based timescale (TA(SPACE)) to the BeiDou Time (BDT).
• Utilized in-orbit BDS-3 clock offset data for performance evaluation and clock parameter product generation.

Main Results:

• In autonomous mode, the time offset between TA(SPACE) and BDT was maintained within 25.06 ± 41.47 ns over 90 days.
• In space-ground cooperative mode, satellite-ground steering stabilized the offset to within 10 ns.
• The approach demonstrated practical feasibility for constellation time maintenance under various conditions.

Conclusions:

• The proposed space-based timekeeping approach offers a resilient solution for GNSS time maintenance.
• Autonomous and cooperative strategies significantly improve time stability and reliability.
• This advancement enhances the overall robustness and dependability of global navigation satellite services.