Performance Evaluation of BDS-3 Spaceborne Atomic Clock Using Different Time Synchronization Systems

  Objectives  The performance of the global navigation satellite system (GNSS) spaceborne atomic clock affects the entire navigation system, by having direct impact on GNSS measurement quality, ranging precision, clock prediction and satellite autonomous navigation capabilities. Different time synchronization systems may have different impact on the evaluation of spaceborne atomic clock. Precise clock bias data determined by inter-satellite link (ISL), two-way time transfer (TWTT) and orbit determination and time synchronization (ODTS) system are used to further evaluate the performance of BeiDou-3 on-orbit atomic clock.

  Methods  Quadratic polynomial model and total Allan / Hadamard variance are used to analyze the performance of the BeiDou-3 navigation satellite system (BDS-3) satellite clock data of the three different time synchronization systems.

  Results  The result shows that the frequency accuracy and frequency drift of the above three clock bias determination systems are consistent. The frequency accuracy of all satellites is within the range of (-4~2)×10^-11. Frequency accuracy of hydrogen clock is better than that of rubidium clock. The frequency drift based on the ISL system is slightly better than that of the ODTS, the three clock determination systems have their own advantages in evaluating the stability of the atomic clock, respectively. For short-term stability, the ODTS whose 3 000 s stability reaches 3×10^-14 is better than that of ISL, and hydrogen clock is better than rubidium clock. For medium-term and long-term stability, when the averaging time is greater than 1×10⁴ s, the result of ISL is closer to the actual condition of the BDS-3 spaceborne clock. For long-term stability more than 7 days, the broadcast ephemeris bias based on TWTT system can be used for rapid evaluation, which result is close to ODTS and ISL.

  Conclusions  The three clock bias determination systems can be used to evaluate the frequency accuracy and frequency drift of on-orbit atomic clocks with basically consistent statistical results. The three clock bias determination systems have their own advantages in assessing the stability of the orbiting satellite clock when selecting different averaging time.