# BDS Orbit Maneuver Detection Based on Epoch-Updated Orbits Estimated by SRIF
## 4 Conclusions and Discussion  
This study proposes a real-time and post-processing detection method for orbit maneuvering of BeiDou satellites. Based on the SRIF estimation method, the correct orbit of the maneuvering satellite can be correctly estimated and compared with the forward- and backward-predicted orbits according to the precise orbit before and after the maneuver. This method can accurately detect the start and end time of the orbit maneuvers, and can also achieve maneuvering start time detection in real time. In addition, we propose a real-time detection method for the end time of orbit maneuvering, based on the state difference during maneuver and non-maneuver periods. By analyzing the epoch-to-epoch variation in orbit differences, the end time of orbit maneuvers can be detected in real time.  
Our experimental analysis validates the correctness of the proposed method. There were 32 instances of orbit maneuvers of BeiDou satellites detected successfully in 2022. The maneuvering frequency of BeiDou GEO satellites is once a month, with an average maneuvering time of 4-5 min, while the frequency of IGSO satellites is 4-6 months, with an average maneuvering time of 7-8 min. This method is applicable to satellites of all orbit types of GNSS, including GEO, IGSO, and MEO satellites.  
Moreover, the method is easily implemented for all common users and data used can be accessed easily, including GNSS observation data, broadcast ephemeris, and other open-source information files. The results of orbit maneuver detection are crucial in precise orbit determination in real-time and post-processing. They provide critical information for adjusting precise orbit determination strategies, further improving the continuity and reliability of precise service products of the BDS, thereby further enhancing the PNT service performance of the BeiDou Navigation System.  
This method also has some limitations. As our proposed approach requires precise orbit products from the day before and after the orbit maneuver, the detection of a satellite with continuous two-day maneuver adjustments will fail. On the other hand, it is also limited by the accuracy of the estimated orbit, resulting in a delay of several minutes in the detection results. The orbit constraints also need further investigation. When the constraint is too tight, the system error caused by the orbit maneuver acceleration cannot be fully absorbed. Conversely, the loose constraints make the orbit accuracy poor. In addition, the situation of multiple maneuvers may occur in the same day, and the real-time method performs worse than the post-processing method. These questions need to be addressed in future studies.  
Conceptualization, Z.Q. and Q.Z.; methodology, Z.Q. and G.H.; software, Z.Q. and L.T.; validation, Z.Q., L.T. and J.W.; writing--original draft preparation, Z.Q. and Q.Z.; writing--review and editing, J.W., G.H. and X.W.; supervision, Q.Z. All authors have read and agreed to the published version of the manuscript.  
This work was supported by Fundamental Research Funds for the Central Universities, CHD (300102260707), Chinese Scholarship Council studentship (ref. 202006560033), Programs of the National Natural Science Foundation of China (42127802), and the Key R&D Program of Shaanxi Province (2022 ZDLSF07-12).  
The authors would like to thank GFZ for the computer equipment and iGMAS, MGEX, and IGS for data support.  
The authors declare no conflict of interest.