# BDS Orbit Maneuver Detection Based on Epoch-Updated Orbits Estimated by SRIF
## 3 Data Processing and Validation
### Experimental Results and Verification
Figure 9: Real-time detection of the end time for orbit maneuvers. On the left-hand side is the maneuver detection for the GEO satellite C59, in the middle is the detection for the IGSO satellite C39, and on the right-hand side is the detection for the MEO satellite C24. The horizontal axis represents time in hours, and the vertical axis represents the difference between the epochs of the orbit difference, along-track difference is represented by green dots, and the cross-track difference is represented by orange dots. It is worth noting that the velocity pulses of the C39 satellite experienced jumps in two time periods. The first occurred between 07:42:00 and 07:55:00, and combined with the relatively small changes in the orbit differences shown in Figure 7, this further confirms our previous speculation that the satellite may need to adjust its attitude for the orbit maneuver. However, such an adjustment in attitude would not be reflected significantly in the orbital position, resulting in relatively small changes in orbit differences. The second jump occurred between 07:57:00 and 08:05:00. Our detection results of orbit maneuver for C39 are from 07:59:30 to 08:07:00. When compared, it was found that the start time differed by 2.5 min and the end time differed by 3 min. The verification results for the GEO satellite are presented in Figure 12.  
The results clearly indicate that the values of the velocity pulses in the along-track and cross-track directions of the satellite remained stable at below 3 mm during the non-maneuver period. These values began to gradually increase at 08:59:00, reaching a maximum value of approximately 25 mm/s at 09:00:00, and returned to a stable state at 09:01:00. In this study, the detection period was from 09:00:00 to 09:05:00. Upon comparison, it was found that the start time differed by 1 min, and the end time differed by 4 min. The reasons for this difference between detection using the orbit difference and velocity pulse are mainly due to three factors. Firstly, there were errors in the predicted orbit and SRIF-estimated orbit. Secondly, the acceleration of the orbit maneuver thrust was not immediately reflected in the GNSS distance observations, resulting in a 1-2 min delay in the start time of the detection. Thirdly, during the satellite orbit maneuver period, the initial orbit used in the SRIF estimation method was based on the predicted orbits from the previous epoch, and the low accuracy of the initial orbit during the satellite orbit maneuver period and the convergence process caused a three-minute delay in the end time compared to the velocity pulse results. Compared with the broadcast ephemeris delay time of 6-7 h, a delay of several minutes will not affect the adjustment of processing strategies for real-time  
Figure 11: The velocity pulse estimated for C38 satellite on 187 th day of 2022. Figure 12: The velocity pulse estimated for C59 satellite on 215 th day of 2022.  
and post-processed orbit determination. Additionally, these results show that the orbit maneuver period can also be detected by estimating the satellite velocity pulses, but it is impractical to estimate the velocity pulses for all epochs without knowing the approximate time period of the orbit maneuver. In addition, the start and end times of orbit maneuvering can be accurately detected in real time and post-processing using the method proposed in this paper. Subsequently, all the maneuver detection results of the BeiDou satellites in 2022 are presented in Figure 5:0  
There were 32 instances of orbit maneuvers of BeiDou satellites detected successfully in 2022. The results indicate that the orbit maneuvering frequency of GEO satellites is higher than others, occurring approximately once a month, with an average maneuvering time of around 4-5 min. The IGSO satellites have the second-highest maneuvering frequency, occurring approximately every 4-6 months, with an average maneuvering time of around 7-8 min. Only one MEO satellite, C24, was detected to be adjusted by orbit maneuvering in 2022.