# BDS Orbit Maneuver Detection Based on Epoch-Updated Orbits Estimated by SRIF
## 3 Data Processing and Validation
### Experimental Results and Verification
The vertical axis denotes the orbit difference between the SRIF-method-estimated orbit and the predicted orbit according to the orbit parameters estimated using batch least squares, measured in dm units. On the left-hand side are the orbit differences between the estimated orbit and the forward-predicted orbit using the precise orbit from previous day, which could be used for detecting the orbit maneuvering start time. On the right-hand side are the orbit differences between the estimated orbit and the backward-predicted orbit using the precise orbit from following day, which could be used for detecting the orbit maneuvering end time. The red dots represent the orbit differences in along-track direction of the C59 satellite, while the blue dots represent the orbit difference in cross-track direction. Orbit maneuvers can be divided into coplanar and non-coplanar maneuvers. Coplanar maneuvers can be reflected in orbit differences in along-track direction, while non-coplanar maneuvers can be reflected in orbit difference in cross-track direction. In addition, considering the strong coupling relationship between the orbit in radial direction and the clock offset, the orbit differences in radial direction are not used in this study. Second, it is evident from the right-hand side of Figure 6 that before 09:00:00, the orbit differences rapidly increased due to the inconsistency between the orbit estimated using the SRIF and the reverse-predicted orbit after orbit maneuvering. The orbit differences began to show a stable trend, but minor variations still persisted from 09:00:30 to 09:05:00 due to the continuation of maneuvering thrust on the satellite. The satellite remained unstable during this time and had not yet achieved a stable state. After the orbit maneuvering thrust applied to the satellite completely disappeared, the satellite returned to a stable state. Based on this characteristic, it was easy to detect that the C59 satellite returned to a stable state at 09:05:00. Therefore, the end time of the orbit maneuvering for the C59 satellite was 09:05:00 on the 215 th day of 2022. To demonstrate the applicability of this orbit maneuver detection method to IGSO and MEO satellites, the analysis results are presented in Figures 7 and 8. From Figure 7, it can be clearly seen that before 07:45:30, the orbit differences in the along-track and cross-track directions were nonzero, but they remained in a linear and stable state for a brief period. From 07:45:30 to 07:59:30, the orbit differences gradually exhibited a small upward trend. Due to the relatively small magnitude of the orbit differences, we cannot assert with certainty that they were a result of orbit maneuvers. Because different orbital types may require different adjustments for orbit maneuvering, we speculate that this phenomenon may be due to satellite attitude adjustments made in preparation for such maneuvers. However, since we have been unable to obtain official information, this remains an unconfirmed speculation. It was easy to detect that the C39 satellite had an orbit maneuver at 07:45:30 on the 181 st day of 2022. Second, it is evident from the right-hand side of Figure 7 that, before 08:07:00, the orbit differences rapidly decreased due to the inconsistency between the orbit estimated using the SRIF and the reverse-predicted orbit after orbital maneuvering. After the orbit maneuvering thrust applied to a satellite completely disappears, the satellite will be in a stable state. Based on this characteristic, it was easy to detect that the C39 satellite had returned to a stable state at 08:07:00. Therefore, the end time of the orbit maneuvering for the C39 satellite was 08:07:00 on the 181 st day of 2022. Figure 7: The orbit maneuver detection for C39 satellite on 181 st day of 2022. This is the same as Figure 6, but for a different satellite in a different day. From Figure 8, it can be clearly seen that before 07:31:00, the orbit differences in the along-track and cross-track directions remained in a linear and stable state for a brief period.