# BDS Orbit Maneuver Detection Based on Epoch-Updated Orbits Estimated by SRIF
## 3 Data Processing and Validation
### Experimental Results and Verification  
In order to verify the accuracy of the orbit estimated with the SRIF method with the corresponding estimation strategy, we compared it with the GBM precise orbit product from GFZ, and the orbit accuracy is shown in Figure 5.  
It is evident from the results that, using the estimation strategy in this study, the accuracy of BeiDou MEO satellites is significantly better than IGSO and GEO satellites. The average one-dimensional accuracy of MEO satellites is 10.4 cm, while that of IGSO and GEO is 20.3 cm and 353.2 cm, respectively. After an orbit maneuver, the adjusted orbit will quickly diverge from its previous orbit [5]. So, the accuracy of the estimated orbit is sufficient for orbit maneuver detection, and this study does not discuss how to improve orbit accuracy with the SRIF estimation method. \begin{table}
\begin{tabular}{l l} \hline \hline
**Item** & **Applied Models** \\ \hline _Parameterization_ & \\ Adjustment method & SRIF. \\ Station coordinate & Tightly constrained to the IGS weekly combined solution (weekly SINEX product). \\ Receiver clocks & White noise. \\ Satellite clocks & White noise. \\ Ambiguity fixing & NO. \\ Tropospheric delay & Estimated for each station as random walk. \\ Orbit state constraints & 1d-5 km (position), 1d-6 km/s (velocity), and 1d-5 \(\upmu\)m (solar radiation pressure). \\ \hline _Dynamical models_ & \\ Earth gravity & EGM2008 up to 12 \(\times\) 12 [32]. \\ M-body gravity & Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. \\ Tidal displacement & Solid Earth, pole: IERS conventions 2010 [31]. \\ Ocean tide: FES2004 [33]. \\ Solar radiation pressure & ECOM2 + EMP [34; 35]. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
Figure 5: Orbit accuracy time series and statistical results. The left-hand side shows the time series of orbit accuracy, with the top, middle, and bottom sections corresponding to BeiDou MEO, IGSO, and GEO satellites, respectively. The blue points denote the orbit difference in along-track direction, green points denote the orbit difference in cross-track direction, and orange points denote orbit difference in radial direction; red points denote the 1D-RMS. The right-hand side displays the orbit accuracy statistical results, with the orbit accuracy of MEO, IGSO, and GEO satellites represented by blue, green, and orange bars, respectively. The results of orbit maneuver detection for GEO, IGSO, and MEO satellites are presented in this section. In Figure 6, the orbit maneuver detection results of C59 on 215 th day of 2022 are taken as an example. First, analyzing the left-hand side of Figure 6, it can be clearly seen that before 09:00:00, the orbit differences in along-track and cross-track directions were stable and had good agreement with the orbit precision in the non-maneuver period (also see Figure 4). This is due to the gradual degradation in the precision of the predicted orbit as the prediction time increased. Applying thrust to a satellite for orbit maneuvering will change its state, causing its orbit to rapidly deviate from predicted orbit. As a consequence, there was a rapid increase in the differences between the actual orbit and the predicted orbit. It was easy to detect that the C59 satellite had an orbit maneuver at 09:00:00 on the 215 th day of 2022. Due to the possibility of employing coplanar or non-coplanar orbit maneuvering, or both, an increase in the orbit difference in any direction can be regarded as an occurrence of orbit maneuvering. Orbit maneuvers can involve coplanar or non-coplanar adjustments, or both, leading to changes in the orbit in different directions [5]. Therefore, a significant increase in the orbit differences in any direction can be considered an indication of orbit maneuvering. Due to the 30 s data processing interval used in this experiment, the maneuver detection results only can be accurate to 30 s.  
Figure 6: The orbit maneuver detection for C59 satellite on 215 th day of 2022 (**upper**) and the zoom-in plots (**lower**).