## 4 Maneuver Assessment and POD Results  
### Maneuver Assessment by POD  
Without proper maneuver handling, the quality of the POD results will degrade around the thrust execution times. Therefore, the performance of the maneuver handling is important for the orbit precision of the satellites. Here, we adopt the residuals of the POD to reflect the influence of thrusts to the orbit accuracy. It may be noted that the ionosphere-free carrier phase linear combination (LC) residuals of the GPS-based POD \begin{table}
\begin{tabular}{c c} \hline \hline
**Models** & **Description** \\ \hline \hline Observation models & \\ \hline Observation & Undifferenced ionosphere-free pseudorange and carrier phase; \\ Weight & A priori sigma 2 m for the pseudorange and 0.5 cm for the carrier phase observations, \\ Orbit arc length/Interval & with function 2 sin(\(\theta\)) when the elevation angle \(\theta\) is below 30\({}^{\circ}\); \\ GNSS ephemeris and clock & GeoForschungsZentrum (GFZ) products [38]; \\ GPS satellite PCO/PCV & igs14_2062.txt [39]; \\ BDS2 satellite PCO/PCV & Models from the European Space Agency (ESA) [40]; \\ Receiver antenna PCO & Nominal values; \\ Receiver antenna PCV & In-flight estimated PCV maps; \\ LEO attitude & Star tracker data; \\ Antenna phase windup & Phase wind-up correction [41]; \\ DCB correction & Chinese Academy of Sciences (CAS) multi-GNSS differential code biases (DCB) \\  & products [42]; \\ \hline Dynamical models & \\ \hline Gravity field & GGM05S(120 \(\times\) 120) [43]; \\ Solid-earth, pole, and ocean tides & IERS 2010 [44]; \\ Third body gravity & Luni-solar-planetary gravity [45]; \\ Relativity & Only the Schwarzschild item; \\ Atmospheric drag & Jacchia 71 density model [46], one drag coefficient per 3 h; \\ Solar radiation pressure & Cannonball model, one solar radiation coefficient per 30 h; \\ Empirical acceleration & Constant accelerations in radial direction; piecewise linear accelerations at 15 min \\  & interval in along-track and normal directions; \\ Maneuver acceleration & Constant thrust model over predefined maneuver durations. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Processing strategy for the POD of TH-2. for the TH-2A without the maneuver estimation are larger than those with the maneuver estimation around the thrust execution periods, as shown in Figure 8.  
Since the inclusion of the observations from the BDS2 GEOs have a negative influence on the POD precision of LEOs [47; 48], only the observations from the MEOs and IGSOs are used in the BDS2-based POD. Since the number of available BDS2 observations is smaller than the GPS, the minimum number of available navigation satellites per epoch is set to two instead of three in the BDS2-based POD. Figure 9 shows the LC residuals of the BDS2-based POD for the TH-2A with and without maneuver estimation. Periodic gaps can be noticed in the BDS2 LC residuals because there is only zero to one available satellite at these epochs. If there is no maneuver handling, the LC residuals during the thrust execution periods are apparently larger than those at other epochs. On the contrary, the significant fluctuations of the residuals around the maneuver thrusts are removed when the maneuver handling is taken into account. Table 2 shows the average RMS of the residuals for the GPS- and BDS2-based POD. It can be found that the LC residuals for the POD with maneuver estimation are significantly  
Figure 8: LC residuals of GPS-based POD for TH-2A without maneuver estimation (**top panel**) and those with maneuver estimation (**bottom panel**) on DOY 314, 2019. The vertical bars denote the centers of the thrust execution periods. Residuals beyond \(\pm\)6 cm are not shown in the top panel. Figure 9: LC residuals of BDS2-based POD for TH-2A without maneuver estimation (**top panel**) and those with maneuver estimation (**bottom panel**) on DOY 314, 2019. The vertical bars denote the centers of thrust execution periods. Residuals beyond \(\pm\)6 cm are not shown in the top panel.