# Precise Orbit Determination for GNSS Maneuvering Satellite with the Constraint of a Predicted Clock
## 3 Experiment Analysis
### Test on the Real Maneuver Cases  
The proposed method is further validated by the actual maneuver cases of GPS and BDS satellites. Figure 6 illustrates the POD processing scheme for the maneuvering satellites. As shown in this  
Figure 5: Orbit differences between the RPPP and dynamic POD solutions for GPS and BDS satellites ((a): Orbit differences for GPS satellites; (b): Orbit differences for BDS satellites; **left**: RPPP without clock-constraint, **right**: RPPP with clock-constraint). figure, after the maneuver time is roughly detected using the method proposed by [PERSON] et al. (2019), we divide the whole 48-h orbit arc into two parts: the normal orbit arc without maneuvers and the 2-h maneuvering orbit arc covering the whole maneuver events. The dynamic POD method is employed with the last 2-h observations of maneuvering satellites excluded to generate precise receiver positions, receiver clocks, ZTDs, ambiguities and IFBs. Then, the clock-constrained RPPP is carried out for the maneuvering satellites within the last 2 h. Since the reference orbits are not available during maneuvering, to evaluate the orbit precision during the maneuvering periods, the clock-constrained RPPP solution is compared with the forward and backward integration orbits based on the dynamic POD estimation before and after maneuvering, respectively. Furthermore, the forward and backward RPPP POD solutions are also compared to validate the accuracy of this method. Figure 7 shows the orbit differences between the clock-constrained RPPP solution and the forward and backward integration orbits in the radial, cross-track and along-track directions for G12, G22, C02 and C04 satellites. It is necessary to mention that, the C04 satellites experiences another maneuver about 25 h later after the illustrated one. Thus, the backward POD arc of C04 is set to 24 h to avoid the maneuvering observations, which degrades the dynamic POD precision heavily and introduces significant biases in the orbit differences ([PERSON], 2016). Additionally, the C04 maneuver period is a little longer than the others, so we set the maneuver processing arc to 3 h to include the whole maneuver event. The vertical dashed lines indicate the detected start and end time of maneuver events. As shown in this figure, the orbit differences of GPS satellites are less than 20 cm in all the three directions during the normal orbit arcs, which increase rapidly when the satellites are experiencing maneuvers. The extreme enlargements in GPS orbit differences during maneuvering periods can be attributed to the un-modeled maneuver thrust in the dynamic orbit integration. Similarly, the orbit differences of BDS satellites during the normal orbit arcs are less than 30 cm in the radial and cross-track directions and less than 150 cm in the along-track direction, which are much smaller than those during maneuvering periods. Furthermore, because the BDS dynamic models are not as accurate as that of GPS, the fixed parameters in RPPP processing, which are estimated from the dynamic POD before maneuvers, are not well consistent with the parameters estimated from the backward integration orbits, resulting in the discrepancy in the orbit differences before and after maneuvering. We can find that the BDS orbit differences experience three stages during maneuvering periods: gradual changes at the beginning and end stages and rapid changes at the middle stages, which have not been found in GPS orbit differences. In addition, the duration of orbit maneuver for GPS satellites is much shorter than BDS satellites. Figure 6: Computation and comparison strategy for the maneuvering satellites. Table 3 presents the detected maneuver time and the unhealthy epochs in broadcast ephemeris for all maneuvering satellites during the experiment period. The maneuver duration of GPS satellites is less than 2 min, while that of BDS satellites is much longer, lasting from 22.5 min to 107 min. The unhealthy periods in the broadcast ephemeris are much longer than the actual maneuver periods when the thrust is applied.