A novel non-conservative perturbation model for enhanced Precise Orbit Determination of BDS-3 SECM satellites

Next to the gravitation of the Earth and main celestial bodies, Solar Radiation Pressure (SRP) forms a dominate non-conservative perturbation acceleration acting on navigation satellites, which requires its careful consideration in Precise Orbit Determination (POD). When using the traditional empirical ECOM2 (Extended CODE Orbit Model) as SRP model in POD, the large systematic errors are observed for some satellites, and orbital accuracy level is different among satellites from different manufacturers. To address this issue, we developed an improved non-conservative perturbation model for BDS-3 satellites, focusing particularly on satellites manufactured by SECM (Shanghai Engineering Center for Microsatellites). Initially, a priori analytical Box-Wing (BW) model was introduced to POD, fully incorporating satellite metadata and orbital plane characteristics. This improvement significantly benefits two SECM satellites, namely C25 and C26, in orbital Plane-C, eliminating a large number of systematic errors with their radial orbital accuracy reducing from 9.79 cm to 1.41 cm. To further enhance SECM satellites in Plane-A, we analyzed the correlations among SRP parameters derived from the post-fitting variance–covariance matrix, as well as spectral analysis of SRP accelerations. We conclude that BW as a priori SRP model takes partially into consideration the second-order sine and cosine terms of ECOM2 in $D$ direction. Subsequently, a simplified novel model, BW+iECOM2, has been written by keeping four-order terms from ECOM2 and estimating them with a priori constraint. This adjustment resulted in positive impact on geodetic parameters and an additional 11.3% improvement in radial component accuracy for SECM satellites. Overall, this novel model allows to achieve orbital accuracies of (1.92, 2.29, 1.87) cm for CAST (China Academy of Space Technology), (2.74, 2.46, 1.82) cm for SECM, and (5.28, 2.80, 2.73) cm for IGSO (Inclined Geosynchronous Orbit) satellites in the radial, along-track, and cross-track components, respectively. Furthermore, validation of the novel model demonstrated significant enhancements. The orbit Signal-In-Space Range Error (SISRE) relative to GBM (Multi-GNSS precise products of GFZ) decreased by 51.0% compared to the ECOM2 strategy. The standard deviation (STD) of Satellite Laser Ranging (SLR) residuals indicated a 7.4% improvement in radial accuracy for SECM-A Plane-A satellites and a 46.5% improvement for SECM Plane-C satellites, when using the novel model. Additionally, static and kinematic Precise Point Positioning (PPP) showed improvements of 32.7% and 34.5%, respectively, particularly in the east component.