Sentinel-6A GPS and Galileo Dual-Frequency Real-Time Reduced-Dynamics P2OD

Onboard navigation is an essential task to ensure satellite autonomy. Especially for real-time operations, high-accuracy satellite positioning is required. In this context, the Sentinel-6A (S6A) dual-constellation GPS and Galileo measurements are exploited to assess the Precise Onboard Orbit Determination (P2OD) performance achievable using an Extended Kalman Filter (EKF) algorithm with a reduced-dynamics approach. Commonly, high-accuracy GNSS orbits and clocks are needed to obtain a high-quality Precise Orbit Determination (POD) solution. However, such products are not available onboard, where only broadcast navigation data can be retrieved. Here, the results employing different qualities of GNSS orbits and clocks are presented, considering five consecutive days of S6A GNSS measurements. Furthermore, the impact of using broadcast ephemerides is investigated along with adopting either a single- or dual-constellation configuration. Results indicate that the use of Galileo dual-frequency measurements and broadcast ephemerides leads to decimeter-level orbital accuracy, showing, in a dual-constellation configuration, a 11 cm 3D RMS position difference w.r.t. precise reference orbits. This marks an improvement of a factor larger than two w.r.t. using GPS-only broadcast ephemerides, and enables a new level of accuracy for P2OD.