Extended Kalman filter for optimal determination of position, velocity and time of Earth orbiting satellites using carrier phase measurements from GNSS constellations

Global Navigation Satellite System (GNSS) sensors on-board the space crafts are providing orbit determination solutions very efficiently. Evolutionary improvements in spatial, spectral and temporal resolution of instruments require increased precision in orbit determination, satellite attitude and control. This can be achieved having highly precise position data available by the use of carrier-code combinations with a multi-channel dual-frequency GNSS receiver. The research focuses on the enhanced accuracy and performance improvement of the navigation solution for real time orbit determination. Dual frequency Ionosphere-free combination of integrated carrier phase is used as a measurement in an extended Kalman filter. By using carrier-phase data range biases are introduced for each channel of the receiver and are required to be resolved as part of estimation process. In addition to user-spacecraft position and velocity, receiver clock offset, drag coefficient and solar radiation pressure coefficient are added to the Kalman state vector for improved accuracy. Empirical accelerations in the state vector denote the inaccuracies of the adapted dynamic models of the spacecraft motion and are very effective for a nominal performance of the navigation solution in case of a manoeuvre. The system dynamics comprise of forces acting on a spacecraft in LEO. The states are propagated for the time update of a Kalman filter with a Runge-Kutta 4th order integration method. The measurement update is carried out sequentially for simplicity of the computation. Software testing is carried out via a Simulink based GNSS simulator environment to verify the results to the targeted accuracy. Filter parameters are tuned for performance improvements