Research On Relative Measurement For Formation Flying Satellites

Satellite formation flying is currently one of the focuses study in the domain of spaceflight.Many key technologies of formation flying satellites depend on the relative navigation, which means the state and filter estimate of relative position and velocity. Therefore, enhancing the quality of the relative navigation accuracy influences the success of satellites formation missions. In the previous basis, this thesis makes further study of relative navigation for formation flying satellites.Firstly, several discription of relative dynamics for formation satellites is studied. This thesis defines the reference coordinate system, then deduces the model of relative dynamics for formation satellites. On the basis of accurate nonlinear dynamical model, this thesis derives the simplified linear equations, which includes Lawden equation and Hill equation. This thesis also gives the analytical solution and the periodic condition of the linear equation, and makes the simulation to contrast the accuracy of the linear equations. Based on the simulation results, a appropriate state equation model is provided for relative navigation.Secondly, the GPS navigation system is described and a semi-physical simulation experiment of GPS is carried. This thesis makes an overview of GPS system, which includes GPS pseudo-range measurement, carrier phase differential GPS, GPS satellites coordinates calculating based on GPS broadcast ephemeris, and the process of GPS relative navigation. The semi-physical simulation experiment is carried with OEMV hardware system. The simulation environment, OEMV hardware system and serial communication are all provided in detail. Thirdly, a Robust Kalman Filter is used in relative navigation for formation flying satellites. To improve the stability and computation precision of the relative navigation of formation flying satellites, a robust Kalman filter (RKF) was presented for estimate of relative position and velocity. Lawden equation is modified to be the state equation of RKF Filter system. Compared with the EKF filter results, the algorithm provides obvious advantages including higher navigation precision and stronger robustness. Simulation results indicate that the relative navigation using RKF is effective in practical applications.Finally, GPS/RADIO integrated navigation system using federated Kalman filtering is proposed for the ultra-close spacecraft formation flying. The structure and model of GPS/RADIO integrated navigation system are described. Then a federated Kalman filtering is designed for GPS/RADIO integrated navigation. Simulation results indicate that GPS/RADIO integrated navigation system provides obvious higher navigation accuracy, which is thirty percent higher than a single subsystem, and the system can also improve the system fault-tolerant rate, which is effective in practical applications.