Doppler/XNAV-integrated navigation system using small-area X-ray sensor

To reduce the area of an X-ray sensor, a Doppler/XNAV (X-ray pulsar-based navigation)-integrated navigation system is proposed. The Doppler navigation, which utilises the radial velocity relative to the Sun as the measurement information, can provide highly accurate velocity information. However, this method is completely unobservable, and cannot be used to navigate alone. The XNAV system utilising three or more pulsars is completely observable, but its navigation accuracy is low when the area of the X-ray sensor is small. As two methods are complementary to each other, a federated filter is utilised here to fuse the information from the XNAV and the Doppler navigation subsystems. As both the state and the measurement equations of two methods are non-linear, the UKF (Unscented Kalman Filter) is used as the local filters of the federated filter. Compared with XNAV, this integrated navigation method can provide better navigation performance. The simulation results demonstrate the feasibility and accuracy of this navigation method with a small-area X-ray sensor.