Autonomous Navigation Using X-Ray Pulsars and Multirate Processing

In this paper, autonomous pulsar-based spacecraft navigation is formulated in terms of a single nonlinear filter. The observability and the positioning accuracy of a spacecraft traveling at known constant velocity are analyzed to build insights into the general navigation problem. A variation of the extended Kalman filter is developed and implemented to track Poisson pulsar measurements collected by an orbiting spacecraft. This filter leverages multirate structure to more efficiently process pulsar measurements. An alternative formulation using quadrature is studied, and its performance is compared to the typical phase approach. Simulation results for an orbiter mission and a deep-space mission are presented to show the accuracy of pulsar-based navigation in space.