Pulsar-Based Navigation and Timing: Analysis and Estimation
Millisecond pulsars are extremely stable and rapidly rotating neutron stars that emit electromagnetic radiation along their magnetic axes. Due to the misalignment between the rotational and the magnetic axes, the observed pulsar signals are analogous to the light beams of distant lighthouses. The predictable pulsing behavior is the fundamental mechanism that allows researchers to use pulsars as tools for science and engineering. This research focused on the analysis, simulation, estimation, and verification associated with pulsar-based navigation and clock calibration.
The autonomous pulsar-based navigation problem is formulated in terms of a nonlinear filtering problem where a single filter is used to estimate the spacecraft position and velocity. The positioning accuracy of a spacecraft traveling at known constant velocity was analyzed to build insights into the general navigation problem. An analytical comparison between the measurement noises of X-ray based and radio based pulsar timing/navigation system is discussed. A variation of the Extended Kalman Filter was developed and implemented to track simulated X-ray pulsar measurements collected by an orbiting spacecraft. This filter uses a multirate structure to more efficiently process pulsar measurements. The ephemeris of the DAWN spacecraft was used to investigate the performance of pulsar-based navigation in a more realistic mission scenario.
In order to show the feasibility of pulsar-based navigation, several existing pulsar tim- ing software packages and publicly available radio millisecond pulsar data were used to experimentally verify the concept. An Unscented Kalman Filter was used to process the time-of-arrival measurements from 5 isolated millisecond pulsars in order to estimate the position of the radio telescope in Earth fixed coordinate system.
This research also investigated the theoretical frequency stability of pulsar-aided atomic clocks from power spectral densities. Hadamard variance was used to analyze the unfiltered and the filtered clock systems. The result of the analysis shows that pulsars have the potential of enhancing the long-term frequency stability of stand-alone compact atomic clocks.
The last chapter of this dissertation discusses relative positioning using differential phase measurement. The proposed method can be used to eliminate common mode errors embed- ded in the pulsar measurements when the two observed signal frequencies are known.