ION GNSS 2012
Session A2: Algorithms & Methods 2: Navigation & Supplementing GNSS

Title: Autonomous Navigation for Navigation Satellite Constellations Using X-ray Pulsars
Author(s): F. Wu, X. Sui, Y. Zhao, Beihang University, China
Date/Time: Wednesday, September 19, 2012, 5:08 p.m.
Room: 204 (NCC)

Global Navigation Satellite System (GNSS), such as GPS, GLONASS, GELILEO, and BEIDOU have nowadays contributed a lot to civil, marine, air and land navigate applications. Presently, these navigation systems, all composed by several satellites in a constellation respectively, can provide accurate, continuous, three-dimensional position and velocity information to users with the appropriate receiving equipments.
One of the issues that have received much attention is that GPS satellites need continuous information from master monitor stations on the Earth, which makes the navigation of themselves non-autonomous. As there being great deal of numbers of satellites in a constellation, it brings burdensome operations for system administers using traditional earth-based mode of orbits keeping and determination. Furthermore, reliability of earth-based mode with few stations controlling multiple of satellites is not fully credible. So, it is highlighted that autonomous navigation is the one meets the need of navigation constellation development. An autonomous way to achieve constellation navigation is based on cross-links. However, a problem that the constellation rotating errors are accumulating with time is truly exiting. It is very difficult to keep the constellation autonomously operating for a long time. Using the X-ray pulsar based navigation system is a new approach to solve the constellation rotation issue, and meets the need of being independent from earth monitor stations.

This paper investigates a method of autonomous navigation for satellite navigation constellations based on X-ray pulsars. When the X-ray photons from the pulsars are detected with the onboard detector, pulsars´ pulse profiles are folded and the image can be obtained. From the detection, the time of arrival (TOA) of the pulsar´s signal is recorded with the onboard atomic clocks. Moreover, the navigation parameters for the satellites, including the position, velocity and time, can be resolved accurately by the data processing of TOAs. All of the processes can be implemented by onboard computers. During the procedure of deriving the orbit information, errors are caused by observation of the pulsars´ angle position error, solar barycenter position error and the transformation of TOAs error. This paper provides an analysis of errors´ effects on navigation accuracy, means of mitigating the errors are proposed as well. In order to assess the feasibility and accuracy of the approach and the algorithm, a simulation for navigation of GPS constellation utilizing X-ray pulsars is carried out, which finally shows that it is a potential and effected way to realize autonomous navigation for satellite navigation constellations.

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