Deep Space Navigation Using Celestial X-ray Sources

Paul S. Ray, Suneel I. Sheikh, Paul H. Graven, Michael T. Wolff, Kent S. Wood, Keith C. Gendreau

Abstract:	Spacecraft traveling into deep space operate well beyond the useful range of the Global Positioning System (GPS) and yet still may have requirements for precise navigation information for trajectory calculations, instrument operations, or communications. The current predominant source of navigation information for deep space probes is range and range rate information obtained as part of the uplink and downlink communication with ground stations such as NASA’s Deep Space Network (DSN). These systems are expensive to build and maintain and time on them is a scarce resource because of their support of many concurrent missions. In addition, the navigation information obtained naturally achieves much higher precision in the radial dimension than in the two transverse directions. Consequently, a source of navigation information that does not rely on frequent communications with Earth-based assets and that attains high accuracy in all directions would be highly desirable. In this paper, we describe one such source of navigation information: celestial X-ray sources. Several classes of Xray sources, particularly X-ray pulsars, produce regular time signatures that can be predicted with very high accuracy over long timescales. By observing the arrival time of pulses at a spacecraft from several pulsars in different directions, a spacecraft could autonomously determine its location with respect to an inertial origin in a manner similar to GPS. This technique is applicable anywhere in the Solar System, and beyond. The relatively low disturbance environment of deep space, as compared with low-Earth orbit, allows pulse times-of-arrival (TOAs) to be measured using long integrations in order to make useful position determinations. Source characteristics and X-ray detector techniques are described herein, along with methods to use this source signal to supplement ground tracking observations to enable greater autonomy, increased navigation performance, and reduced resource requirements for future deep space missions.
Published in:	Proceedings of the 2008 National Technical Meeting of The Institute of Navigation January 28 - 30, 2008 The Catamaran Resort Hotel San Diego, CA
Pages:	101 - 109
Cite this article:	Ray, Paul S., Sheikh, Suneel I., Graven, Paul H., Wolff, Michael T., Wood, Kent S., Gendreau, Keith C., "Deep Space Navigation Using Celestial X-ray Sources," Proceedings of the 2008 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2008, pp. 101-109.
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