XNAV for Deep Space Navigation


The concept of utilizing pulsars for spacecraft navigation has been in development since the discovery of these rapidly rotating neutron stars in the 1960’s [1]. The Jet Propulsion Laboratory (JPL) conducted studies in the 70’s and 80’s proposing the use of the pulsar signals as navigation beacons in both the radio and X-ray bands of the electromagnetic spectrum [2, 3]. Since the 80’s, the Naval Research Laboratory (NRL) has researched X-ray sources and developed detectors providing the foundations for X-ray source spacecraft navigation development. Several important dissertation researches were pursued within the 90’s and 00’s [4-7]. During the last several years the Defense Advanced Research Projects Agency (DARPA) and NASA have supported more in depth development focused on the preparation of an operating instrument for an eventual space flight demonstration. Preliminary results suggest that XNAV becomes competitive with current radiometric methods, in terms of navigation performance, at ~109 km – near the range to Jupiter when Jupiter and Earth are in opposition. As range from Earth grows from there, XNAV becomes an increasingly attractive alternative, and may be mission enabling for very deep space applications such as investigation of the Pioneer Anomaly [8], as well as unique orbit applications such as the Earth-Sun Libration
(L2) point.
This paper provides an overview of the basic principles of X-ray pulsar source based navigation and timing (XNAV), followed by a discussion of elements of a navigation error budget focused specifically on deep space applications. Several potential NASA applications are identified, including Earth-Sun L2, outer planetary, and very deep space missions. Finally, some preliminary comparisons with Deep Space Network (DSN) based radiometric methods are presented.

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Graven, P., J. Collins, S. Sheikh, L.J. Hansen, P. Ray and K. Wood. 31st Annual AAS Guidance and Control Conference. Breckenridge, CO. February 1–6, 2008.