Posts Tagged ‘xnav’

XNAV, Don’t Leave Earth Without It

2010/07/18 Leave a comment

imageWhilst tinkering with my space simulator project, I started to think:

What sort of electronic navigation system would you use in space?  Would you have some inertial-based system as in the KA-50 helicopter?  Would you triangulate your position by tracking known stars?  Or maybe a really long piece of string and a protractor?

I didn’t have the foggiest idea. So Googling around I found many references to designs that referred to something called X-ray Navigation or XNAV. [1] [2]


Basically XNAV uses one or more x-ray emitting pulsars depending on your navigation needs.  Pulsars are basically stars that have gone BOOM and reduced themselves to a tiny neutron star which just happens to be spinning. An x-ray beam is emitted (Figure 2-6 [1]) in-line with the magnetic poles. Astronomers have found that pulsars are quite abundant in the measurable universe and that the spin of the pulsar is unique.  This uniqueness of the pulsar spin and resulting “flash” or “pulse” as the beam sweeps past you allows you to determine the source pulsar by measuring pulse intervals.

By using 3 pulsars, you can accurately triangulate your 3D position in space in the same way your car GPS can – albeit the latter in 2D only.

Just one pulsar please

Microcosm writes that a single pulsar is all that is needed for a satellite orbiting the Earth to accurately correct its trajectory since the satellite is changing position significantly with respect to the Earth.  Travel between planets usually requires at least 2 pulsars because the travel vector may not be significant with respect to the pulsar to deduce positioning. [2]

Other uses for XNAV include the ability to correct the ship’s clock based on timings from pulsars.

Problems exist for XNAV before it can be implemented such as issues resulting from General and Special Relativity since the vehicle is moving.  Darn.

Thank goodness my simulator will have the Acme Widget XNAV Extension 5000 which gets around such annoyances.

[1] Sheikh, Suneel Ismail, “The Use Of Variable Celestial X-ray Sources For Spacecraft Navigation”,, Copyright  © Digital Repository at the University of Maryland

[2] P. H. Graven1, J. T. Collins1, S. I. Sheikh2, J. E. Hanson3, “Spacecraft Navigation Using X-Ray Pulsars”, Microcosm,

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