GPS in space

The global positioning system (GPS) run by the US Department of Defense makes it very easy to find your position anywhere on Earth, but what if you’re not on Earth? What if you’re in space? At the moment researchers rely on simple time of flight calculations using antennae spaced out across the Earth’s surface to work out where their probes are, but this method becomes increasingly inaccurate as the distance to objects increases. (As an example, the error in the position of an object at the orbit of the most distant planet, Neptune, is about 120 kilometres.)

A group led by Professor Werner Becker from the Max Planck Institute for Extraterrestrial Physics in Germany think they might have a way to make a “GPS for Space” using X-ray pulsars.


A pulsar (“pulsating star”) is formed when a massive star explodes in a supernova, compressing the star’s core into a highly magnetised fast-rotating neutron star that emits a beam of electromagnetic radiation. The period of rotation of a pulsar is very short (milliseconds to seconds), and the the invariance of the period of rotation of some pulsars rivals atomic clocks in their accuracy.


Because each pulsar has a characteristic period of rotation it is easy to identify a signal as having been received from one specific pulsar. By mapping the position of hundreds or thousands of highly accurate pulsars relative to each other, and comparing the signals received at a spacecraft’s location with the data for a reference location it should be possible to map an object’s position anywhere within our galaxy to an accuracy of five kilometres, an incredible degree of accuracy. This is a little bit like being able to measure your position on the surface of Earth to within the width of an atom or two!

More information:

  • Becker et al, “Timing X-ray Pulsars with Application to Spacecraft Navigation”, arXiv:1011.5095.
  • Becker et al, “Autonomous Spacecraft Navigation Based on Pulsar Timing Information”,  arXiv:1111.1138.

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