So we have our craft, and we are ready to explore the cosmos, now how do we find our way around. Aim at a star and go right? Probably not. Some of the stars visible in our night sky are extinct. Given the speed of light, and the fact that what we see on any given clear night may have taken billions of years to reach us, the source of that light may have died, or been devoured by a black hole millions of years ago. In theory we could approach the point where the light of the extinct star we were using for a beacon, simply vanishes. It could be like trying to reach a distant shore and having the lighthouse we were using as our guide suddenly going out.
In taking the lighthouse metaphor a bit further, researchers aboard the International Space Station designed a navigation experiment using the rotating radiation bursts from pulsars that sweep past Earth with a predictable regularity. Using an instrument known as the Station Explorer for X-ray Timing and Navigation Technology experiment, or SEXTANT, the I.S.S. was able to determine its own position to within 10 kilometers. SEXTANT, used an array of 52 X-ray telescopes to gather and measure the signals from 5 pulsars. The experiment works a bit like GPS on Earth that uses the timing of signals from satellites to determine the position of a phone, or GPS receiver. Ten kilometers doesn’t seem like that much of an accomplishment when compared to the accuracy of earthly GPS, however the further one travels from Earth the less reliable the current navigation technique using terrestrial radio telescopes becomes. If a ship were navigating to a far flung planet, like Neptune or Pluto, the pulsar navigation could provide much better position estimates than earthbound radio telescopes could provide.
This is not the first time that someone has thought of using pulsars as a navigational aid. Carl Sagan was tasked with producing a message to be affixed to the Voyager spacecraft before they were launched on their epic odysseys. On the gold record of each there is a map using fifteen radiating lines that mark the directions to fifteen pulsars. Each of these is in turn flanked by the frequency of the pulsar given in binary code in multiples of 1.420405 GHz (a common vibratory frequency of hydrogen) Pulsars have unique signatures that remain stable, so it was hoped that any civilization that recovered the golden album from a Voyager probe would be able to use the pulsar map to determine the location of Earth.