Imagine an unknown journey without now commonplace GPS systems. Ping a quick signal between a few pieces of high flying space hardware and you know exactly where you are. Now two astronomers believe they have an equivalent system, a sort of cosmic TomTom than can pin your galactic position down to the nearest metre.
Yet in deep-space dialling up a satellite in Earth orbit would be pretty useless, so instead the new system proposed by astronomers Bartolome Coll and Albert Tarantola uses pulsars. Pulsars are the rapidly rotating, super-dense relics of massive stars that give out very precise and regular signals of radio waves. By measuring the arrival times of these stellar pulses from four different pulsars you can work out where you are in relation to them.
On the vast scales that any future wider exploration beyond our Solar System would require, Einstein’s relativity comes into play and that is why four pulsars beacons are needed to map out space-time; three to cover the dimensions of space and the other to deal with time.
The only limitation to precision of the arriving signal is interaction with the interstellar medium but this only affects the pulses on the order of nanoseconds (billionths of a second) which translates into an accuracy of the nearest metre.