When humanity sends spacecraft beyond our solar system, those starships will have to know exactly where they are at all times. A newly proposed cosmic GPS system can track a spacecraft's location to within five kilometers anywhere in the galaxy.
The secrets to this system are pulsars, a special type of neutron star that rotate at short, extremely regular intervals. That last bit is crucial - because we can count on pulsars to always rotate at the exact same speed, which makes them useful timekeepers across even the vast reaches of space. Indeed, some pulsars that rotate every few milliseconds are actually comparable to atomic clocks in terms of precision and dependability.
According to Professor Werner Becker of the Max Planck Institute of Extraterrestrial Physics, we can use pulsars to track probes anywhere in the Milky Way. The complete predictability of these stars' rotations can be used by a spacecraft to determine its position in space to within about five kilometers. This would be accomplished by comparing its observations of various pulsars' emissions beams with what would be predicted for that given location in space.
Considering we can only track our most distant probes like Voyager and Pioneer - none of which have come even close to leaving the solar system - to within a hundred kilometers, this system wold be a massive improvement. While this level of accuracy would be most useful for exploration beyond our solar system - whether takes the form of interstellar probes, generation ships, or some as yet impossible faster-than-light craft - but it could also be of great use closer to home.
Probes that go no further from Earth than Mars can still only be tracked to within ten kilometers, and even getting that close requires painstaking, error-prone measurements from Earth. The pulsar system would allow probes to locate themselves with far greater precision and no reliance on Earth as a reference point. For future Mars missions, particularly crewed missions, that level of exactitude could well be essential for safety and success.
The only slight hiccup in all this is that the current equipment needed to detect pulsars is about 100 times too heavy to actually be usable. Since pulsars are primarily visible in X-ray wavelengths, we will need to develop lightweight X-ray mirrors, and those are still likely about 15 to 20 years away. According to Professor Becker, once those materials are available, constructing the first interstellar GPS will be a breeze.