Without this system it is not possible to determine a spaceship's location precisely enough to engine-firing just right to go into orbit around a distant moon.
With this technology, autonomous spacecraft could thread a needle to get into orbit around the moon of a distant planet instead of doing a flyby according to NASA scientist Zaven Arzoumanian. A galactic positioning system could also provide "a fallback, so that if a crewed mission loses contact with the Earth, they'd still have navigation systems on board that are autonomous."
When your phone tries to determine its position in space, it listens with its radio to the precise ticking of clock signals coming from a fleet of GPS (global positioning) satellites in Earth orbit. The phone's GPS then uses the differences between those ticks to figure out its distance from each satellite, and uses that information to triangulate its own location in space.
Your phone's GPS works fast, but Arzoumian said the galactic positioning system would work slower —taking the time needed to traverse long stretches of deep space. It would be a small, swivel-mounted X-ray telescope, which would look a lot like the big, bulky NICER stripped down to its barest minimum components.