GPS acts as a set of manmade stars whose signals we use for electronic navigation by boats and by aircraft here on Earth. But what happens in the future when space vessels explore the far reaches of the solar system and then leave the solar system altogether? (okay, this is a long time in the future we're talking here). Even if we develop the propulsion systems to make such voyages possible, these craft will still need to navigate and GPS obviously won't cut it.
One recent study suggests that future space voyagers will be able to use a type of neutron star called a pulsar that transmits very steady pulses of energy. Pulsars spread through the sky will be like GPS satellites. Space navigators can use the known location of the star and it precise pulses to determine position. That's the theory, anyway. Next to this sophisticated pulsar approach, using a GPS or even ding celestial navigation with a sextant sound downright simple!