GPS may also work on the Moon

Scientists from NASA's Jet Propulsion Lab cited by IEEE Spectrum calculated that it's possible to use the GPS satellite system on the Moon. While GPS is designed for navigation on Earth, the scientists found that the existing infrastructure can also be used to guide astronauts in lunar orbit, 385,000 km away.

Cheung and Lee plotted the orbits of navigation satellites from the United States’s Global Positioning System and two of its counterparts, Europe’s Galileo and Russia’s GLONASS system—81 satellites in all. Most of them have directional antennas transmitting toward Earth’s surface, but their signals also radiate into space. Those signals, say the researchers, are strong enough to be read by spacecraft with fairly compact receivers near the moon. Cheung, Lee and their team calculated that a spacecraft in lunar orbit would be able to “see” between five and 13 satellites’ signals at any given time—enough to accurately determine its position in space to within 200 to 300 meters. In computer simulations, they were able to implement various methods for improving the accuracy substantially from there.

Navigating on the Moon itself will be more of a challenge, but could be resolved via two satellites in lunar orbit. The existing Lunar Reconnaissance Orbiter could be used for this, which means only a new relay satellite in high lunar orbit to act as a locator beacon is needed to help future lunar astronauts to navigate on the surface of the Moon.