Red Planet Wayfinder: A GPS System for Mars

Future explorers of Mars will always need a way to know where they are, regardless of whether they’re rover automatons or flesh and blood humans.
To do that, NASA researchers and scientists alike have been studying the requirements for a potential global positioning satellite (GPS) system around Mars that could also function as a communications network. Their vision is a small flotilla of Mars spacecraft conducting their own science while watching over future robotic or human expeditions, then relaying data back to Earth.