Not sure if this is relavant as most of you are talking about more simple methods of gaining location...
But anyone here play Space Engineers? The game has an integrated GPS-like location system. I don't think the planets in Space Engineers rotate/orbit though, so I'm not sure how that would work in Astroneer's solar system. But the orbits are fixed, so they are predictable.
Maybe just plantary GPS setup by sending up small sattelites. The Terra planet has them by default, the other planets in the system requiring the player to set them up manually.
Its just an idea.