[ He nods. ] Push until it moves. The senor'll trigger.

[ Because sci fi reasons. Look, I dunno, man. Anyway, ]

Because of gravity - and the lack of it. Something this size can't just plummet to the planet. The planet's gravity and the lack of gravity up here in space keeps the station in orbit - traveling around the planet - which is why it seems to be a moon, to the natives. It rises and sets. [ This explanation includes hand gestures, moving one hand around the other to illustrate the push and pull of the forces that keep Thesa where it is. ] If the station is out of power to keep it in that exact position and it ends up caught in the planet's gravity, what'll happen is a slow spiral. A decaying orbit. It'll take days, even weeks. And eventually it will fall, after it breaks atmosphere. I've been eyeballing measurements every so often, so I should be able to tell in a couple hours if that's happening, but I don't think there's any reason to think so, right now.