Sky Shutter is a satellite, launched by the player's species, in orbit around Timber Hearth. It was launched by Outer Wilds Ventures and is the first satellite ever launched. It looks like a larger version of the player's probe. You can see realtime pictures from the satellite in the Observatory. Every second, the satellite emits a blue light.
It is possible to knock Sky Shutter down from orbit by repeatedly pushing it with your ship. If it hits the wall of one of Timber Hearth's craters, it will stop and fall to the ground. If you return to the Observatory and see pictures from the satellite while it is crashed, you should be able to see through Timber Hearth.