I have found a chest on the moon that I am unable to open. If you spawn in free roam, head up the hill and to the left, it's the first building you come to. Inside there is a bunch of computers around the room, helium spawns on the floor as well as the occasional chest. Sometimes, a chest spawns in the back right of the room, up on top of one of the machines. When it does this, it is un-openable.