Ill answer for them. They are using a startracker, meaning the camera rotates at the same rotation of the earth meaning they won't ever get star streaks.

Without a startracker, the wider your lens, the longer you can take a photo for. You can divide 500 by your focal length (lets say 20) and you'll get how long you can shoot in seconds for that focal length, so 500/20 = 25seconds is the longest before you get streaks using a 20mm lens. In practice this is a bit too much in my experience but, it's close enough for napkin math.