Part magic gravity, part inverted centrifugal force. 
Whoever decided this is either incredibly dumb, or they meant to insult the viewer. Part of the ship rotates to simulate gravity, seems plausible at first until you notice that the gravity pulls towards the centre of the rings. And later they show there is gravity everywhere on the ship, not only in the centrifugal rings.

I generally find this show entertaining, but this episode is a total waste of time.