Anti-grav propellant unit
From Tardis Wiki, the free Doctor Who reference
Anti-grav propellant units were the power source of Dalek flying saucers.
Their workings were secret, known only to Daleks with the rank of Commander or above, and unknown to humanity altogether, although it was understood on Earth that the units somehow worked by locally cancelling the effects of gravity. (PROSE: Inside a Skaro Saucer)
