An Ultradrive is a device which allows objects to enter Ultraspace.
Like with Hyperdrives, a number of Ultradrive designs have been created. They all require around a hundred times more power than a Hyperdrive would, and exert their influence over the ship and any objects attached.
An Ultradrive allows access into both Hyperspace and Ultraspace. It requires the same amount of power to get to the borderline as a good hyperdrive, allowing semi-Hyperspace existence, and will then allow the ship into Hyperspace.
Then it will reach the Ultraspace threshold and the object can exist in both Hyperspace and Ultraspace. Once this threshold is passed, the ship will be in Ultraspace.
If the critical power level is not supplied, the ship will drop back into Hyperspace, and then if insufficient power to stay there is added, it will drop into real space.