Storm drive

A storm drive was a powerful engine which used nuclear fission to produce energy to power a starship. The destruction of a storm drive would cause a major energy release, equivalent to an atomic bomb, and would leave massive amounts of residual radiation.

There was a storm drive powering the Titanic and, without it functioning, the ship would lose orbit. In an alternate timeline the engines failed and the Titanic fell on London, destroying it and poisoning all of Southern Wales. In the original timeline, the Doctor managed to use the heat of reentry into Earth's atmosphere to fire up a secondary storm drive and return the Titanic to orbit. The secondary storm drive was enough to keep the ship in orbit until rescue could arrive. (TV: Voyage of the Damned)