Matryoshka drive

A Matryoshka drive was a type of engine that theoretically used a lifeless, collapsing universe caught in a multi-dimensional sphere as a source of limitless energy. However, according to the Ninth Doctor, the technology was extremely dangerous and would eventually by banned by every civilized race in the cosmos after it was discovered that the universes inside were not as lifeless as believed. Each, in fact, contained "trillions of worlds, all screaming in agony".

In the 53rd century, the Hesguard Institute would use a Matryoshka drive to power the station, including the fields that prevented it from being destroyed by the Time Storm surrounding the facility. The Doctor would describe their technology as "Fantastic", while acknowledging that it also violated at least nine edicts of the Shadow Proclamation. (COMIC: Sin-Eaters)