TT capsule

The term TT capsule was used to refer to some kinds of space-time vessels.

Gallifrey's timeships, the TARDISes, were commonly referred to as "TT capsules" on the planet itself in technical contexts, (TV: The Deadly Assassin) although the term "TARDIS" was also used in such contexts. (TV: The Name of the Doctor, etc.)

After the destruction of Gallifrey in the War in Heaven, TT capsules were hired out to temporal tourists who wanted to visit Gallifrey's prior history. (PROSE: Gallifrey: A Rough Guide)