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 [+]Loading...["The Deadly Assassin (TV story)"]) although the term "TARDIS" was also used in such contexts. (TV: The Name of the Doctor [+]Loading...["The Name of the Doctor (TV story)"], 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 [+]Loading...["Gallifrey: A Rough Guide (short story)"])