Interface stabiliser
From Tardis Wiki, the free Doctor Who reference
The interface stabiliser was a TARDIS component necessary for a safe flight, though it was not impossible to fly a TARDIS without one. It resembled a red crystalline ruby with a glowing light, protected against sheer external forces like shock, pressure, extreme heat or cold, and radiation. It worked to keep the interior of the TARDIS connected to the outer plasmic shell; without it, the TARDIS experienced hull phasing. (AUDIO: Mistfall, Equilibrium)
