These shields help to protect a TARDIS during Vortex travel. Without them the TARDIS will be vulnerable to any passing danger in the vortex. Despite the fact that the Vortex Shields interfere with telepathic communications between people who are in the ship and people who are in Normal Space, switching them off while in the Vortex is not recommended. If the Vortex Shields are overloaded the sub-neutron circuits will start to fail. With great difficulty Vortex Shields can be extended to imprison another Time Travel Capsule operating in the Vortex, however the shields can only hold the other capsule for 2 minutes. The TARDIS Defense Mechanism also acts to hide the TARDIS from potentially dangerous life forms that exist in the Vortex. The Exo-Shell has a Temporal Field, which protects its interior from temporal attacks. Vortex Wraiths would be destroyed by the TARDIS's defenses if they attempted to invade the interior. (also see Defense Force-Field Prisms)