Charged Vacuum Emboitement
A Charged Vacuum Emboitment or CVE] served as a transit point between N-Space and E-Space. The Logopolitans created the CVE's using block transfer calculations as a mean to siphon entropy out of N-Space and into E-Space and in this way forestall the death of the universe. CVE's operated passively, drawing physical objects through it as well as entropy. Because of their special function, the closure of the CVE's, then, threatending the physical integrity of N-Space and all life there. (DW: Logopolis, NA: Timewyrm: Apocalypse).
While in flight, the Doctor's TARDIS travelled through a CVE into E-Space by accident (DW: Full Circle). A similar event may have happened to the Human ship Hydrax (DW: State of Decay).