Space Station Z-7

Space Station Z-7 was a space station which was captured by rebel forces who used space mines to fortify it against intruders. When the Doctor's TARDIS materialised on board, the Doctor, John and Gillian were captured and brought to the rebel leader, who demanded to know how they got past the mines, and wanted the Doctor's help in perfecting his doomsday machine, which he planned to use to conquer the universe. John and Gillian escaped, freed the Doctor, and together they used the station's radio to summon a rescue ship, deactivated the mines to allow the ship through, then reactivated them again when the rebels escaped, killing them and destroying their doomsday machine. (TVC: Space Station Z-7)