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