Titan base was a large filling station on Titan in the early 51st century. It had a crew of four. Three of them worked in shifts, arriving on the base by Titan shuttle and staying until a relief crew arrived. The fourth crew member was the commander, who seemed to have been a permanent inhabitant of the base.
In the year 5000, a relief crew infected by the Swarm took over Titan Base and tried to turn it into a Hive. The Fourth Doctor ignited fuel tanks at the base, which coupled with methane in the atmosphere to create an explosion which destroyed the base. (TV: The Invisible Enemy)