The ARK Reactor, the three letters an abbrievation for AmRuKuo, was a major energy production facility in Oasis on Mars right up until its destruction in the Battle of Oasis in the Second Martian Revolution. It was run by the AmRuKuo Corporation's energy division and was a key holding of the Earth Defense Force, south of the Oasis Industrial in a particularly concentrated area of EDF deployment.
Not only did the ARK Reactor have its own attached ARK Power Barracks along with a comprehensive layered defensive line along the only road in, but it was across the road from the main EDF Oasis Barracks. Furthermore, the Badlands side of that road was bisected by a large EDF outpost which provided a first line of defence against propective Marauder raids.