The Reactor is the main system on the power bus that creates power. In the Engineering Software there are two reactors, the Habitat reactor, and the Ayse reactor. Both of these reactors work on the same principles, but the Ayse reactor is capable of much higher power output.
The Habitat uses a tokamak reactor which uses a deuterium-tritium fusion reaction to generate power. The reactor is supplied with fuel from the main fuel tanks, which contain 78 t of lithium and 22 t of deuterium. When refueling, if there is no access to deuterium and tritium, hydrogen can be used instead although the reaction will not be as efficient, and will produce less power.
The Ayse Drive uses the same tokamak style fusion reactor as the Habitat, except on a much larger scale; the reactor is 14.5x more powerful then the Habitat reactor. Fuel is provided by an enormous 15,000,000 t fuel tank, which contains 11,700,000 t of lithiun and 4,300,000 t of deuterium.