Starships use Void engines to travel both interplanetary and interstellar distances. The first Void engines developed, nuclear engines use an explosive thermonuclear reaction to generate power and thrust. Plutonium pellets are continously accelerated into one another inside the fisson chamber at relativistic speeds-allowing for critical-mass reactions with smaller minimum sub-critical masses-the resulting fission explosion then detonating tritium inside the bomb chamber-lined with x-ray containment mirrors-creating a powerful thermonuclear explosion, energizing thermopiles in the bomb chamber and the exhaust chamber, the blast plasma being directed out of the exhaust chamber to drive the ship through space.