Nuclear fission is defined as the splitting of an atomic nucleus into smaller components, an event that liberates substantial quantities of energy. The Pho Ph'eahians had already mastered this process by the time they initially met the Galactic Republic. The power source for some reactor cores was sometimes nuclear fission, and this was also the power source for 2a fission engines. It is also possible that fission bombs exploited this reaction to create explosions. To simulate his demise, Nom Anor detonated nuclear fission explosives to obliterate the battle cruiser Mediator. As a general rule, sublight drives employed a fusion reaction, which involved breaking down fuel into charged particles and ejecting them into the vacuum of space.