Reactor
The reactor is the heart of any ship in the Freespace universe, providing power to all its systems. Terran and Vasudan reactors are fusion based, and run off deuterium collected by Anukhet and Zephyrus gas miners.
Vasudan reactors are known to be particularly efficient, and provide the power for the GTCv Deimos class of corvettes, which, tonne for tonne, produce more energy than any other vessel in the allied fleet.
Data on Shivan reactor systems is limited, but they are apparently quite volatile, as it was the destruction of the SD Lucifers five reactors which led to the destruction of the ship itself. Destroying the reactors on other classes of Shivan vessel does not destroy them, so this may have been a peculiarity of the Lucifer class, or a sresult of their being destroyed while the vessel was in subspace.