From The LNR Book of Knowledge

The reactor is the powerplant of the ship; it provides energy to all of the other ship components (with the exception of armor, which requires no reactor energy). For a ship to function properly, its reactor must be supplying more power than the ship's components are using. Every starter ship comes outfitted with a Prototype Reactor, which generates 8000 units of energy for the ship to use; while there are ships outfitted to require less reactor energy, it is highly encouraged to have a significant margin of spare reactor power.

• The Freelancer droid command "Reactor Overload" will increase the amount of energy that a reactor generates, at the cost of stressing the reactor component. Being destroyed, ejecting, or landing the ship will return the reactor generation to normal levels, but only ejecting or repairing the ship (either at a space station or with Shipwright-made repair kits) will fix the system stress.