These are used on fighters, as docking engines, and on civilian micro-craft such as ore harvesters. On micro-craft rocket engines are the large boost engines, and Ion engines are the small boost ones. Ion engines have incredibly long lifespans, and require little reaction mass. They use electrostatic energy to create large thrust. Many larger military ships possess backup Ion engines, but if they don't say they have backup Ion engines, then they do not. Ion engine. Ion engines typically have thrust vectoring dependent on their use.