The Graviton Engine is the primary source of propulsion for spacecraft of the New Commonwealth, the Free Worlds Alliance, and other space-faring races. It is the primary propulsion system for pathfinder ships, explorers, defenders, Aves, Aquilae, Fast Attack Ships and most forms of spacecraft.
The Graviton Engine works on the principle of compressing space-time in front of the ship and expanding it behind the ship; creating systolic motion in four-dimensins that push the ship forward.
The maximum achievable speed in normal space is light speed. Use of Graviton Engines at speeds above .55c create the potential for opening Trans-Dimensional gateways between normal space and hyperspace. These hyperspace shortcuts make inter-stellar transport possible.
To move very large ships, Graviton Engines must themselves be very large. The Graviton Engine Cores on a Pathfinder ship are over 100 meters in diameters. They are powered by sustained interactions by Quantum particles; a quirk of subatomic structure that allows subatomic particle reactions to produce more energy then is consumed in making them.
A side-effect of Graviton Engine propulsion at low planetary altitude is the imprinting of patterns (typically circular) on fields of grain crops. (Book 04 - Winter)