With advanced forcefields, it was discovered that gravity itself could be manipulated and used as a propulsion unit. However, this remained mostly in the realm of theoretical physics, as using artificial gravity generators as a propulsion system was incredibly inefficient. The Captured Drakh Cruiese, however, opened up a new avenue for the development of this technology. Basically, the Gravitic reaction drive manipulates gravity by inducing a graviton field around the engine pod, or the entire ship, depending on the size of the vessel, and warps the gravity around the vessel.
This uses a combination of gravity nullification, which can allow the vessel to float effortlessly above a planet, Gravity repulsion, for propulsion, and gravitic enhancers to increase the overall power of the drive. The end result is a ship that can change direction instantaneously, as well as accelerate to full velocity instantaneously, and dramatically reducing the engines that are required, reducing the mass of the vessel, and thereby increasing the maneuverability of the vessel that much more. While one gravitic engine is usually sufficient to propel a vessel, larger ships will generally require as many as four. Also, standard Plasma/interphased sublights engines are still mounted on the space-frame, to allow for minimum maneuverability, if the gravitic drives are taken offline, as well as acceleration augmentation for fast getaways.
Since the upper speed limit of the reaction drive approaches that of light itself, it can be used as a brute-force FTL drive, as well as a quick escape method, ultimately increasing the speed of starburst dramatically, by as many as 2 Hetch factors, depending on the ship.