The Gravitonic Accelerator is a special ability granted to three Privateer ship designs. Even though the Privateers builds these, anybody that controls the Br4 Class Gunship, the Br5 Kaye Class Torpedo Boat, and the Meteor Class Blockade Runner benefits from these ships.
This ability allows the ships to move at twice the normal speed per turn, while burning half as normal neutronium per light year. This makes these ships extremely potent for any non-direct combat purpose.
They also count as having double the warp factor for purposes of establishing (but not breaking) a tow lock. A gravitonic ship set to warp 5 (or greater) will lock down any vessel that does not successfully get towed away by a lower ID ship.