The phased array gravity drive, more commonly known as the impeller drive, was the preeminent sublight propulsion mechanism for spacefaring vessels of the Post Diaspora era.
It could also be used for propulsion in hyperspace, but was highly dangerous when making contact with a gravity wave. Transforming it into a Warshawski sail largely removed this danger.
Function
The impeller drive created a pair of stressed gravity bands above and below a ship, known as the impeller wedge. In order to generate the wedge, a pair of impeller rings, located at the fore and aft ends of the ship, were required. The impeller rings contained 16 beta nodes. Around 1900 PD, the best acceleration for the impeller drive starship was well under 600 gravities.
The drive "tamed" gravity waves to be used in normal space, but was highly dangerous in hyperspace, until the invention of the Warshawski sail, which helped detect other gravity waves and objects. (HH1)
Impeller rings
An impeller ring, also sometimes called an impeller band, was a ring structure made up of numerous beta nodes. The two rings at the bow and stern of a vessel came together to form the impeller wedge.
Military-grade starships actually generated two layers of bands. This had the added effect of preventing analysis of the inner band, which reduced the enemy's ability to track a ship through the distortion of the bands. (HH1)
Alpha nodes
Alpha nodes were the component of the drive's band that propelled a vessel to near light speeds. Their size varied based on the size and strength of the impeller wedge to be generated. Alpha nodes were the primary nodes of the impeller drive.[1](HH1)
Beta nodes
The beta node was a secondary component of the drive. (HH1)
The Royal Manticoran Navy developed the Beta2 node, a more powerful version of the standard beta node.
Impeller wedge
The wedge was a pair of extremely powerful gravity bands located above and below the generating ship. Both bands were inclined such that the forward end, or "throat", was far deeper than the aft end, the "kilt". The wedge was capable of accelerating a vessel to near-light speed.
Due to the immense twisting and warping of space that occurred in the band, no known weapons could penetrate an impeller wedge in either direction. The dorsal and ventral aspects were invulnerable to attack as long as the wedge was up. The flanks, forward, and aft aspects of the vessel were exposed.[2]
The mechanics of the impeller wedge prevent the forward and aft aspects to be protected in the same fashion, as it would prevent a ship from accelerating. As a result, tacticians would most prefer to attack "down the throat" of an opponent, with an "up the kilt" attack being slightly less desirable due to its narrower aspect. (HH1)
A wedge was much larger in length and width than the ship that generated it. On a ship of the wall, width of the wedge "was measured in hundreds of kilometers," requiring plenty of distance between ships in formation. (HH8)
History
In 1246 PD, a functional impeller drive was perfected on the planet Beowulf. (HH1)