The Hyperspace-Subspace Barrier Coefficient is a subspace phenomena that was first discovered in early 2385 by the crew of the U.S.S. Explorer.
Function
The Hyperspace-Subspace Barrier Coefficient is a unique type of subspace reading which allowed for incredible warp speeds. Generally speaking, Warp travel is dependant on the subspace coefficient, or cochrane ratio, of the area. While most of the universe has a Cochrane Ratio of around 1, certain stellar phenomena can effect and enhance the ratio. For instance, normally, a ship moving at Warp 2 will guage around ten times the speed of light, relatively speaking. If the Cochrane Ratio is over 1, that speed can be enhanced without actually changing the warp speed of the vessel.
What the crew of the Explorer discovered, was that if one follows on the exact coordinates and mapping and follows along the various hyperspace shipping runs in the SW-1138 Galaxy, the Cochrane Ratio seems to be extraordinarily high, enabling trips across the galaxy that would normally take decades, to take weeks, or even days.
However, these subspace cooridoors are very fickle, and are generally rarely used. The path must be followed exactly- -in terms of exact spacial coordinates, the 'width' of each cooridoor seems to be only a few thousand kilometers wide. When combining these paths with a Quantum Slipstream Drive, these paths seem to be somewhat more fluid.
Use History
Starfleet first discovered this aspect when experimenting with the Quantum Slipstream Drive. It is expected that as more starships are equipped with Slipstream Drives, more ships will be able to take advantage of this phenomenon, enabling Starfleet to enjoy speeds similiar to that of hyperdrive-equipped vessels.
Important Notes
Yeah…this pretty much just an in-universe explanation as to how the hell a Starfleet ship can get to Coruscant without it taking 40 years.
