From FEInfobase

Quantum Slipstream Drive

The Quantum Slipstream Drive (QSD) generates a sustained subspace pulse designed to open and maintain a conduit through subspace strata. The Quantum Slipstream Drive allows star ships to travel long distances at speeds well above the warp 9 barrier. The conduit is large enough for 2 medium sized Starfleet vessels to travel through with a ship equipped with the Quantum Slipstream Drive.

The drive was named by Dr Thatcher as the best way of describing the effect on a ship travelling within a conduit. The quantum mass of a ship is reduced to near zero allowing the molecules of the ship to quickly and easily pass through space with little or no resistance.

While Federation technology has advanced far enough to allow the development of the DSQ there are still drawbacks with the technology. A Quantum Slipstream Drive requires massive power reserves to open a conduit, often a ship will have to charge capacitors to provide the first rush of power. Starfleet have also been unable to break the 10 hour barrier, since the lost of the first Excalibur prototype work has continued on find out what causes the pulse to fail after prolonged use.

Currently Starfleet has one ship equipped with the Quantum Slipstream Drive, the Excalibur Class USS Excalibur which is currently serving as part of the SRI.