The Dimensional Fold Drive is an extension of existing Warp Drive technology. It was developed by melding Hyperspace technology produced and sold by Excalibur Inc. and Federation Warp Drive technology. It is used to travel not only through space, but also through time.
Operation
The drive works by manipulating an existing warp field produced by a standard warp drive system with temporal energy. This energy is modulated to match the shape and output of the warp field. This solves the instability problem at warp power surpasses Warp 9. Instead of the warp curve becoming asymptotic above Warp 9 as power approaches Warp 10 (infinite velocity) the curve becomes manageable in both velocity, power output, and power consumption.
In normal space flight at high warp the temporal energy output is kept equal to the power output of the subspace field created by the warp drive. When the temporal energy is increased, at around twice the warp power output the temporal energy added to the warp field folds space-time around the ship by modulating the temporal energy and shaping the saturated warp field the ship can travel through space and time simultaneously. This is called "Folded Space", around this bubble of space-time is a void between dimensional layers called "Null Space".
Neither matter nor energy can exist for more than seconds before being pushed back into normal space at random. A ship or person cannot survive intact the uncontrolled transition intact. A ship's debris would be spread over an entire sector or farther, if folded space collapsed around it.
Velocity
Velocities are measured in chochranes like with Warp Drive as multiples of c (light speed) adjusted for variations caused by local space composition, gravity, and subspace geometry. While normal Warp Drive has a speed curve of roughly warp factor raised to the 3 and 1/3 power, Folding allows for a steeper speed curve of folding factor raised to the 3 and 2/3 power.
It may be possible to push the envelope further into the dimensional void to achieve greater speed, but it is likely not safe with current technological limitations.
Time Travel
When in Folded Space a vessel can alter its delta-T vector (direction and velocity of travel through time) but also may keep the delta-T set to 0, where the vessel will not travel through time except along its normal, natural, speed and direction. Altering the delta-T also uses considerably more power than simply traveling in the three spacial dimensions.
Terminology
Terminology used to differentiate between speed requests or in reporting speeds for course corrections or other records is warp 9 is Warp Drive. A similar speed with folded drive is termed as Fold 9, meaning traveling in folded space.