The Levels of Space
To better understand how FTL travel works, you first have to understand the Levels of Space and how they function. Space as a whole exists in layers, some longer than others, some shorter. If you want to think of it in physical terms, imagine you're in a submarine in the ocean, and your ship is sitting on the surface. That is the state where you're in "normal space" as you've achieved the spacial equivalent of "neutral buoyancy." To reach "subspace" you would need to reduce your buoyancy so that your submarine sank to a lower level. Traveling into subspace works the same way. FTL transit fields created by the nacelles and FTL engines of systems such as Warp Drive, Coaxial Drive, hyperdrive and such create a state of negative buoyancy within space itself, allowing you to descend into lower levels of space where the distances between objects is considerably shorter.
In the same way, super space (the space above normal space) can be reached by increasing your proverbial spacial buoyancy, allowing you to rise up into those layers. The only reason super space hasn't been explored is there's no benefit to go there, as travel is considerably slow, and distances are greater, plus energy levels are much reduced, creating somewhat the same effect as the gradually reducing pressures of ascending upward in either the atmosphere, or the water, where pressures become lesser the closer you get to the surface. The only drives known to disobey this principle are those that travel at superluminal speeds, or directly fold normal space, such as in the case of Jump Drive, or create wormholes between locations, such as Wormhole Drive. All other drive systems use some form of subspacial submersion to achieve FTL speeds.
The total number of levels within space as a whole is not known, nor is it known how deep, or how high the scope of space goes. Where we exist in the scale of spacial levels is also not known. However, it's assumed that we exist somewhere between the middle of the pyramid of levels, and the upper third, with the majority of levels below us vs above. Systems that employ dimensional jumping or time travel do not qualify as an FTL, or Faster Than Light system of travel as they completely circumvent normal space by going around it using either time, or travel in and out of the dimension, thus the speed at which the ship travels is not faster than light.
