Subspace
A more recent technology than hyperspace flight, subspace travel was pioneered nearly 350 years ago almost by accident. Many spacers had been aware for centuries that while traveling at higher gravitational bands that it was possible for a ship to encounter heavy interference and be destroyed or incapacitated due to the high levels of stress present at the highest velocities. This made travel on increasingly higher bands dangerous and was a hindrance to further improvements in the realm of faster than light travel.
Solarian researchers made a breakthrough discovery in the field of FTL-Physics in 462AE that quickly led to the development of the Dimensional Sublimation Drive, or DSD. Commonly referred to as a subspace drive, it works on the principle that once a ship attains a certain FTL velocity, a pocket of "real-space" is captured by the ship's expanded particle field and the craft "sublimates" into subspace, a dimension which is roughly analogous to real-space, with the exception that the points between objects are far more compacted. This allows a hyperspace distance which might otherwise take 6 months to be traversed to be crossed in 5 weeks. However, this great breakthrough comes at a price.
"Overexposure", an affliction known to spacers as being the result of too much time spent in subspace, has grown increasingly common among civilian and navy crew. Real-Space cohesion, or rather the integrity of the pocket of real-space trapped within a ship's particle field, begins to break down soon after entering subspace. Though a ship can usually spend upwards of 3 months submerged before it is forced to "resurface", the affects of subspace exposure grow worse with each passing day, with many spacers complaining of hallucinations, paranoia, and other symptoms becoming more and more common.
Conventional wisdom limits subspace sublimations to 2-week periods to avoid these affects, though naval vessels have been known to break this rule fairly often. Usually subspace travel is not necessary except when traversing vast distances or when time is vital. Though often used by merchants, it still is not considered safe enough for extensive civilian use.