The Shaw-Fujikawa Translight Engine (SFTE, or slipspace drive) is a human spacecraft propulsion system capable of making transitions to and from slipstream space and by extension allowing faster-than-light interstellar travel. The Covenant analogue functions on similar principles, but is referred to exclusively as a slipspace drive.
The engine was developed by a group of engineers and theoretical physicists led by Tobias Fleming Shaw and Wallace Fujikawa and was completed in April 2291. From that point onward, the drive became one of the most important technological innovations of humanity. The drive is not without limitations, however, although these may be partially because of slipstream physics rather than engineering imperfections. Short slips may take several months, whilst longer slips may take over half a year.
The Shaw-Fujikawa Translight Engine functions by creating ruptures, referred to in some sources as wormholes, between normal space and an alternate plane known as slipspace (also known as slipstream space and Shaw-Fujikawa space). The nonstandard physics of slipspace allow it to be used as a shortcut realm, facilitating interstellar travel between distant regions in reasonable time.
The engine makes ruptures by using high-power cyclic particle accelerators to generate microscopic black holes. Because of their low mass, Hawking radiation gives them a lifetime of around a nanosecond (or potentially a little longer than a whole second) before they evaporate into useless thermal energy. In that nanosecond, the engine manipulates them into forming a coherent rupture between normal space and the slipstream.
It should be noted that in real-world physics, black holes have been identified as a possible vector for constructing traversable wormholes, specifically by replacing the singularity with a path to a white hole in another universe.
It is unknown whether a slipspace drive has a role in accelerating a spacecraft through slipstream space, or whether conventional reaction thrusters are used. It is known that an engine remains active for the entire period that a spacecraft is in the slipstream, although its purpose during this period is unknown. When active, a Shaw-Fujikawa engine emits alpha (helium nuclei) and beta (fast electrons) particles.
Human slipspace drives were considered black boxes which were very difficult to repair or maintain after they went hot for the first time. Spartan-051 considered slipspace drives dangerous, noting the aforementioned radiation and that spacetime was said to distort around an active device. Dr. Halsey also observed that in the past, several technicians had simply vanished whilst manually adjusting a drive. Given their advanced technology, it is unknown whether the Covenant had a similar view.
There have been several occasions where a Shaw-Fujikawa Translight Engine has been used for purposes other than those intended.
Being more scientifically and technologically advanced than humanity (having stolen most of it notwithstanding), the Covenant have numerous advantages in slipspace propulsion systems. Whilst the Shaw-Fujikawa engine is said to “punch” a hole between realms using brute force, Covenant engines instead take a small rupture and delicately enlarge it with surgical precision. This allows the latter to execute far more accurate slips.
Covenant drives are generally more flexible than those of humans. They have twice been seen to execute in-atmosphere slipspace transitions (although the first time the drive in question was controlled by a human A.I.). Although two human ships utilizing the Shaw-Fujikawa engine are suspected of having successfully executed an in-atmosphere slipspace transition, this has not been irrefutably confirmed. In addition, Covenant drives can execute successful slips even if underpowered.
Another massive advantage of Covenant drives is that they travel significantly faster in slipspace than their human counterparts. Although exact velocities are difficult to measure accurately, human drives typically cover between 2-3 light-years per day, while Covenant ships have been known to travel more than 900 light-years in the same time. Forerunner Dreadnoughts have been calculated at over 2000 light-years per day.
The term for making a transition between normal space and the slipstream is “jump”. The term “slip” is also used. Halo Wars introduces additional terminology for the slipspace drive. It is referred to as an FTL (for "Faster Than Light") drive and FTL reactor several times, and the process of initializing it for a slip was referred to as “spinning up”. This may be an attempt to introduce more accessible nomenclature for newcomers to the Halo franchise. This also could be a reference to Battlestar Galactica as they also refer to preparation for use of an FTL drive as "spinning up". Another explanation is that the drive most likely requires time to power up the particle accelerators and reach the mini-black-hole-creating threshold. The accelerators are most likely circular, and the subatomic particles could be said to "spin" around the center of the accelerator.