Slipspace

Summary
Slipspace travel has been the UNSC's main way of traveling from planet to planet, and star system to star system. Before this technology was discovered by Shaw and Fujikawa, the engineers who built the first Slipspace engine, mankind was never able to leave his home star system of Sol. But now the UNSC traverses the galaxy in spacecraft to whole new worlds.

This new engine allowed ships to tunnel into "the Slipstream" (also called "Slipspace"). Slipspace is a domain with alternate physical laws, allowing faster-than-light travel without relativistic side-effects. Faster-than-light travel is not instantaneous; "short" jumps routinely take up to two months, and "long" jumps can last six months or more.

The SFTE generated a resonance field, which when coupled with the unusual physics of the Slipstream, allowed for dramatically shorter transit times between stars; however, scientists noted an odd "flexibility" to temporal flow while inside the Slipstream. Though no human scientist is sure why travel time between stars is not constant, many theorize that there are "eddies" or "currents" within the Slipstream—there is generally a five to ten percent variance in travel times between stars. This temporal inconsistency has given military tacticians and strategists fits—hampering many coordinated attacks.

The Covenant have a very finely tuned version of this technology, and it is far superior to the UNSC's. Instead of simply tearing a hole into slipspace, it cuts a very fine slit and slips into slipspace with precision. It exits the same way, and can have pinpoint accuracy.

In Halo: First Strike, while inside the Ascendant Justice, Cortana manages to figure out how to make a slipspace jump from within the atmosphere of Threshold. Later, a Covenant AI manages to leak the data out to the rest of the Covenant. In Halo 2, the Prophet of Regret uses this knowledge to jump while directly over New Mombasa, destroying the city during The First Battle of Earth.