FTL travel

FTL, short for faster-than-light, was a method of travelling faster than the speed of light that did not rely on the mass relay network. Once a vessel had made a jump through a relay, conventional FTL let it move around the surrounding space at reasonable speed. The drive that made this possible exposed element zero to electric currents to generate mass effect fields, lowering a ship's mass to the point where it could exceed lightspeed without the time dilation that would otherwise result. Together with the relays, FTL drive underpinned all interstellar travel in Citadel space.

How FTL drive worked#

An FTL drive was the device that let a ship travel faster than light through ordinary space. Its core worked by exposing element zero to electric currents, creating mass effect fields that reduced the mass of the vessel to the point where velocities beyond the speed of light became possible. Because the ship's mass was lowered rather than space itself being bent, this avoided the time dilation that would otherwise plague such speeds. With a mass effect drive a ship could traverse roughly a dozen light-years in the course of a single day's cruise.

A drive's maximum speed, and how long that acceleration could be sustained, varied with its exact type, and in general a larger drive could run at FTL for longer. Travel across space followed a simple profile of acceleration and deceleration: thrusters fired in one direction for the first half of a journey, then reversed for the second half so the ship could slow to a manageable speed for arrival, a vessel having to shed exactly as much velocity as it had gained. The drive also carried a built-in safety: it refused to fire if a significant object lay in the path of a planned jump, a feature inherent to its warm-up process and very difficult to remove.

The hazard of drive charge#

Element zero FTL drives accumulated a static electrical charge whenever a vessel spent time in FTL flight, and that charge grew steadily the longer the ship ran. Eventually it had to be discharged. The safe method was to release it into a planet's magnetic field for larger ships incapable of landing, or through direct surface contact for smaller vessels. Space stations and similar structures without a nearby planet were typically fitted with their own discharging facilities, the Citadel maintaining dozens of them.

If the charge could not be discharged, the consequences were dire. Left to build, it would eventually arc into the ship's own hull, with heat enough to fuse the bulkheads, destroy the electronics, and kill everyone aboard. Managing drive charge was therefore a routine and unavoidable part of any extended voyage under FTL.

Appearance and detection#

A ship under FTL looked very different to an outside observer. Light moved more slowly through ordinary space than through a high-speed mass effect field, so light entering the field was refracted, changing angle and separating into a spectrum. The greater the difference between the exterior and interior speeds of light, the greater this effect, with objects outside the ship appearing to redshift until they were visible only to radio antennas, while high-energy sources normally hidden to the eye, such as pulsars and the accretion discs of black holes, came into view. To an observer outside, the ship itself appeared blueshifted, its emissions carrying more energy than normal.

These optical effects had a practical military consequence. A vessel moving at FTL was visible at great distances, though its signature propagated only at lightspeed. Stealth systems that relied on managing a ship's heat emissions failed at FTL speeds, because the blueshift pushed those emissions into frequencies too high for the hull's heat sinks to capture. The speeds themselves were considerable: by the mid-2160s human starships could travel at least fifty times the speed of light, while the Reapers were believed capable of covering nearly thirty light-years in a day, roughly twice the pace of Citadel vessels.