Mass Relays

Important Note: The Council has prohibited blind activation of unmapped mass relays. Anyone found attempting activation of unmapped relays will be subject to severe criminal prosecution.


Mass Relays are mass transit devices scattered throughout the galaxy, usually located within star systems. They form an enormous network allowing interstellar travel. Hailed as one of the greatest achievements of the extinct Protheans, a mass relay can transport starships instantaneously to another relay within the network, allowing for journeys that would otherwise take years or even centuries with only FTL drives.

Mass relays consist of two fifteen-kilometer long curved metal arms surrounding a set of revolving, gyroscopic rings five-kilometers across. These rings contain a massive, blue-glowing core of element zero. The relays are made of an unknown but incredibly resilient material, the same material that the Citadel is built from, and are protected by a quantum shield that renders them nearly impervious to damage by locking their structure in place at the subatomic level. They are even capable of surviving a supernova’s wake without being damaged. They are “cold” objects that don’t emit heat or radiation, unlike starships, making them difficult to find if their position changes. Some relays, like the Charon Relay, are “gravitationally anchored” to celestial bodies; others appear to be out in space and are carefully tracked.

Mass relays function by creating a virtually mass-free “corridor” of space-time between each other. This can propel a starship across enormous distances that would take centuries to traverse, even at FTL speeds. Before a vessel can travel, the relay must be given the amount of mass to transit by the ship’s pilot before it is moved into the approach corridor. When a relay is activated, it aligns itself with the corresponding relay before propelling the ship across space.

There are two kinds of mass relay, primary and secondary. Primary relays can propel a ship thousands of light years but only link to one other relay, its “partner”. Secondary relays can link to any other relay over shorter distances, only a few hundred light years. After the Rachni Wars, Citadel species won’t open a primary relay without knowing where it links to, in case they run into another powerful and hostile species like the rachni. This caused a conflict between the turians and the humans when human pioneers, ignorant of this Citadel Council prohibition, were discovered trying to open any mass relay they could find while exploring the relay network, eventually leading what humans now refer to as the First Contact War.

Many mass relays are currently dormant for unknown reasons, though they can be easily reactivated. An example from recent times of this is the human discovery of a Prothean data cache on Mars, which led the fledgling race to a mass relay encased in ice and orbiting Pluto. previously thought to be a moon called Charon, which the Charon Relay was eventually colloquially named after.

A small-scale mass relay is present within the Citadel’s Presidium, known as the Relay Monument, and prior to the attack on the Citadel it was believed to simply be a piece of Prothean artwork depicting their achievement; it was interpreted as either a symbol of Prothean vanity, expressing the relays as their means to build a galaxy-wide empire, or possibly as a symbol of galactic unity, which the relay network also embodies.

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Mass Relays

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