Mass Relay

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 decades with only convential FTL drives.

Overview
Mass relays are built with two long, curved metal 'arms' with a set of revolving rings in between them, containing a massive, blue-glowing element zero core. The relays are made of an unknown but incredibly resilient material, the same material that the Citadel is built from. One of the relays even survived 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, are 'gravitationally anchored' to planets; 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.

Mass relays are believed to be indestructible by galactic society, but no known attempts have been made to actually damage or destroy a relay because they are the only means of long distance space travel and thus too vital to risk. Research teams however have calculated that if a large enough mass impacts a relay with enough force, the relay should not be able to withstand it. The consequences of destroying a mass relay are immense: as a huge mass effect engine manipulating massive quantities of energy, a relay could produce an explosion of supernova proportions.

There are two kinds of mass relay, primary and secondary.

Primary Relay
Primary relays can propel a ship thousands of light years but only link to one other relay, its 'partner'.

Secondary Relay
Secondary relays can link to any other relay over shorter distances, only a few hundred light years.

Citadel Law
After the Rachni Wars, space faring species of the Citadel Council 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 rift when the Turians found Coalition pioneers, ignorant of this Citadel Council prohibition, trying to open any Mass Relay they could find while exploring the relay network. This eventually leading to conflict between the Interstellar Coalition and the Citadel Council.

Coalition Law
The Interstellar Coalition at first saw the Mass Relay's as dangerous following the Xindi Conflict and until the 2350s had inplace the Relay Directives, which superseded all other standing orders and general directives and dictated that once the Relay had been detected the primary goal was to locate and shutdown any active Relay, if that could not be achieved, the device had to be destroyed by any means possible.

Normally a specially trained team was called in to deal with any situations involving the particle; if this team is not available, the Captain was authorized to deal with the situation by any means they deem necessary.

Dormat Relay
Many Mass Relays are currently dormant for unknown reasons, though they can be easily reactivated.

Origins
The mass relays, despite common belief, were not created by the Protheans but by the Reapers. The Protheans were merely one of many alien races to find the relays and the Citadel and take advantage of them. When the Reapers wiped out the Protheans, the asari were the next race to find the relays thousands of years later. Using the relays means that civilizations evolve along the paths the Reapers desire. However, the Protheans did have a keen interest in the relays, and managed to crack the secret behind their operation. This enabled them to build the Conduit before they were destroyed by the Reapers.

Tactics
The crucial choice for any attack through mass relays is how to divide the fleet for transit. The accuracy of a relay's mass-projection depends on the mass being moved and how far it’s going. Any long distance and/or high mass jump will see "drift". That is, a ship may be hundreds or millions of kilometers from its intended drop point, in any direction from the relay. Distance can't be chosen by admirals, but a relay is told how much mass to transit.

For example, if told to move a million metric tons of mass, the relay will scan the approach corridor, find four 250,000-ton freighters, and transit them together, maintaining their relative positions. A commander has the option of moving his fleet as one large, coherent formation that may be wildly off-position, or breaking it up into many smaller formations that will be individually closer to the intended attack point, but could be widely dispersed. Conservative assault doctrine holds that fleets should be moved en masse, maintaining concentration of force and reducing the chances of collision. The only time it is reasonable to split up a formation is during blockade running.

Relay Zero
The Citadel itself is an enormous, inactive mass relay leading to dark space, as well as the control center for all the relays, enabling the Reapers to sever travel between clusters. Its reactivation is, fittingly, more complex than that of an ordinary mass relay, requiring either a coordinated effort by the keepers or manual intervention by a Reaper.

Delphic Relay Network
The Delphic Relay Network was a rare isolated web of secondary Mass Relays, seperate and unreachable along the rest of the galactic Mass Relay network. Three-million years ago several dozen stars of varying composition and size were simulantiously destroyed and their collective energies poured inward via some sort of stellar manipulation. It was assumed the race attempting to do this was trying to destroy the Mass Relays in the Expanse of their era.

However the Reapers managed to halt this, by reconfiguring the Azati Minor Relay as a would be siphon to absorb all that energy and translating it through the other Relays in the Expanse on a never ending loop where it could never materialize. The imploding energy wave was frozen in its tracks, held in place by the Azati Minor Relay as the center of the loop, the rest of the energy loop forever cycling through the other relays in the Expanse. As a precaution, the Mass Relays in the Delphic Expanse were isolated from the galactic network at large, for fear that if the energy loop were ever disrupted it, it could decimate the entire galactic network.

A side affect of holding the energy of several dozen stars in a never ending loop was a bubble of thermobaric energy began to form around the Relays, attracted to the power but kept at bay by the gravity halos of the same Relays, creating the clouds that would soon isolate the Delpic Expanse from the rest of the galaxy.

Millions of years later the Reaper Monarch, encouraging the New Xindus Cooperative to begin expanding militarily for it to use them as a puppet force to invade the Citadel, reactivated a portion of the network, shifting the loop onto the remain half of the inactive Relays but keeping the Delphic Relays seperate from their galactic counterparts. The New Xindus Cooperative began a wave of conquest across the Expanse using the Relays and that soon brought them into war with the Interstellar Coalition, starting the Xindi Conflict of the 2150s.

The Expanse's orgins were unknown until theorized by Captain T'Pol during the final hours of the conflict, after studying the thermobaric clouds throughout the entire later stage of the war, along with recovered archeological texts from all over the Expanse, she managed to determine the nature of the clouds and their orgins.

She also theorized how to disrupt the Relay loop and during the Attack on the Azati Minor Relay disrupt the loop just long enough reverse the energy while dialing up the Relay's gravitional pull. The energy was enough to destroy the Relay's outright but damaged them enough that their own gravity halos caused everyone of them to implode.

Without the Relays, the thermobaric clouds had no energy to sustain themselves and began to rapidly fade, before finally the Expanse was no more and regular travel could resume to the outside galaxy.