Wormhole relay station

The wormhole relay station was a subspace relay station that allowed communications from the Alpha Quadrant to pass through the Bajoran wormhole into the Gamma Quadrant between stardates 48543.2 and 50564.2.

Historical Background
Although communications through the wormhole were possible, it was unreliable and required the wormhole to be open while the transmissions occurred. Some attempts were made in 2370 to produce a reliable communications network that traversed the wormhole, but due to the wormhole's high interference, which consisted of unstable subspace carrier waves and high phase variances, the signal was not strong enough to pass through. Subspace communications that bypassed the wormhole could take over twenty years to reach the Gamma Quadrant. 

The disastrous First Contact between the Dominion and the Federation created a growing need to have a reliable communications conduit to the Gamma Quadrant so that Dominion activity could be monitored.

In 2371, the Bajorans put behind fifty years of hatred towards the Cardassians when Vedek Bareil, under the auspices of Commander Benjamin Sisko, brokered an historic peace treaty between the Cardassian Union and Bajor which was signed by Legate Turrel and Kai Winn. This treaty paved the way for the wormhole relay station to be built. 

Construction and Deployment
The first joint Federation-Bajoran-Cardassian effort under the new peace treaty, called the Wormhole Comm Relay Project, was to create a Gamma Quadrant relay station to aid communications between the two distant quadrants. The Cardassian government sent three of its scientists, Ulani Belor, Gilora Rejal, and Dejar, to participate in the effort. However, former Vedek Yarka warned the Emissary of the Prophets, Benjamin Sisko, that the Cardassian involvement in the project would lead to the destruction of the wormhole according to Trakor's Third Prophecy, which predicted that three vipers would destroy the Celestial Temple. Despite his objections, though, Commander Sisko ordered the project to proceed because the Kai and Vedek Assembly had already agreed on the project.

In accordance with the project plans, the USS Defiant (2370) positioned the signaling satellite at the Bajoran end of the wormhole and deployed the relay station on the Gamma Quadrant side. While testing the relay station, the crew discovered a comet whose trajectory would pass close to the wormhole. Major Kira saw this as a support to Yarka's claim about the prophecy.

When the first test of the relay produced no results, the team conducted a second test using a different subspace frequency. However, the second test inadvertently opened the wormhole, which increased its gravity and set the comet on a collision course with the wormhole.

Simply destroying the comet could have created multiple fragments, so Chief O'Brien modified the phasers of the Defiant to generate a wide beam that would encompass the entire comet and destroy it evenly. When the Defiant fired her phasers, however, a standard burst was fired instead, causing the comet to split into three pieces, all still on course for the wormhole. O'Brien's examination of the weapon system suggested he made a mistake, one that even a first-year engineering student wouldn't make. Gilora then informed him that Dejar was a member of the Obsidian Order and that she had sabotaged the phasers in an effort to undermine Cardassian-Bajoran relations by trying to let the relay project fail. It seemed the prophecy would be fulfilled just as Yarka had said.

To save the relay project from a disaster, Sisko positioned a shuttle between the three comet fragments in an attempt to contain them while they passed through the wormhole. Except for a small amount of silithium leakage from the comet, he and Kira successfully contained the fragments and kept the wormhole intact. More importantly, the silithium that was inadvertently released during the procedure created a small subspace filament in the wormhole, large enough for the wormhole relay station to work. Sisko had fulfilled the prophecy, although not in the way Yarka explained it, and ensured that the wormhole would never close again. 

Logistics
The wormhole relay station consisted of a Starfleet-produced signaling platform and was positioned two kilometers from the wormhole entrance. It also contained a Cardassian transceiver, devised by Ulani, that was powered by a Starfleet power grid. The transceiver assembly sent a subspace carrier wave through the wormhole to a second transceiver, located on Deep Space 9.

The transceiver used soliton pulses, carefully tuned to eliminate any phase variance below 0.005% to minimize the impact on the wormhole. Ulani and Gilora improved the station's signaling array so it could accommodate the new transmissions (and removed O'Brien's secondary backup of the station's system in the process); however, the simulations showed that transmission frequencies in the delta band would not work, and the theta band frequencies could create a subspace inversion. In essence, it was the subspace filament that allowed transmissions to occur; the filament (created when the comet's silithium reacted with the wormhole's ambient radiation) was a thin trail that acted like a subspace carrier wave and helped to carry transmissions through the bends of the wormhole. 

Service record
The subspace relay station played an important part in communications while Starfleet explored the Gamma Quadrant.

In Julian Bashir's coma-induced reality created by the Lethean Altovar, a simulation of Chief O'Brien managed to communicate to the outside using the relay station. It revealed the voices of Jadzia Dax and Sisko in the real world, trying to revive Bashir from the telepathic damage caused by the Lethean. 

When Enabran Tain was about to destroy the homeworld of the Founders, Starfleet ordered Sisko to stay put and protect Bajor. Sisko, though, wanted to rescue Odo, who was being held captive by Tain, and decided to pursue him. If Sisko found any Dominion forces coming through the wormhole, he would warn the Alpha Quadrant using the communications relay. 

Before General Martok invaded Cardassia and started the Federation-Klingon War (2372-73), he was ordered to protect Deep Space 9 in event of an attack by the Dominion, who had placed Changelings throughout the Alpha Quadrant. Captain Sisko politely refused the offer for help, citing the fact that the communications relay picked up no Jem'Hadar activity near the wormhole. 

Lieutenant Arriaga, under orders from Admiral Leyton, attempted to mislead Starfleet into thinking the Dominion was sending cloaked ships to the Alpha Quadrant. He did so by attaching a subspace modulator to the communications satellite. The modulator had the effect of making the wormhole open and close at random. 

When O'Brien was convicted of spying on the Argrathi government, the Argrathi communicated to the station via the wormhole relay. 

Bashir used the relay station a number of times during his individual missions in the Gamma Quadrant, such as when he tried to cure the Jem'Hadar of their ketracel-white addiction on Bopak III, and when he cured the Teplans of the Blight. 

When Sisko, Worf, Jadzia Dax, Muñiz and O'Brien were trapped in a Jem'Hadar attack ship on Torga IV, Sisko used the communications relay to request the services of the Defiant. 

The relay station's most useful mission came when Worf and Elim Garak took a runabout to locate Tain, who was captured by the Dominion after his failed attempt to destroy the Founders' homeworld. When they found a Dominion fleet hiding in a nebula close to the wormhole, Worf managed to send a message to the relay and warned Deep Space 9 of the impending invasion. The relay's primary mission (to detect when the Dominion would invade the Alpha Quadrant) had been fulfilled.

With the message received, the wormhole relay station (and its associated outposts) were disabled by the Dominion fleet. 

Background information

 * The relay station model was a minor modification of the Amargosa observatory model from . The prop master shortened the two long pylons, removed the ropes previously attached to the antennae, and modified the central probe to create the appearance of a dish. The relay station's only appearance on screen was in the episode.
 * In, it appeared that the relay station was still in operation and not destroyed. The crew created a probe that contained goodbye messages that they launched, which emitted a Starfleet signal that contained the coordinates of the probe. Sending a signal in Dominion space would have only made sense if the relay station was still active.
 * The Dominion was able to communicate with the Gamma Quadrant listening posts in, but it is not clear whether they had re-used Starfleet's wormhole station or created their own relay.