Ultrawave communication is impractical beyond about 10 kiloarsecs; signal strength falls off rapidly, reaching 37% at 11.3 kpsc and 0% at 13.3 kpsc. Even before the Provincial Capitals were established in TE 37, it was apparent that a Galactic civilization needed relay points to boost signals.
In TE 70 (2223 CE), under the auspices of Imperial Centcom, six Ultrawave Relay Stations were deployed in a great equilateral triangle around the Galaxy. Relays Alpha, Gamma, and Epsilon were set at 1/3 of a Galactic diameter; Beta, Delta, and Zeta were at 2/3. Alpha was placed on a line directly connecting Terra to the Galactic Core. (map)
The Ultrawave Relays were enormous stations packed with the Empire's highest technology. Although crewed, they were constructed to be self-repairing and self-operating. Throughout the First Empire, they served perfectly; during the long war with the Patalanian Union, the Relays were considered strictly off limits by both sides.
Following the fall of the Empire, the Ultrawave Relays were ultimately abandoned, but continued to operate into the Interregnum. However, since none of the Relays was within the primary boundaries of a major political group, no one took responsibility for maintenance.
In 4723 CE, Relay Delta (Patala region) began developing problems; by the end of the year, it was off the air. A few expeditions were unable to repair the unit, but since the region continued to be served by Relays Gamma and Epsilon, there was no alarm.
In 5739 CE, Relay Zeta failed. The Credixian Imperium sent techs to look at it, but the region was in political turmoil and the Reichstaag feared that permanent Credixian presence would be too expensive, so turned down the authorization for repairs.
Relay Beta was destroyed during the Geled-Natal War in 5378; its traffic was automatically shifted to Alpha and Gamma, but still outlying regions of the Transgeled lost contact with the rest of the Galaxy.
Relay Alpha failed in 6484 CE; an expedition to repair it met with no success. With Alpha gone, most of the Sol sector was isolated.
In 6604 CE, Gamma failed, leaving Epsilon as the sole functioning Ultrawave Relay in the Galaxy.
Epsilon continued operating until it was replaced by the Second Terran Empire.