A Starfleet deep space station near Ivor Prime that raised the alarm in 2373 when the nearby colony was wiped out, the first sign of the Borg attack on Earth.
Deep Space 5 is a Federation deep space station in Starfleet service during the late twenty-fourth century. It is known from dialogue rather than from any on-screen visit.
In the Next Generation episode Parallels, one of the quantum realities Worf slips through has the Cardassians secretly using the Argus Array to spy on Federation sites, Deep Space 5 among them, alongside Starbase 47, the Iadara colony and the Utopia Planitia yards.
In the film Star Trek: First Contact, Admiral Hayes tells Picard that Deep Space 5 has reported the destruction of the colony on Ivor Prime. The culprit proves to be a Borg cube heading for Earth, and the report opens the Battle of Sector 001.