(covers information from several alternate timelines)
This page contains information regarding Star Trek: Strange New Worlds, and thus may contain spoilers.
The Argus Array (full name: Argus Subspace Radio Telescope Array) was a Federation subspace telescope located in the Alpha Quadrant near the Gamma Trianguli, Alpha Majoris, Talos, and Setlik systems. In the 2360s, it was positioned at the edge of Federation space, three light years from Cardassian territory.
The Argus Array had been in service with Starfleet since at least 2259. That year, the location of this subspace telescope was labeled on a stellar cartography chart that was seen on the USS Enterprise's ready room viewscreen. (SNW: "Strange New Worlds", "Children of the Comet")
An unmanned structure, the Argus Array consisted of eighteen hexagonal subspace antennae clusters, each powered by an individual fusion reactor and all regulated from a central computer. It was capable of collecting detailed images of objects many light years away. (TNG: "The Nth Degree", "Parallels")
In different quantum realities, the Enterprise-D returned to the Argus Array in 2370 to investigate why it was not transmitting data. In these parallel universes visited by Lieutenant Worf, the cause of the array's shutdown was varied. In one, the Cardassians had reprogrammed the array to spy on Federation outposts; in another, it had suffered a simple mechanical failure. In one universe, the Cardassians had destroyed the array; in another, the Bajorans did so. (TNG: "Parallels")