Lagrangian Point satellites, also called Lagrange Point satellites or simply Ancient satellites, were spaceborne weapons platforms created by the Lanteans and put to extensive use during their war with the Wraith.
Though nearly as large as a Goa'uld Ha'tak, these satellites have relatively little internal space, with only a control room accessible via an Airlock capable of docking with a single Puddle Jumper. Its power requirements are also fairly low, to the point where its primary weapon could be run using a single Naquadah generator. Each satellite carries one Lantean Beam Cannon, and through one continuous shot, it is able to split a Hive ship in half. It was stated that this weapon would be more than capable of destroying at least three Hive ships when fully charged. Whether that is the full extent of the satellites armament, and whether it had any defensive measures for protection, is unknown.
The charging rate of the weapon is rather slow, but is likely that the capacitor would refill significantly faster if a more powerful energy source, such as a Zero Point Module, was attached to it (assuming a capacitor would even be needed, as a stronger power source would likely be able produce enough power to fire the weapon almost immediately). (SGA: "The Siege, Part 1")
Several of these satellites were placed throughout the Lantean system, though most were destroyed by the Wraith during their march towards Atlantis. At least one such satellite was located at one of the system's Lagrangian points, and was later discovered by the Atlantis expedition; it had suffered some damage though, and its power supply was depleted. When the Wraith sent three Hive ships to destroy the newly reinhabited Atlantis once and for all, a three-man team from Atlantis managed to reactivate the satellite and used it to destroy one of the three Hive ships. Unfortunately, the repairs on the satellite didn't hold, rendering it offline, and the remaining Hive ships destroyed the satellite before the problem could be fixed, killing Dr. Peter Grodin, one of Atlantis' finest scientists, in the process. As witnessed, he was very brave, caring more about the people of Atlantis and the City than his own life. (SGA: "The Defiant One", "The Siege, Part 1")