Orbital defense platform
From Halopedia, the Halo wiki
Introduction
An Orbital Defense Platform is a small space station that is (in theory) in geosynchronous orbit over a city on Earth for which it is named. On board the station is a small contigent of Marines, apparently as a defense force in the event of an enemy boarding. The station's main purpose and feature is its Mark V "Super" MAC gun, which is capable of destroying a Covenant ship with a single hit. The station also has two docking spaces for UNSC ships, apparently avaliable to evacuate station personel or for other miscellaneous activites. In Halo 2, three stations are mentioned; Cairo Station, Malta Station and Athens Station. The first level you are in combat in Halo 2 starts on Cairo Station, for which the level is named.
First Battle Of Earth
During the First Battle Of Earth, the stations proved to be an excellent defense against the Covenant with their MAC guns. However, the Covenant fleet brought bombs with them to destroy the stations from inside. Both the Malta and Athens were destroyed, but the Master Chief was able to prevent the destruction of Cairo station.
