Orbital defense platform
From Halopedia, the Halo wiki
Introduction
An Orbital Defence Platfor is a small space station that hovers over a certain city on Earth. In the station are marines and a MAC gun, used for taking out Covenant ships. There is also sometimes a UNSC ship docked at the station used for a quick getaway or to engage enemy forces. In Halo 2, three stations are mentioned. Cairo Station, Malta Station and Athens Station. Also the first level where you encounter enemies in Halo 2 is named after the Cairo Station.
First Battle Of Earth
During the First Battle Of Earth, the stations proved a good defense against the Covenant with their MAC guns. However, the Covenant fleet brought bombs with them to destroy the stations. Both the Malta and Athens were destroyed, but the Master Chief was able to prevent the destruction of the Cairo station.
