In the far future, Earth was no longer able to sustain life on its surface. Because of that, huge satellites called "Near Orbitals", were designed and built for people to live on. In order to protect themselves, mankind formed a group called the Near Orbit Vanguard Alliance.
The Near Orbit Vanguard Alliance is Earth's best armed forces unit, equipping its marines with state-of-the-art technology such as Mobile Armoured Suits and AI advisors. As such, they not only protect Near Orbitals what with apparent alien threats such as the Xenos, Judgers and the Volterites. They act as protectors of humanity's best interest, answering to the Terran government. In N.O.V.A. 1, marines are stationed on the Colonial Pride and, also at the Epsilon Bunker and Mining Facility (although those at the mining facility were infected by Xeno Parasites) on New Ceres.