Orbital defense platform

An orbital defense platform (ODP), or orbital weapon platform, is an armed space station designed to defend a planet or other astronomical body, either from enemy attack or asteroids and space debris. Most human colonies maintain basic, magnetic linear accelerator- and missile-based orbital defenses; most of these are operated by the UNSC Aerospace Force or local civilian agencies. Important colonies are defended by arrays of weapon platforms with heavy Magnetic Accelerator Cannons capable of gutting Covenant capital ships, with many of these only being developed during the Human-Covenant War. All ODP types (like all space stations) have stationkeeping thrusters, are able adjust their orbits and even move about to some extent. However, they are very slow and sluggish, and most lack the capability to leave orbit under their own power. The thrusters used to counteract the recoil of the stations' MAC guns are powerful, but they are built to fire in short, highly energetic bursts, making them unsuitable for the sustained burns required to leave the orbit of a standard-gravity world. Moving ODPs throughout a system requires external tugs or thrust couplings, though the UNSC would also occasionally tow them using a cruiser or other large warship.

Although most orbital defense platforms are built for the task, the UNSC also made use of a number of improvised stations during the Human-Covenant War, as their demand grew and their ability to build them shrunk. Usually adapted from decommissioned capital ships that are too old, too badly worn, or too damaged for continued use, these have their slipspace drives removed and are stripped down to meet the needs of planetary defense. Originally used as system defense vessels, they gradually became less and less mobile as the conflict dragged on.

UNSC

 * Viery-class: Superheavy MAC platform powered by surface-based or ship-based generators, the Viery-class was originally commissioned during the Insurrection and later upgraded to augment its capabilities against the Covenant. The MAC gun on the Viery-class remains the most powerful kinetic weapon ever built by Humankind, but the class was plagued by various issues, including a reliance on beamed power, sluggish maneuvering due to its massive size, and the relative fragility of its structure, particularly the large rectenna surfaces used to capture the beamed power. As a result, Viery-class platforms were always few in number and considered obsolete after the introduction of the Moncton-class. Reach had twenty Viery-class platforms, while Earth's orbital defense array included 28.
 * Moncton-class: MAC platform introduced in the later years of the Human-Covenant War, the Moncton-class became standard over the larger Viery-class due to its more modern design and command-and-control subsystems and internal fusion reactor, removing the reliance on surface-based power plants. This came at the cost of performance; the MAC gun on the Moncton is considerably less powerful than that of the Viery. To compensate for individual platforms' reduced firepower, the Moncton-class ODPs are designed to work in battleclusters of three stations orbiting in close proximity, coordinated via modern networking systems. One of the Moncton ' s main shortcomings was its point defense, which was found to be lacking in key areas, allowing precision strikes by Covenant boarding craft to insert boarders onto the stations. After the war, the surviving Moncton-class platforms received refits to fix their most glaring flaws and continued to serve for decades onward.
 * Manila-class: The Moncton ' s direct predecessor, the Manila-class served as Earth's first orbital MAC gun array in the Insurrection era; Earth's last Manila-class OWPs were phased out in 2552 with the activation of the final Monctons, though they were found on colonies well into the post-war era.
 * Tanais-class: Light defense platform, often found on colonies.
 * Antioch-class: A commercial light defense platform, armed with a coilgun and a missile battery. Designed to operate in small clusters.
 * Torres Vedras-class: launched in 2570, the Torres Vedras-class OWP was designed as the successor to the Moncton-class, built on a similar operational schema but with superior power generation, sensor systems leveraging superluminal communications, improved maneuverability, and better point defense (including anti-plasma disruptor field generators). By the late 2570s, the Torres Vedras-class platforms had virtually replaced the aging Monctons over notable colonies.
 * Salamis-class: a makeshift ODP built from the stripped-down hulls of Marathon-class heavy cruisers.

Covenant

 * Silent Hymn-class: well-shielded installations armed with a single heavy plasma lance and a handful of pulse lasers.
 * Heavenly Oath-class: Classified by the UNSC as the CDX-class battlestation, these are small, prefabricated starbases hastily deployed in regions of strategic and tactical significance. Designed with the mindset that the Covenant's fleets will be on the offensive.