Orbitor

An Orbitor is a broad classification of armed starship which was used prior and during the Interplanetary War. Originally used to describe early reusable spaceplanes, Orbitors were later strictly defined as any ship too large to operate within a planet or moon's atmosphere and too short-ranged and/or unreliable to make interplanetary trips without support. Such vessels were typically larger than maritime corvettes and were often multirole platforms designed for a wide variety of mission sets, from repair and refuelling to orbital fire support to ballistic missile deterrence. However, as the range of starships increased, this eventually referred only to ships which could not support their weight in an atmosphere.

Due to the significant expense in creating warfighting starships, Orbitors came to symbolise the impressive capabilities of any country's military. Despite this, their firepower was often far inferior to those of traditional maritime vessels due to the United Nations' enforcement of Space Armaments Regulations (SARs). These regulations limited gun calibres and missile payloads, and forbid nuclear weapons and other weapons of mass destruction. While diligently followed during the early decades of the twenty-second century, it would be steadily phased out during the mid- and late-2100s in favour of traditional maritime descriptors. The reasons for this included a difficulty in quickly deducing a given combatant's capabilities, the desire of many nations to disregard the SARs, and the simple fact that few ships were now restricted around the orbit of a single celestial body. Upon the formation of the United Nations Space Command, Orbitors only referred to localised police craft before fading into obscurity.

Post-Jovian Orbitors or Gunboats
During the Siege of the Jovian Moons, existing models of Orbitors found themselves woefully unprepared for fighting a guerrilla war against rebel forces. This was not because of their power, as their heavy armour and large stockpiles of missiles left them almost invulnerable to the improvised spacecraft that they fought against. Rather, they were simply too slow and numbered too few to keep a secure hold over their geosynchronous regions, which allowed rebels to routinely run the blockades, spread the violence across the Jovian planetary system, and often flee long before the nearest warship could arrive. As a result, naval architects were encouraged to create a fleet of smaller, faster ships that could better support their squadron leaders.

Post-Jovian Orbitors were universally smaller than their predecessors, with a tonnage of no more than 6,000 metric tonnes and a length that struggled to exceed 100 metres. This crucial change meant that crew requirements and construction times were slashed by at least half on average. The most common configuration followed that of the first Post-Jovian Orbitor, the UNSC Vengeance. This combined an all-missile complement as their primary armament, with up to two low-calibre naval guns for close-range attack, a midsection hangar capable of handling not much more than a dropship or two space fighters, high-performance propulsion system, and finally a heavily-armoured hull that matched existing Orbitors. Heavy missiles remained within forward-facing cells, but most of the payload now resided within smaller missile pods that pot-marked the main body. This resulted in a high-speed pursuit ship with a good range on its weapons, while being difficult to hurt. Unfortunately, Post-Jovian Orbitors returned to their short-ranged roots because they did not have much in the way of consumable storage.

The technological changes present in Post-Jovian Orbitors were many. Because it was proven that calibres already in service were overkill against armed freighters, most naval gun rounds were replaced with tungsten shells measuring 102mm, 127mm, and 154mm in size. Although they were less effective against armour, all three had an average velocity that was higher than existing shells. The propulsion systems on new Orbitors was overhauled to incorporate more efficient plasma drives over traditional ignition engines, while longer-range warships used ion engines paired with a booster rocket.