Habitat

A habitat, colloquially shortened to hab, is a sealed station designed for civilian habitation, either installed on a planet's surface or built as their own space stations.

Human
Humanity makes extensive use of habitats. While terrestrial colonies are now widespread in the 26th century, a significant portion of the human population still live in pressurized installations and space stations. Early ventures into extraterrestrial habitation on Luna, Mars and the Jovian Moons were dependent on sealed habitats. Even today, a number of fairly established inner colonies are either collections of domed cities, sealed arcologies, underground warrens, space habitats or habitat-aggregations, as their low habitability rating prevents economical terraforming. The exact design of habitats vary, as while some were purpose-built structures, others started out life as mined-out asteroids.

Unlike the Covenant, humanity's significantly less time with slipspace technologies meant that most of their habitats are effectively limited to the star systems they were built in. While they do have limited maneuvering capabilities for stationkeeping and emergencies, they are inherently fragile and unable to withstand the stresses that come with slipstream transitions. The few habitats which do have a capability for cheaply mounting a Shaw-Fujikawa engine incorporated this feature into their original designs, and are typically much younger than the vast majority of stations in existence.

The largest collection of habitats were all consolidated within the Sol system. The first were constructed in the 21st century in the Golden Age of Space Colonization, fueled by the gold rush into the system and the subsequent need for a long-term human presence in space. Because the early human space age lacked the sophisticated terraforming technologies of even the 24th century, space habitation was only possible in pressurized installations. These were generally clustered around the Earth, Mars, Jupiter, and Saturn orbital zones, although this wasn't the rule and small trading outposts had been established all throughout the system. Because of their cost, smaller habitats were generally preferred, but regulations later mandated the installation of some form of large space in order to combat cabin fever suffered by their populations. However, some Martian and Jovian populations in particular got used to their home installations' cramped spaces over time and took their lifestyle as a matter of pride; on Europa and Ganymede, such groups are known as Scuttlers. Some of them would later go on to colonize extrasolar worlds with no terrestrial environments most others would not contemplate settling in despite natural riches such locations often hold.

After the Domus Diaspora began, many of Sol's once-bustling orbital habitats emptied and their colonies effectively died out as their inhabitants moved on to greener pastures in other systems, with only the most established, well-off, and long-term colonies sustaining themselves throughout the exodus. Real-estate prices on many of the Solar habitats plummeted and by the late 25th century, wealthy citizens could purchase entire habitats for their own use. The UEG and private actors found various uses for the abandoned Solar habitats, including agriculture, entertainment and miscellaneous novelty uses such as sports and military training. Many people continued to live on habitats even around Earth, but mostly for specific cultural or commercial reasons.

Outside the Sol system, significant orbital neighborhoods arose even around colonies with Earth-like qualities, due to various needs to work in space or conduct industrial operations that are either expensive or not possible in anything but a microgravity environment. Such industries include heavy-duty shipyards and various types of specialized manufacturing; long-term workers usually live aboard habitats adjacent to the orbital shipyards, and as of the 26th century, corporations are virtually mandated to provide a certain amount of open living space for their employees. In addition, large orbital ports often double as habitats for both the businesses operating there and for transient residents, housing hotels and other forms of short-term housing for people awaiting to move on within several days, weeks or even months, depending on the presence of terrestrial worlds in the system.

Types

 * Cylinder habitats — based on Gerard O'Neill's classical Island Three concept and relying on spin gravity on their inner surfaces. Many different sizes and variants exist, usually with two or more counter-rotating cylinders or "drums" integrated into a single structure to provide balance. Also known as O'Neills, or spindles, especially when elongated and containing more than one habitable section. May either have enormous windows that open up into space or be fully sealed, with some having semi-holographic artificial skies. Usually disorienting for newcomers, and some never get used to the curved sky.
 * Segmented cylinders — A predecessor of sorts to the full-fledged O'Neill, consisting of self-contained, linear habitation modules arranged in a circle around a central hub and wheel structure. Easier to compartmentalize from micrometeorite impacts and disasters than single-chamber cylinders, but have less internal space.
 * Carousels — Stations based on the Stanford torus model or smaller classical space station concepts. Like O'Neill cylinders, rely on spin gravity and may feature one or more separate "wheels". Usually structured like a literal wheel, with spokes leading from the outer carousel to a central hub, which typically houses the main docking as well as control facilities. Some such stations include more than one wheel, as well as additional structures for functions like hydroponics, etc. Habitation sections may also be compartmentalized for emergencies. Many variants exist.
 * Rocks — habitat-stations built into asteroids. Traditionally use a cylinder- or drum-style design embedded into the asteroid, rather than burrowing warrens into and spinning the asteroid itself, as most asteroids are too fragile to reliably spin up. Since the advent of artificial gravity, have shifted to more free-form inner layouts with caverns often built into the asteroid itself, easily expandable when necessary. Most common habitat type, and numerous variants exist. Many feature artificial skies.
 * Bowls — Habitats designed to provide an approximation of gravity on low-g bodies, such as Luna and the Jovian Moons, by spinning a bowl- or funnel-shaped structure with habitation zones on the inner walls. Similar to a cylinder habitat but with tapering walls. Often built above the surface or embedded into it (e.g. in a crater). Challenging to engineer, disorienting to their inhabitants and often found not worth the effort; not many were built, and the design was phased out by the advent of artificial gravity.
 * Arcologies — Self-contained habitation complexes on a planetary surface; also exist in non-sealed form on worlds with breathable atmospheres. Colloquially known as "arcos".
 * Warrens — Tunnel-based habitats first built into the lava tubes of Luna and Mars as well as the ice sheets of Europa and Ganymede, some would later become quite elaborate and imaginative in their use of space. The Jovian ones in particular are usually based around a deep central bore hole with numerous smaller caverns radiating around them into different directions. May feature artificial skies.

Notable habitats

 * Goddard Station — Once known as the "Ellis Island of space"; the first proper habitat station built by humanity over Earth from Lunar resources to facilitate the colonization of the Solar System.
 * Phobos — Mars' closer natural satellite and primary orbital port; largely hollowed out and urbanized throughout. After plans to convert the second moon, Deimos, into a massive intrasolar cargo transport or a slower-than-light colony ship fell through, Deimos was turned into the orbital counterweight for the Tharsis industrial heavy-lift array.
 * Niven Station — The largest spin-gravity station in human space, orbiting Circumstance. Multi-wheel carousel design.
 * The Swarm — A conurbation of numerous habitats in the Eta Cassiopeiae system, primarily supporting industrial efforts such as asteroid mining and shipbuilding along with commerce.
 * Kaulua Spindle — A single-axis multi-cylinder type habitat in the Sirius system originally founded as a hub for scientific and industrial operations in the system.
 * The Rubble — An independent rock-conurbation built in the gas giant Hesiod's trailing trojans in the 23 Librae system. Used as a refuge by Madrigali citizens, destroyed in 2535.
 * Eridanus Secundus — A warren-based rock habitat in the Eridanus Asteroid Belt. Used as a base of operations by local secessionists, later served as a hideout for refugees from Eridanus II. Destroyed in 2552.
 * Station Jefferson — A trade port and minor habitat in the Eridanus Asteroid Belt once used as an Insurrectionist hideout.

Covenant
Covenant habitat types are myriad. Because the Covenant have had access to advanced gravitics for millennia, along with sophisticated materials science, their habitat designs are less constrained by restraints such as having to produce gravity by spin. Many are also mobile and capable of slipspace travel, doubling as worldships; the most notable of these being the holy city High Charity.


 * High Charity-type — Many Covenant habitats and worldships emulate the overall design of the holy city, itself loosely based on the silhouette of the Forerunner Fortress-class vessel Deep Reverence the San'Shyuum encountered in their home system. Some of these are built into asteroids, with a long tail sticking out on one side, though they may eventually morph into a different overall design as more elements are added (e.g. a second "tail" on the other side).
 * Baubles — A type of spherical or spheroidal Covenant space habitat, sometimes mobile, with artificial gravity on most of the inner surface and lighting provided by a central plasma ball or shaft. Baubles range in size from under a kilometer in diameter to twenty kilometers or larger, though the vast majority fall within the sub-ten-kilometer range.
 * Ring-shrines — Space habitats built to emulate the "Sacred Rings" of the Halo Array, albeit on a much smaller scale and with different proportions. Several variants exist; some are smooth bands while others have "spokes" for various logistical functions, including hangar bays, engines, etc.
 * Chandelier-cities
 * Helix-worlds
 * Orbital rings — Logistical structures that often also feature habitation facilities along their length.
 * Sky-citadels, Suspensor platforms & Orbital spires
 * Droplets — Droplet-shaped structures with habitable inner sides and a docking/hub structure in the tapering end. Sometimes paired with another, mirrored droplet (Unyielding Hierophant-type design)
 * Rock habitats — Popular among Kig-Yar in particular, who pioneered their use and design in their home system.

In addition to these recurring types, many Covenant habitats are unique in design and do not fit a particular category.