Gravitics

Gravitics is the science of gravity manipulation, as well as the field of technologies concerned with its application. The two most common applications of gravitics are paragravity, artificially-generated fields which simulate the effects of gravity on starships, stations or low-gravity worlds; and antigravity, fields designed to partially or fully nullify the effects of gravity for a given area or piece of matter. As these effects are functionally the inverse of one another, the technologies used to achieve them are often related. In addition to its more obvious uses, gravity manipulation has numerous industrial, infrastructural and scientific applications. More exotic applications of gravitics include gravity-based propulsion (such as the Covenant's repulsor engines) as well as gravitic defenses and weapons, and even the Covenant's active camouflage devices.

Terminology

 * Antigravity: Generic term for technologies designed to counteract the effects of gravity. Often shortened to AG.
 * Centgravity: Centrifugal gravity; the illusion of gravity achieved through centripetal force acting on the inner side of a spinning drum or "carousel". Also known as spin gravity.
 * Contragravity: See antigravity.
 * Gravity envelope: The self-contained paragravitic environment of a ship or station.
 * Paragravity: catch-all term for artificially-generated pseudo-gravity fields. These are often used to create more comfortable environments on starships, space stations and habitats, and colonies on low-gravity worlds.
 * Periplate: Short for "perimeter plate" or "peripheral plate"; secondary gravity plating used on human ships and stations.
 * Repulsor: An antigravity device, often one used in propulsion-focused contexts.
 * Suspensor: An antigravity device, usually focused on levitating an object or reducing its effective weight relative to the ambient gravity.
 * Thrust gravity: The illusion of gravity achieved by acceleration. Nullified by most paragravity systems.

Humanity
Human gravitics has its roots in the 24th century, though it has taken up until the 26th for the century to mature and truly percolate throughout human civilization. The earliest and most widespread use of gravity technology is paragravity. Despite its name, human paragravity in its most widespread form is not true gravity per se, but rather a synthetically-generated pseudo-inertial force which mimics its effects.

Prior to the development paragravity, most ships used either spinning carousel sections to generate simulated gravity via centripetal force, or relied on a continuous application of thrust from the ship's main drives to provide a semblance of gravity. As such, spacecraft were traditionally built with their decks perpendicular to the main trust axis, similar to a skyscraper. Up until the 25th century, paragravity generators were massive and power-intensive, and thus largely restricted to surface colonies and stationary habitats. On starships, they first saw use on civilian vessels for the purposes of comfort. In the early days, paragravity was relatively inefficient and would only be used when the ship was coasting, and in conjunction with thrust gravity to increase its effects. On military ships, paragravity is a relatively recent addition; by the 25th century, it was still common to only install paragravity plating in small sections of the ship, and even many of the ship classes in service during the Human-Covenant War would retain vestigial spinning sections, albeit often used in tandem with paragravity plating.

A secondary advantage of paragravity is inertial compensation: because the gravity plating effectively creates a self-contained inertial environment, it also nullifies the effects of acceleration on the crew. This has the obvious advantage of allowing ships to accelerate more intensely and perform maneuvers more freely without risking the crew's safety; even so, rapid course changes can still sometimes be felt inside the ship. The effect was later discovered to work even more effectively and reliably with the paragravity gradient perpendicular to the main axis of thrust, which gave rise to the thrust-parallel deck layouts used in most modern UNSC ships by the 25th century. By the mid-26th century, these layouts had largely replaced the older, skyscraper-style deck arrangements, though some manufacturers continue to use hybrid designs.

Gravity plates could also double as defensive devices or weapons against boarders when turned on a higher power setting; an increased paragravity field can inconvenience, incapacitate, or even kill any intruders in a ship, station or colony. However, an enemy force could also infiltrate a ship's computers and turn the gravity plating against its own crew, a scenario which occurred several times in the early days of human paragravity. Because of such concerns, coupled with the potential risk of power surges inadvertently creating intense gravitational fields, most modern paragravity devices are built to be incapable of exceeding 1g; even then, they are rarely used at full power, normally being kept at between .4g and .75g. However, many older devices, some of which operate on slightly different principles, lack such safeguards and are considerably less reliable, though they continue to see use by various independent and insurrectionist groups, particularly due to their versatility as defensive devices.

Modern UNSC paragravity systems are twofold. The first component is a set of pseudo-gravity generators (usually one or two, placed in both ends of a ship, but sometimes more in the case of larger ships or stations). These generators project a gravitic field within their area of effect; this is the main paragravitic environment responsible for the inertial compensation. The second component are the gravity plates, which further orient, shape and amplify the gravity field locally. These are usually known as periplates, which is short for peripheral plates or perimeter plates. Every deck usually has them for stability, but a single set is sometimes enough depending on the size of the area being covered. The periplates are commonly designed to run on a low power setting in unoccupied sections of a ship or station, and only activate when necessary, usually when crew members are present. The twofold arrangement, invented around the turn of the 25th century, made paragravity much more efficient, reliable and robust; previously, every gravity plate had to be installed with its own gravity-generating mechanism, which made the early grav-plates highly complex and maintenance-heavy, in addition to their known reliability issues.

The UNSC made several strides in paragravity technology by studying Covenant gravity technology over the course of the Human-Covenant War, and paragravity generators installed on late-war and post-war ships are considerably more power-efficient and reliable than their pre-war counterparts.

UNSC contragravity is less mature than paragravity, having only truly taken off over the course of the 26th century. This is largely because it is considerably more challenging to achieve; whereas paragravity is not true gravity manipulation but rather a synthetic imitation of it on an extremely localized scale, antigravity technology must properly counteract the effects of gravity in order to work. One of the most dramatic applications of contragravity is on certain types of UNSC warships, largely on the lower-tonnage end of the scale. Larger ships can be fitted with the technology if atmospheric operation is deemed a priority, often for the sake of troop deployment, as was the case with the refit Phoenix-class support vessels. By the mid-2500s, many newer frigates in particular were rated for atmosphere, though not all were fitted with contragravity generators by default as the system's components remain expensive, take up space, and add a fair amount of extra mass. In many cases, the applications of contragravity are more subtle; war-era Pelican dropships or the D41 Cormorant, for example, use a gravitic assist engine for both additional lift and stability control while otherwise still relying on conventional engines for the most part.

The Covenant
Covenant gravitic technology is sophisticated and ubiquitous, seeing use in a wide range applications from the mundane to the high-end. The paragravity used on their ships is highly versatile, and local gravity gradients can be configured in highly variable directions; though most Covenant warships opt for a largely uniform gravity environment, the gravity manipulation used on some of their space habitats can be quite imaginative. Their main spacecraft propulsion is evidently gravity-based, and most of their ground vehicles utilize contragravity and repulsor mechanisms for locomotion. Repulsor engines used in ministry starships emit both gravitational and antigravitational for movement. Gravitic suspensors are also used to support otherwise impossible structures, and gravity bridges, conduits and lifts are widely used for transportation, all the way up to surface-to-orbit distances. Artificial gravitational lensing fields are used to bend lights around objects to hide them from view, or in telescopes, mirrors and even superluminal communications systems. Gravitic manipulation also forms a key component of Covenant plasma and particle beam emitters as well as select other types of directed-energy weaponry, which often forgoes physical lenses in favor of gravitic lensing. Covenant fusion reactors are also suspected to use gravitational confinement both to achieve and contain the fusion reaction as well as capture the neutron flux to provide power.

The Jiralhanae are somewhat exceptional in that they mastered gravitics before they mastered nuclear power and rocketry. This was partly a byproduct of Doisac's high gravity, which prompted the Jiralhanae to look for solutions to counteract its effects early on. Native Jiralhanae gravity technology is crude but effective; though the secrets to its manufacture were lost in most parts of Doisac by the First Immolation and its aftermath, many functional examples of the technology remained by the time of the species' assimilation into the Covenant over a millennium later.