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

Paragravity

Modern human paragravity 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. 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. Early experiments with actual artificial gravity, first following the ZGene fiasco of the 22nd century and sporadic later attempts in the 23rd century, failed to produce both a reliable and power-economical solution, either being unstable or disproportionately power-hungry. These early gravity plates additionally lacked the inertial compensation benefits of later paragravity. As such, their adoption was never widespread, especially on ships, though a small number of Solar habitats continued to maintain them.

Prior to the development and widespread introduction of 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 a "stacked" deck layout, i.e. 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 0.4g and 0.75g. 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.

Study of Covenant gravity technology over the course of the Human-Covenant War has opened up new avenues for human paragravitic research, though for a time these would not be directly applicable to human paragravity systems as Covenant artificial gravity operates on entirely different principles. However, the Covenant showed that despite humanity's early failures, actual gravitic-based paragravity could be accomplished along with far superior local control and fine-tuning of the gravitic environment. Despite this, it would be decades before the UNSC would begin to adopt Covenant-style artificial gravity systems.

Contragravity

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. UNSC contragravity technology is originally based on the much earlier, failed attempts at paragravity in the 22nd and 23rd centuries. A CAA-sponsored corporate research group picked up this line of research in the 2350s, as part of a "blue skies" project to explore alternate uses for the technology. While the initial results were dissatisfactory, largely producing novelty applications later refined as the popular sport gravball, the UNSC as well as various corporate and university research groups continued to show interest. In the late 24th century, the first trials began with contragravitic "gravity cushions" used to provide additional lift for shuttles and transport craft. By the mid-25th century, such technologies were already being adopted by several types of craft. These were largely shuttles, dropships and other surface-to-orbit craft, though exceptions did occur. One of these was the decision to equip the Phoenix-class colony ships with contragravitic engines, massively improving their surface support capabilities. However, use on military combatant vessels remained minimal at the time. For a long time, most UNSC admirals were skeptical of the technology, seeing atmospheric operation as a gimmick with few tactical benefits for ships built for space engagement, while raising concerns about added mass, power drain and reliability.

Nevertheless, gravitic lift engines began to percolate throughout the Navy since the 2510s, first in small numbers which then gradually increased throughout the Human-Covenant War. Ships would typically only be fitted with the technology if atmospheric operation was deemed a priority, often for the sake of troop deployment, as was the case with the Charon-class frigate. The proliferation of contragravity suspensors within the fleet led to new modes of utilizing warships, including atmospheric precision strikes on ground targets and providing fire support for ground forces. However, this also imposes certain limitations on the use of the ships' weapon systems. Most frigate classes introduced into service by the mid-2500 were atmosphere-rated and fitted with contragravity generators by default. Some older ships were also retrofitted with contragravity systems around this time. The first new cruiser and carrier classes to receive full suspensor systems were introduced in the late 2560s.

Rather than relying exclusively on contragravity, many ships apply contragravity technology in tandem with conventional engine systems. Many colony ships, cargo transports and civilian passenger liners still continue to employ a gravitic assist engine for both additional lift and stability control while otherwise still relying on conventional engines for the most part. Many UNSC craft, such as D77 Pelican dropships or the D41 Cormorant, use a similar arrangement, lightening the strain and power drain on their thruster engines by applying a energy-intensive paragravity cushion. As paragravity technology has improved, so has its contribution to the overall lift. Post-war concepts for the next-generation replacement for the venerable but aging Pelican dropship rely largely on paragravity for lift while retaining thruster/hyperfan engines for maneuvering.

Aside from its application on ships and a number of industrial uses, for much of the 26th century human contragravity remained limited and unrefined, and it would not be applied as widely as within the Covenant until centuries later. In the civilian world, its most overt presence was less overt, mostly being found in highly specific applications such as gravball, which quickly became the most popular sport across much of the Human Sphere following its invention in the first half of the 25th century.

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. 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 Covenant standard for artificial gravity is 0.95g, which is maintained in much of the Tower Districts of High Charity's Golden City. Elsewhere throughout the city-station, gravity varies extensively, though most of the primary public areas are maintained at the same level. This is seen as a compromise between the comfort of the San'Shyuum and Sangheili, with the former preferring lower and the latter higher gravities. Most of the San'Shyuum estates and private residences operate at a gravity lower than this due to the species' frailty, though many younger San'Shyuum in particular hope to remain fit as long as possible by spending time in standard-gravity areas without the use of gravitic aids such as antigravity belts - even as this becomes an inevitability for them as they grow older. Following the Holy City's example, most ministerial ships use 0.95g as the standard for their internal paragravity. Some Peripate worldships and vessels prefer lower gravities, though often civilian stations and ships adjust gravity locally by district or deck. Due to their spindly physiology, Kig-Yar tend to favor low gravity, and frequently run their ships' paragravity at even lower than Eayn's 0.875g. This is especially true of spaceborn Kig-Yar, with the median for Kig-Yar habitats' gravity being around 0.49g. The various low-gravity adapted Kig-Yar groups known as Spanners might prefer ambient gravities as low as 0.1-0.2g. Despite Balaho's lower-than-standard gravity, the Unggoy can withstand higher gravities surprisingly well up to a point, owing to their robust physiology and anatomy. Still, most prefer lower gravities, and Unggoy habitats often operate in as little as 0.5g. Yanme'e, as lightworlders, tend to prefer gravities similar to spaceborn Kig-Yar or lower, typically around 0.3-0.5g. Despite their spacefaring status, the Yanme'e never developed artificial gravity natively as their need for it was less acute. Many Yanme'e habitats, particularly those in their home system, still eschew artificial gravity entirely.

The Jiralhanae are the exception to this trend due to Doisac's crushingly high gravity of 2.1g. Viewing their heavyworlder heritage as a matter of cultural pride, the Jiralhanae typically dislike spending time in low gravity, and when given the chance, often run their own ships at Doisac's gravity or close to it. When other species are present, typically as laborers and thralls, the Jiralhanae are forced to compromise on this as high gravities can be physically debilitating on Kig-Yar, and potentially lethal to San'Shyuum and Yanme'e. There are also groups of non-Doisac-born Jiralhanae who adapted to lower gravities in the species' ancient migrations and have subsequently lost considerable muscle mass and bulk over the generations can be considerably inconvenienced by Doisac's gravity.

In general, the Jiralhanae are somewhat exceptional in that they mastered gravitics comparatively early on, around the same time 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 and durable. Though many of its original applications were lost in the several Immolations that wracked the planet and the subsequent dark ages, select Jiralhanae tribes retain piecemeal know-how and industrial ability to manufacture certain types of gravity technology. Though most of these take the form of weapons and vehicles of war, antigravity generators can be found in unexpected places, such as antigravity chariots and carriages drawn by beasts of burden.