Icarus Fall Dictionary (IF)

Hard Science-Fiction Setting

There are many terms in the Icarus Fall setting that require explanation. Some are general space-flight terms, others are specific to the setting.

Acceleration

The rate of change in a spacecraft's velocity. In practice, this determines how quickly you can get anywhere and how much punishment the crew takes. Measured in meters per second squared or in Gs. Long burns at low acceleration are standard for interplanetary hauls. Often casually termed “speed.” Compare Delta-V, Earth Standard Gravity.

Accelerator

A fixed mass driver used to hurl cargo into new orbits using a series of magnetic coils. Accelerators range from small ore launchers in the Belt to massive facilities capable of sending kilotons toward the inner system. Those mounted on asteroids require regular station-keeping to counter recoil.

Albedo

The fraction of sunlight a surface reflects. Dark bodies have low albedo and absorb heat faster; high-albedo bodies reflect more light, heat up more slowly or barely at all, and can be spotted more easily.

Artificial Gravity

Any method of simulating gravity in space: rotation (spin habs) or acceleration (in spacecraft). Acceleration is only possible for a limited time due to constraints of Delta-V and Reaction Mass, making rotation the dominant form. All currently inhabited places except Earth and Venus have problematically low gravities, so long-term health depends on Artificial Gravity.

Aquatic

Submersion environments in water or other liquids; covers maneuvering, buoyancy control, thermal management, and respiration (natural or assisted). Applies from shallow basins to abyssal/high-pressure oceans.

See also: Environmental Specializations, Microgravity, Low Gravity, Earth Standard Gravity.

Baseline

Official term for an unmodified human (no major phenotype rewrite or cybernetic augmentation). Neutral in policy and technical documents, but can be used as a slur in casual speech. Common slang: unmod, stock, natural (neutral to mild), meat or pure (derogatory). See also: Posthuman, Morph, Cyborg.

Belt

Formally the Asteroid Belt — the fifth orbit, between the Mars and Jupiter orbits. A chaotic area of many small communes. The main industry is mining.

Carbonaceous Asteroid

Asteroids rich in carbon, organic compounds, and often water ice. Appear dark due to low Albedo. Valuable for life-support materials and feedstocks in organic chemistry. Often have a loose rubble-pile structure with deep Regolith, making them fragile and prone to dust hazards during mining. These substances are especially rare on Luna, keeping the price of carbonaceous substances high in the inner system; lifting them out of Earth's gravity well is faster mut costs more than Accelerating them form the Belt.

Colony

This term applies to all off-Earth communities, even those who are established independent nations. Colonization projects or recent colonies are used to mean more recent settlements, still dependent on a sponsor.

Cryotectonic

The movement of glacial ice, especially relevant on Europa. Many celestial bodies are largely or partially made of ice, so knowledge of how glaciers move is a matter of survival.

Degrav

The cumulative physiological harm from long-term residence in insufficient gravity. Symptoms include bone density loss, muscle atrophy, cardiovascular weakening, and balance impairment. In Microgravity, noticeable symptoms appear within days and become serious in weeks; in low gravity, effects develop over weeks to months. Commuting to higher gravity is a common prevention — many Spacers work in microgravity and live in Earth Standard Gravity habitats. Exercise slows Degrav, but recovery requires living in 0.8–1.2 Standard Gravity for extended periods, called Regrav.

Degrav and Regrav are terms invented for the Icarus Fall setting.

Delta-V

The measure of how much you can change your velocity with the Reaction Mass you have available. The basic currency of space travel. A ship with plenty of Delta-V can pick its fights and ports; one running low is at the mercy of local traffic and tides. In technical chapters it may be written as Δv; in cultural chapters it is usually spelled out as "delta-v." Compare Acceleration.

Deuterium

Hydrogen isotope with one proton and one neutron. Valuable for fusion reactors, naturally found in trace amounts in water and ice. Very little is consumed in Fusion Power, making supplies abundant and cheap.

Drop Lane

A designated shaft or cleared volume in a rotating habitat used for controlled descent along the gravity gradient. Every drop lane includes a fixed line or rail for rappelling and braking; some also provide secondary guide lines or rigid standoffs to limit drift. Lanes are kept free of obstacles and are usually lit or beaconed, with safety nets or arrest pads at the base. Descending a drop line is dangerous in the steep gravity gradient of a small habitat, paragliding down them is a popular hobby in large habitats.

Earth Standard Gravity

1 g, the acceleration due to Gravity at Earth’s surface: 9.80665 m/s². Used as a benchmark for habitat spin rate, acceleration in space, and human health limits. Gravities between 0.8 g and 1.2 g are considered healthy for long-term residence.

The health range is specific to the Icarus Fall setting, we don't know the actual range.

Earthborn

A human born and raised on Earth. Seen as chauvinistic and lazy by Spacers. Derogatory variants include dirtboy, mudman, from down the well, gravbound, and many more.

Environmental Specializations

Skills and adaptations for survival and maneuvering across the four most common environments of the Solar System. These are used both for training and as categories of genetic or mechanical modification.

Microgravity Environments of near-weightlessness, such as spacecraft in freefall. Focuses on orientation, translation, tool use, and stability. Days of exposure causes Degrav.

Low Gravity Environments between 0.15 g and 0.35 g, including many moons and small planets. Emphasizes balance, momentum control, and assisted locomotion. Distinct from Microgravity. Weeks of exposure risks Degrav.

Earth Standard Gravity Environments between 0.8 g and 1.2 g, considered healthy for long-term residence. Covers most Artificial Gravity habitats and the surface of Earth and Venus. Focus is endurance, load-bearing, and efficient movement.

Aquatic Submersion in water or other liquids. Includes maneuvering by swimming or with specialized equipment. Environments range from shallow lakes on habitats to high-pressure oceans.

Fusion Power

Energy generated by fusing light atomic nuclei, typically hydrogen isotopes, under extreme temperature and pressure. Powers Fusion Rockets, Ion Drives, and Habitats.

Fusion Rocket

A spacecraft propulsion system using controlled fusion reactions to heat and expel Reaction Mass. Offers high thrust but low Delta-V for long-range operations. Colloquially applied to chemical rockets as well. Compare Ion Drive.

Golden Age

The period from 2102 to 2310. Rapid technological and colonial expansion, ending in Icarus Fall. Characterized by large-scale infrastructure projects, high living standards, and Earth prestige dominating the Solar System.

Gravity

In technical terms, the force of attraction between masses, with strength determined by the gravitational constant G and the masses involved.

In everyday usage, “gravity” means the apparent gravity a person feels as weight, measured in Earth-standard units of g.

Apparent gravity can come from:

• Natural Surface Gravity on a planetary body
• Acceleration from thrust
• Spin Gravity in a rotating habitat

In science, g is lowercase; informal speech often uses a capital “G” (e.g., “one-point-two Gs”). Always written with a lowercase g when referring to acceleration relative to Earth gravity (e.g., 0.5 g, 2 g, –3 g). Do not capitalize except at the start of a sentence. In-character dialogue may use the spoken form “pulling Gs,” but all written rules and encyclopedia text use lowercase.

Groundbound

Adjusted to low-gravity living and unable to live at Earth gravity without extensive gravity therapy. Most colonized celestial bodies have low gravity and constant therapy is required to avoid becoming groundbound. Unlike Degrav from Microgravity, low-gravity living is sustainable over an entirelifetime. Luna, Mars, and Callisto has a ground-bound lower class living in conditions similar to serfdom. See Degrav, Regrav.

Defined for Icarus Fall, we don't know the exact risks of low-gravity living.

Habitat

Also called spin habitat, space habitat, cylinder habitat, or rotating habitat. A large, spinning station that generates Artificial Gravity through rotation. Ubiquitous for long-term living both in space and on low-gravity planets and moons.

Hydrogen Fuel

Common propellant for Fusion Rockets. Usually means protium stored as cryogenic liquid or bound in water ice. Can also refer casually to Deuterium or Tritium for fusion. Abundant all over the Solar System from Luna and outwards.

Icarus Fall

Also called the Fall or simply “Fall” in expressions like “Post Fall.” The catastrophic collapse of the Solar Alchemy Project in 2310, which destabilized the Sun and destroyed much of the inner Solar System's infrastructure. Marks the end of the Golden Age and the beginning of the hard-scrabble post-Fall present.

In-setting usage treats Icarus Fall as a proper name without the article “the,” while the Fall is a descriptive form that does take it.

Ion Drive

A highly efficient electric propulsion system that accelerates ions using electromagnetic fields. Characterized by low Acceleration and high Delta-V. Provides low thrust but extremely high specific impulse, ideal for constant low acceleration during long-duration travel. Compare Fusion Rocket.

Kessler Syndrome

A chain reaction of orbital debris collisions, creating clouds of high-velocity fragments that make certain orbits hazardous or impassable. The Fall destroyed much orbital infrastructure on Earth, much of this has been cleared or burnt up, but it still blocks some orbits.

Microgravity

An environment where gravity is extremely weak — near weightlessness — commonly on a spacecraft in freefall. Prolonged exposure leads to Degrav unless mitigated by Artificial Gravity.

Orbital Zone

A legal and navigational term. Each planet and the Asteroid Belt is considered its own orbital zone.

Precession

A gradual change in the orientation of a rotating body’s axis. In space this usually results from external torques — gravity gradients, sunlight pressure, or magnetic fields. Precession causes a slow “wobble” that alters pointing over time. Habitats compensate for precession with thrusters or magnetic torquers, but most still drift slightly, requiring updates to navigation and orientation markers. Compare Slew.

Radiation Shield

Any mass placed between crew and harmful radiation. In space, this usually means tanks of water, layers of Regolith, or waste slag wrapped around living areas. Small spacecraft shields are lighter and less effective, making storm shelters necessary during solar events.

Reaction Mass

Propellant expelled from a Small Craft’s engines to produce thrust. Can be hydrogen plasma, water, or even mined rock, depending on the drive.

Regolith

The loose surface material on an airless body — dust, gravel, and broken rock. has not been eroded, so particles are sharp. Gets everywhere, wears down tools, and can form dangerous clouds in microgravity.

Regrav

The period of readaptation to higher Gravity after Degrav. Recovery time depends on severity, health, and the difference between environments. Can take weeks in serious cases. Many habitats have Regrav wards where gravity can be adjusted by moving closer or farther from the spin axis.

Degrav and Regrav are terms invented for the Icarus Fall setting.

Remote

A location reachable only after long travel or during narrow windows, due to eccentric orbits, high inclination, or hazards. Remoteness changes over time — debris fields from Kessler Syndrome can make a place remote until they clear.

This usage is specific to the Icarus Fall setting.

Slew

A deliberate change in the orientation of a spacecraft or habitat. Slewing is done to point docks, sensors, or radiators in a new direction. The term refers only to attitude, not to changing orbit or position. Compare [#Precession|Precession]].

Small Craft

Often called simply “craft,” these are spacecraft unsuited for interplanetary travel or long missions. Usually Fusion Powered with Fusion Rockets with endurance in hours. Need to seek shelter during severe solar storms.

Broad categories:

• Shuttles — Primarily for transport, rated by cargo/passenger load.
• Fighters — Combat craft, subdivided into:

• Interceptors — Very high Acceleration, low Delta-V
• Attackers — Balanced Acceleration and Delta-V
• Boarders — Extreme Acceleration, low Delta-V

Solar Alchemy

The vast Golden Age project of the 22nd and 23rd centuries called Dedalus Rise that attempted to manipulate solar fusion output for energy production and stellar engineering. Its failure caused the Icarus Fall.

Solar System

The Sun and all gravitationally bound bodies — planets, moons, asteroids, comets, and artificial satellites. Often split into “inner” and “outer” system, with the Belt sometimes counted as part of either or as its own region.

Solar Wind

A constant stream of charged particles from the Sun. Can cause electrostatic charging, erode surfaces, and sometimes produce detectable X-ray emissions. After the Fall, activity increased dramatically, making radio and radar unreliable across much of the Solar System and rendering solar power and sails impractical.

Spaceship

Sometimes just “ship” or “capital ship.” A spacecraft capable of interplanetary travel, usually powered by an Ion Drive. Like Habitats, they have Artificial Gravity and a Radiation Shield. Endurance in weeks or months.

Spacer

A person living off Earth, usually in a Space Habitat. Increasingly means someone born and raised away from Earth. Derogatory variants include flipper, skinny, flyweight, and drifter. Compare Earthborn.

Spin Gravity

Artificial gravity generated by rotation. Too fast a spin causes vertigo and steep gravity gradients. In Habitats, gravity increases farther from the axis; in Ships, spin is often combined with the low acceleration from Ion Drives.

Surface Gravity

The Gravity at the surface of a body. Only Earth and Venus have gravity conducive to human long-term health.

Tritium

Radioactive hydrogen isotope with one proton and two neutrons. Extremely rare naturally; produced in reactors. Used in advanced Fusion fuel cycles, mostly for military applications.