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.

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 (C-type 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. Especially rare on Luna, keeping the price of carbonaceous substances high in the inner system.

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 fuel or Reaction Mass you have. 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. 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.

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.

Earthborn

A human born and raised on Earth. Seen as chauvinistic and uncouth by Spacers.

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 and high Delta-V for long-range operations. See main entry.

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”).

Habitat

Also called space habitat, cylinder habitat, or rotating habitat. A large, spinning station that generates Artificial Gravity through rotation. Common as long-term living space. See main entry.

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 in the outer Solar System.

Icarus Fall

Also called the Fall or simply “Fall.” The catastrophic collapse of the Solar Alchemy Project in 2310, which destabilised the Sun and destroyed much of the inner system’s infrastructure. Marks the end of the Golden Age and the beginning of the hard-scrabble present.

Ion Drive

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

Kessler Syndrome

A chain reaction of orbital debris collisions, creating clouds of high-velocity fragments that make certain orbits hazardous or impassable. After the Fall, this still blocks some Earth orbits.

Microgravity

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

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 spacecraft’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. Lacks erosion, 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.

Small Craft

Often called simply “craft,” these are spacecraft unsuited for interplanetary travel or long missions. Usually fusion-powered with endurance in hours.

Two 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, very low delta-v

Solar Alchemy

The vast Golden Age project 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.” 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.

Spacer

A person living off Earth, usually in a space habitat. Increasingly means someone born and raised away from Earth. See 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 partial thrust.

Surface Gravity

The gravity at the surface of a body. Only Earth and Venus have gravity suitable for long-term human 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.