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 most Belt hauls. Often causally termed speed. Compare Delta-V, Standard Earth 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 slower or barely at all, and can be spotted more easily.

Artificial Gravity

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

Belt

Formally the Asteroid Belt, this is the fifth orbit, between Mars and Jupiter. 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. Typically classified as C-type. 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. This keeps 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 there are noticeable symptoms after a days, serious in weeks. In low gravity this changes to weeks and months, slower in higher gravity. Commuting to higher gravity is a common way to prevent Degrav, many Spacers work in Microgravity and live in Earth Standard Gravity habitats.. Health regiments slows degrav, but recovery requires living in conditions of 0.8 to 1.2 Standard Gravity for extended periods, this is 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 its ports; one running low is at the mercy of local traffic and tides. Compare Acceleration, Reaction Mass.

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 available 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 in the range from 0.8 g to 1.2 g are considered healthy for long-time residence.

This term is real but the health range is for the Icarus Fall setting.

Earthborn

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

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, gravity is the force of attraction between masses, with its strength determined by the gravitational constant G (a fixed value) and the masses involved. In day-to-day usage, “gravity” means the apparent gravity a person feels as weight, measured in Earth-standard units of g (~9.81 m/s²).

Apparent gravity can come from three sources: natural surface gravity on a planetary body; acceleration from thrust; or centrifugal force in a rotating habitat. In specifications and scientific notation, g is lowercase. In speech and informal writing, Belters often use a capital “G” (e.g., “the deck’s at one-point-two Gs”). See Acceleration, Artificial Gravity, Standard Earth Gravity.

Habitat

Also called space habitat, cylinder habitat, or rotating habitat. A large, spinning station in space that generates artificial gravity through rotation. Common long-term living environment. See main entry.

Hydrogen Fuel

Common propellant for Fusion Rockets. In Spacer terms, usually refers to ordinary hydrogen (protium) stored as cryogenic liquid or more commonly bound in water ice. In casual language this can refer to Deuterium or Tritium, feedstock for Fusion Power. Abundant in the outer Solar System.

Icarus Fall

Also called the Fall or simply Fall as in the expressions post-Fall and pre-Fall. The catastrophic collapse of the Solar Alchemy Project in 2310, which destabilized the Sun and destroyed much of the inner system’s infrastructure. Marks the end of the Golden Age and the beginning of the fragmented, 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 such as between planetary orbits. Characterized by low Acceleration and high Delta-V. See main entry.

Kessler Syndrome

A chain reaction of orbital debris collisions, creating clouds of high-velocity fragments that make certain orbits hazardous or impassable. Great problem on Earth after Icarus 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 effects on human health unless mitigated by Artificial Gravity.

This term is scientific, but the related term Degrav is developed for the Icarus Fall setting.

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 the living areas. Small spacecraft shields are lighter and less effective, making storm shelters necessary during solar events. Spaceships built for long-term travel need good shielding.

Reaction Mass

Propellant expelled from a spacecraft’s engines to produce thrust, as in Newton’s third law. Can be anything from hydrogen plasma to water or even mined rock, depending on the drive type.

Regolith

The loose surface material on an airless asteroid, moon, or planet — dust, gravel, and broken rock. Can range from soft powder to boulder fields. A lack of wind and water means regolith has not eroded and remains sharp and pointy. Regolith is a hazard; it gets everywhere, wears down tools, and can drift into dangerous clouds in microgravity.

Regrav

The period of readaptation to higher gravity after suffering Degrav from extended time in low gravity. Recovery time depends on the severity of the Degrav, overall health, and the gravity difference between environments and can take weeks in serious cases. Most habitats have Regrav elevator wards where gravity can be adjusted by going up or down from the central axis for optimum treatment.

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

Remote

A “remote location” is reachable only after long travel or during limited windows, due to eccentric orbits, high inclination, or navigation hazards. Remoteness is time-dependent — debris fields like those from Kessler Syndrome can make a place remote until they clear. By this definition, Earth could qualify, but as the center of human life, it is never treated as such.

This usage is specific to the Icarus Fall setting.

Small Craft

Often called simply “craft,” this term covers all spacecraft unsuited for interplanetary travel or long-duration missions. Usually fusion-rocket powered, they are designed for short-range operations with endurance measured in hours.

Two broad categories exist:

• Shuttles — Primarily for transport and civilian use, rated by cargo or passenger load. Includes craft for exploration, mining, and exploration.
• Fighters — Combat-oriented, subdivided into:

• Interceptors — Very high acceleration, low delta-v.
• Attackers — Balanced between acceleration and delta-v.
• Boarders — Extreme acceleration, very low delta-v.

This usage is specific to the Icarus Fall setting.

Solar Alchemy

The vast Golden Age project that attempted to manipulate solar fusion output for energy production and stellar engineering. Called the Dedalus Project, which led to the name Icarus Fall for its failure in 2310 and the time since.

This term is invented for the Icarus Fall setting.

Solar System

The Sun and all objects gravitationally bound to it — planets, moons, asteroids, comets, and artificial satellites. Often divided in the "outer" system from the Belt and Inwards and "outer" from the Belt outwards. The Belt is sometimes considered part of either, sometimes considered to be its own part in between.

Solar Wind

A constant stream of charged particles from the Sun. It can cause electrostatic charging, erode exposed surfaces, and sometimes create detectable X-ray emissions from certain minerals. A hazard during storms, and a subtle tool for prospectors who know how to read it. After Icarus Fall, solar activity has increased manyfold, making radio and radar useless in most of the Solar System. This made solar power and solar sails too unreliable to use.

Spaceship

Sometimes just Ships. A spacecraft capable of interplanetary travel, usually powered by Ion Drive. Similar to habitats, these feature Artificial Gravity and a Radiation Shield. Endurance measured in weeks.

This term is invented for the Icarus Fall setting.

Spacer

Person living off Earth, usually in a Space Habitat. Increasingly this is starting to mean a human born and raised off Earth. See Earthborn.

Spin Gravity

Artificial gravity generated by rotation. Too fast a spin causes vertigo and sharp gravity gradients. Further from the central axis gravity increases, making lower levels in a habitat suffer progressively higher gravity. Spaceships use spin gravity, Ion Engines generate too weak thrust to have a significant effect.

This term is scientific, but had been developed for use in the Icarus Fall setting.

Surface Gravity

The strength of gravity at the surface of a body, usually less than Earth Standard Gravity. Only on Earth and Venus is Surface Gravity suitable for 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.