Glossary of Space Exploration Terminology

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G
g
The symbol for the acceleration of a freely moving body due to gravity at the surface of the Earth. Alternatively, 1 g.
g-Force
A force caused by acceleration expressed in g's.
Galaxy
A very large system of stars, gas and dust isolated from its neighbors by an immensity of space; an "island universe".
GALCIT
Guggenheim Aeronautical Laboratory of the California Institute of Technology.
Gamma rays
Very short, highly-penetrative electromagnetic radiation with a shorter wavelength than X-rays; produced in general by emission from atomic nuclei.
Gas generator
A chamber in which propellant is burned to produce high pressure gas that is then used to drive a turbine, e.g. turbopump.
Gas giant
A large planet composed mostly of gas, e.g. the Jovian planets.
GATV
Gemini-Agena Target Vehicle.
Gauss
CGS unit of magnetic induction (after the German mathematician Karl F. Gauss).
GE
General Electric Company of the USA.
GEO
Geostationary Orbit. Also abbreviated GO.
Geo-
Prefix referring to the Earth.
Geocentric
Earth centered.
Geodesy
The science of the Earth's shape.
Geomagnetic storm
A worldwide disturbance of the Earth's magnetic field, distinct from regular diurnal variations.
Geospace
Also called the solar-terrestrial environment, geospace is the domain of Sun-Earth interactions. It consists of the particles, fields, and radiation environment from the Sun to Earth's space plasma environment and upper atmosphere. Geospace is considered to be the fourth physical geosphere (after solid earth, oceans, and atmosphere).
Geostationary orbit
A geosynchronous orbit with an inclination of zero degrees. A spacecraft in such an orbit appears to remain fixed above a particular point on the equator.
Geostationary transfer orbit
An elliptical orbit used to transfer a space vehicle from low earth orbit to geostationary orbit.
Geosynchronous orbit
A prograde, circular, low inclination orbit about Earth having a period of 23 hours 56 hours 4 seconds. A spacecraft in such an orbit appears to remain above Earth at a constant longitude, although it may seem to wander north and south.
GH2
Gaseous Hydrogen.
GHz
Gigahertz, equal to one billion hertz.
Gimbal
A mechanical frame for a gyroscope or power unit, usually with two perpendicular axes of rotation.
GMT
Greenwich Mean Time.
GN&C
Guidance, Navigation and Control.
GO
Geostationary Orbit. Also abbreviated GEO.
GOX
Gaseous Oxygen.
Grain
The rubberlike mass of chemical propellant that provides propulsion in solid fuel rockets. The shape of the grain determines the rate and pattern of burn and thus controls thrust.
Gravitational waves
Einsteinian distortions of the space-time medium predicted by general relativity theory (not yet detected as of November 1995).
Gravity
The force responsible for the mutual attraction of separate masses.
Gravity assist trajectory
A trajectory in which angular momentum is transferred from an orbiting planet to a spacecraft approaching from behind. The result is an increase in the spacecraft's velocity.
Gravity field survey
The mapping of a planet's mass distribution by studying variations in the in the planet's gravity field strength made evident by minute Doppler shifts in an orbiting spacecraft's radio signal.
Gravity waves
Certain atmospheric waves within a planet's atmosphere.
Great circle
An imaginary circle on the surface of a sphere whose center is at the center of the sphere.
Greenwich mean time
See universal time.
GSFC
Goddard Space Flight Center (Greenbelt, Maryland).
GSO
Geosynchronous Orbit.
GTO
Geostationary Transfer Orbit.
Guillotine
A device equipped with explosive blades used to cut cables, water lines, wires, etc. during separation of spacecraft modules.
Gyration
The circular motion of ions and electrons around magnetic field lines.
Gyroscope
A spinning, wheel-like device that resists any force that tries to tilt its axis. Gyroscopes are used for stabilizing the attitude of rockets and spacecraft in motion.

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Rocketry & Space Technology

Glossary courtesy of Robert Braeunig's
Rocketry & Space Technology website.