Glossary of Space Exploration Terminology

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A
AACS
Attitude & Articulation Control Subsystem.
AAF
Association Astronautique Francaise.
AAS
American Astronautical Society.
ABL
Allegheny Ballistics Laboratory.
Ablation
The erosion of a solid body by a high-temperature gas stream moving with high velocity, e.g. a reentry vehicle's heat shield which melts or chars under the effects of air friction.
ABMA
Army Ballistic Missile Agency (USA).
Abort
To cancel or cut short a mission.
Absolute zero
The temperature at which all heat action ceases, -273.16oC (-459.69oF).
Acceleration
A change in velocity, including changes of direction and decreases as well as increases in speed.
Accelerometer
A device that senses changes in speed along its axis.
ACS
Attitude Control System.
Active heating
The use of resistive electric heaters or radioisotope heaters to keep spacecraft components above their minimum allowable temperatures.
Active sun
The Sun during times of frequent solar activity such as sunspots, flares, and associated phenomena.
Actuator
A device which transforms an electric signal into a measured motion using hydraulic, pneumatic or pyrotechnic (explosive) action.
Aerobraking
The process of decelerating by converting velocity into heat through friction with a planetary atmosphere.
Aerodynamic heating
The heating of a body due to the passage of air or other gases over the body; caused by friction and compression processes.
Aeronautics
The science of building and operating vehicles for flight.
Aerozine 50
A storable liquid fuel: 50% hydrazine, 50% UDMH.
AIAA
American Institute of Aeronautics and Astronautics (USA).
AIDAA
Associazione Italiana di Aeronautica e Astronautica.
Aileron
A hinged surface on the wing of an aircraft or spacecraft used to adjust the craft's angle of flight.
Aimpoint
The point in the planet's plane that spacecraft aim for to either fly by or enter orbit.
Air lock
A compartment separating areas a different environment, especially different air pressures, that is used for entry to and departure from a spacecraft.
Airglow
The visible light that appears at night in the upper atmosphere.
Albedo
Reflectivity; the ratio of reflected light to incident light. The fraction of the sunlight which is reflected off a planet.
Algae
A group of simple organisms, mostly aquatic, which contain chlorophyll and thus provide a means of photosynthesis. They could be used to absorb carbon dioxide and provide nourishment in a spaceship.
ALSEP
Apollo Lunar Surface Experiment Package.
Altimeter
A device that measures altitude above the surface of a planet or moon. Spacecraft altimeters work by timing the round trip of radio signals bounced off the surface.
Ambient
Environmental conditions, such as pressure or temperature.
Analog computer
A computing machine that works on the principle of measuring, as distinct from counting, in which the measurements obtained (as voltages, resistances, etc.) are translated into desired data.
Angle of attack
The angle between the velocity vector and the longitudinal axis of a missile or rocket.
Angstrom
A unit for the measurement of wavelength. Equals one hundred millionth of a centimeter (0.003937 millionth of an inch).
Annular
Pertaining to, or having the form of a ring.
Anomaly
The angular distance between the position of a planet and its last perihelion, or between that of a satellite and its last perigee.
Anti-matter
A hypothetical form of matter of which the atoms are composed of anti-particles, as protons, electrons, etc. assumed to carry charges opposite to those associated with ordinary matter. Particles having such properties have been produced in particle accelerators.
Antipodal
Pertaining to, or located on, the opposite side of the Earth.
AOCS
Attitude & Orbit Control System.
Aperture
The diameter of an opening; the diameter of the primary lens or mirror of a telescope.
Apex
The point towards which a body is moving.
Aphelion
That point in a solar orbit which is farthest from the Sun.
Apoapsis
That point in an orbit which is farthest from the primary.
Apogee
That point in a terrestrial orbit which is farthest from the Earth.
Apolune
That point in a lunar orbit which is farthest from the Moon.
Argument
Angular distance.
Argument of periapsis
In an orbit, the angular distance between the point of periapsis and the ascending node.
Arianespace
A private limited company established for the purpose of producing, financing and marketing the ESA Ariane launch vehicle. Comprises European companies concerned in the rocket's development, CNES and several banks. US agent is Grumman Aerospace.
ARS
American Rocket Society (USA).
Artificial gravity
Use of centrifugal force to simulate weight reaction in a condition of free-fall. May be achieved by spinning the vehicle to make the centrifugal force of the outer periphery or bodies within the vehicle to replace the weight reaction experienced at Earth's surface.
ASAT
Anti-satellite.
Ascending node
The point at which an orbiting object or spacecraft, traveling from south to north, crosses the plane of the equator.
Ascent module
That part of a spacecraft that ascends from the surface of a planet or moon to rendezvous and dock with an orbiting spacecraft.
Asteroid
A small, usually irregularly shaped body orbiting the sun, most often at least partially between the orbits of Mars and Jupiter.
Asteroid belt
A 1/2 AU wide region between the orbits of Mars and Jupiter where most asteroids are found.
Astronaut
A person who flies in space, whether as a crew member or passenger.
Astronautics
The science and technology of space flight.
Astronomical unit
The mean distance of Earth from the Sun, i.e. 92,955,807 miles (149,597,870 km).
Astrophysics
Study of the physical and chemical nature of celestial bodies and their environs.
ATDA
Agena Target Docking Adapter.
Atmospheric balloon
An instrumented package suspended from a buoyant gas bag; deployed in a planet's atmosphere to study wind circulation patterns.
Atmospheric pressure
The weight of air on surfaces within Earth's atmosphere, about 14.7 psi (101 kPa) at sea level. Such pressure is also supplied artificially in spacecraft and spacesuits.
Atmospheric probe
A small instrumented craft which separates from the main spacecraft prior to closest approach to a planet to study the gaseous atmosphere of the body as it drops through it.
Attenuation
The decrease of a propagating physical quantity, such as a radio signal, with increasing distance from the source, or from some obstruction.
Attitude
Orientation of a space vehicle as determined by the relationship between its axes and some reference plane, e.g. the horizon.
Attitude & articulation control subsystem
The onboard computer that manages the tasks involved in spacecraft stabilization via its interface equipment. For attitude reference, star trackers, star scanners, solar trackers, sun sensors, and planetary limb trackers are used.
Attitude control
The system that turns and maintains a spacecraft in the required direction as indicated by its sensors.
AU
Astronomical Unit.
Aurora
Arcs, rays or swaying curtains of green, yellow or white lights seen in latitudes of about 70o, such as Aurora Borealis or Northern Lights, and Aurora Australis or Southern Lights; caused by streams of electrified particles, emitted by the Sun, trapped in the Earth's magnetic field.
Autopilot
A system or device that controls a vehicle's flight at a preset course and altitude.
Azimuth
The angular position of an object measured in the observer's horizontal plane, usually from north through east. Bearing or direction in the horizontal plane. As one of the coordinates expressing celestial location, it is sometimes used in tracking spacecraft.

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Rocketry & Space Technology

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