Definitions list
Click one of the letters above to advance the page to terms beginning with that letter.
  • aborted
    Describes an operation interrupted prematurely due to a failure. For example, an aborted launch.
  • acceptance test
    Test designed to verify that a product complies with specifications.
  • aerocapture
    Use of friction against a planet’s atmosphere to slow a spacecraft for insertion into orbit.
  • aeronomy
    Study of the upper reaches of the atmosphere of Earth or other planets.
  • aerospace
    Relating to aeronautics and space.
  • aircraft / aeroplane
    Heavier-than-air flying machine kept in the air by reaction of the atmosphere, without the reaction of the ground.
  • airlock
    Compartment that seals off a habitable part of a spacecraft from space. Astronauts go through an airlock when performing an extravehicular activity.
  • airship
    Lighter-than-air craft capable of obtaining lift in a gaseous atmosphere without engine propulsion.
  • albedo
    From the Latin word albedo, meaning “whiteness”. The albedo is the fraction of light reflected or scattered by a body. Its value is between 0 and 1.
  • altimetry
    Technique for measuring height using a radar beam, for example to map the topography of the ocean surface. Altimetry also yields information about the Earth’s geoid, ocean circulation, wave heights, sea state and wind speed.
    How altimetry works
  • alunir
    Se poser sur la Lune. Terme à proscrire. Utiliser atterrir
  • anechoic chamber
    Closed chamber whose walls are lined with an absorbent material that does not reflect electromagnetic or acoustic waves. Used to simulate the vacuum of space.
  • anisotropy
    Property of being directionnally dependant. The properties of an anisotropic object will differ according to the direction of measurement.
  • apesanteur
    Synonyme d’impesanteur. Ce mot est déconseillé en raison des risques de confusion pour l’oreille entre « la pesanteur » et « l’apesanteur ».
    Qu'est-ce que l'impesanteur ?
  • apoapsis
    Point on a satellite’s orbit farthest from the body about which it is orbiting. Specific terms are used for individual bodies, for example, apogee (Earth), apolune (Moon), apojove (Jupiter) and aphelion (Sun).
  • apogee
    Point on an Earth-orbiting satellite’s orbit farthest from Earth.
  • apogee kick motor
    Rocket engine on board a satellite used near apogee to impart the thrust required to obtain a circular orbit, or, more generally, to raise its altitude at perigee, in which case the target altitude is the apogee. This type of thruster is used, for example, to boost a man-made satellite into geostationary orbit.
    How orbital manoeuvres work
  • arrimage
    Fixation d’une charge utile à l’intérieur ou à l’extérieur d’un vaisseau spatial. Terme à proscrire, utiliser amarrage.
  • artificial satellite / man-made satellite
    Object built on Earth and designed to orbit around a celestial body. Since 1957, more than 4,000 man-made satellites have been launched into orbit around the Earth, as well as the Sun, Moon, Mars and Venus. The vast majority of artificial satellites (95%) are unmanned.
    How satellites work
  • asteroid
    Small planet in the Solar System, varying in size from 1,000 kilometres to a fraction of a kilometre. There are thought to be at least 1 million asteroids more than one kilometre across. Most are between the orbits of Mars and Jupiter.
  • astrometry
    Branch of astronomy dealing with the position and motions of celestial objects.
  • astronaut
    Occupant of a spacecraft (U.S., Europe).
  • astronautics
    Science of travel in space. From the French astronautique, a term coined by Joseph-Henri Rosny in 1927.
  • astronomical unit (AU)
    Unit of distance equal to the radius of Earth’s orbit around the Sun, that is, 149,597,870 km. Used to express distances in the Solar System.
  • astronomy
    Science that studies the positions, motions and structure of celestial objects (stars, planets, galaxies, natural satellites, etc.)
  • astrophysique
    Branche de l’astronomie qui étudie la physique et l’évolution des diverses composants de l’Univers.
  • atmosphere
    Gaseous envelope shrouding certain planets in the Solar System. Earth’s atmosphere is the barrier that separates us from space.
  • attitude
    Position of a spacecraft with respect to three reference axes. Synonym: orientation.
  • avionics
    Electronic and computer equipment used to fly an aircraft or spacecraft.
  • aérosols
    L’atmosphère se compose de molécules de gaz et de petites particules solides et liquides en suspension dans l’air, appelées aérosols. Certains aérosols sont naturellement produits par les volcans, les embruns (océans), le sable, ou l’érosion de surface provoquée par le vent. D’autres aérosols résultent de l’activité humaine, comme la poussière issue des activités agricoles, la fumée résultant de la combustion de la biomasse et des énergies fossiles, du brouillard induit de manière photochimique par les pollutions de véhicules. Les gouttes et cristaux de glace résultant de la condensation de l’eau sont aussi des aérosols.