Definitions list
Click one of the letters above to advance the page to terms beginning with that letter.
  • observatory
    Structure specially designed for astronomy observations.
  • onde gravitationnelle
    Oscillation de la courbure de l'espace-temps prédites par la théorie de la Relativité générale. À la différence des ondes électromagnétiques, les ondes gravitationnelles interagissent très peu avec la matière. L’univers est pour ainsi dire transparent aux ondes gravitationnelles. Elles n'ont encore jamais été observées directement et constituent une nouvelle fenêtre d’observation potentiellement exceptionnelle pour étudier l'univers et son évolution.
  • orbit
    Trajectory described by a man-made or natural satellite around a celestial body. It corresponds to the sequence of positions of the satellite in space.
    What is an orbit?
  • orbit
    1. To describe an orbit. Synonym: gravitate.

    2. To place a spacecraft into orbit around a celestial body.
  • orbit determination / orbitography
    Technique that consists of determining and representing a satellite’s orbit.
  • orbit slot
    Region in space within which a geostationary satellite must remain to fulfil its mission without interfering with neighbouring satellites.
  • orbital debris
    Solid waste of man-made origin orbiting Earth. Some 8,000 debris objects larger than 10 centimetres have been catalogued, 20% of which are spent satellites. There are billions of microscopic debris objects.
  • orbital elements / orbital parameters
    Set of numeric values defining an orbit described by an object in space, and its position on that orbit.
    What is an orbit?
  • orbital inclination
    Angle between the orbital plane of a man-made satellite and the equatorial plane.
    What is an orbit?
  • orbital mechanics
    Branch of astronautics that studies the motions of man-made satellites and determines their orbits.
  • orbite d'attente
    Temporary orbit, usually near a planet, from which a spacecraft can be moved to a new orbit at an appropriate time.
    What is an orbit?
  • orbiter
    Spacecraft designed to remain in orbit around a celestial body to perform a remote-sensing mission.
  • orbiting
    Operation intended to place a spacecraft into orbit around a celestial body as a man-made satellite.
  • orthostatic
    Related to the standing position. For humans, the head is therefore above the heart in the orthostatic position. Antonym: anti-orthostatic.
  • oxidizer
    Oxidizing substance that, when combined with a reducer (fuel), causes combustion to generate thrust for a rocket engine.
  • ozone
    L’Ozone est l’un des nombreux gaz présents dans l’atmosphère en petite quantité. C’est une molécule qui contient trois atomes d’oxygène (O3).