Definitions list
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  • heat shield
    Device designed to protect part of a spacecraft from heating, particularly when entering a gaseous atmosphere at high speed. It is made of insulating or ablative material.
  • Heliocentric (Sun-centred) theory
    Theory that places the Sun at the centre of the “world”. It was originally expounded by the Greeks in the 3rd century and taken up later by Copernicus in the 16th century, after which it slowly gained acceptance.
  • highly inclined orbit
    Orbit inclined more than 45° to the equatorial plane.
    What is an orbit?
  • hydrazine
    Colourless, toxic and corrosive liquid with physical properties similar to water. Certain hydrazine compounds are used as fuel.
  • hydrosphere
    Layer of water at or near the Earth's surface that includes all liquid and frozen surface waters.
  • hypergravity
    Gravity greater than that experienced on Earth.
  • hyperpesanteur
    Pesanteur supérieure à celle de la Terre.