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thumb|396px|link=Atmospheric Drag was the process of prolonged reduction in the altitude of a satellite's orbit and resulting in it sinking into the Earth's atmosphere. This could be achieved naturally through orbital decay or synthetically through reducing it's orbit to reduce space junk. 

Numerous stations in Gravity suffered from this as a result of the debris strike. 

CausesEdit

This could be due to drag produced by an atmosphere due to frequent collisions between the satellite and surrounding air molecules. The drag experienced by the object was larger in the case of increased solar activity because it heated and expanded the upper atmosphere. For larger bodies, tidal effects could cause orbital decay and for even larger ones gravitational radiation could have an effect.

A major cause of orbital decay for satellites in low Earth orbit was the drag of Earth’s atmosphere. During solar maxima, the Earth's atmosphere caused significant drag up to a hundred kilometers higher than during solar minima.

Atmospheric drag resulting in satellite re-entry could be described by the following sequence:

  • lower altitude → denser atmosphere → increased drag → increased heat → usually burns on re-entry
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The Tiangong explodes.

Orbital decay involved a positive feedback effect where the more that the orbit decayed, the lower that it's altitude dropped and the lower the altitude, the faster the decay. Decay was also particularly sensitive to external factors of the space environment such as solar activity which are not very predictable.

Atmospheric drag exerted a significant effect at the altitudes of space stations, space shuttles and other manned Earth-orbit spacecraft and satellites with relatively high "low Earth orbits" such as the Hubble Space Telescope. Space stations typically required a regular altitude boost to counteract orbital decay (See also orbital station-keeping). Uncontrolled orbital decay brought the Skylab space station down and (Relatively) controlled orbital decay was used to de-orbit the Mir space station. Orbital boosts for the International Space Station (ISS) are regularly needed and are one limiting factor for the length of time that the ISS could go between visits from transit spacecraft.

Regular orbital boosts are also needed by the Hubble Space Telescope, though on a longer time scale, due to it's much higher altitude. However, orbital decay was also a limiting factor to the length of time that the Hubble could go without a maintenance rendezvous, the most recent performed successfully by STS-125 with the space shuttle, Atlantis launching on May 11, 2009.

Victims in GravityEdit

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