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Re-entry vehicle

A re-entry vehicle is a vehicle used in space missions to safely re-enter Earth's atmosphere. This usually requires much heat shielding, due to the high temperatures caused by friction with the air.

There are several basic structural approaches to building a reentry vehicle. The first developed and most commonly used is the ballistic capsule, a relatively simple cone-shaped vehicle with little maneuverability. By tilting the ballistic capsule some aerodynamic lift can be achieved, however, providing some cross-range capability. Examples of ballistic capsules include the reentry vehicles for Soyuz, Vostok, Apollo, Gemini, Mercury, Corona, and many others.

Another approach is the winged reentry vehicle that uses stubby wings for maneuvering during descent much like a conventional glider. This approach has been used by the American Space Shuttles and the Soviet Buran.

Finally, the lifting body approach has been proposed but so far has not been used by any actual reentry vehicles.

Unmanned spacecraft generally have no re-entry capabilities, and are usually left in orbit or allowed to burn up falling back to Earth. Exceptions include early spy satellites that had reentry vehicles for returning photographic film to Earth and sample-return missions from other celestial bodies (or from open space, as in the Stardust probe). Spacecraft that land on other celestial bodies use what are more properly termed "entry vehices", since they aren't re-entering an atmosphere they have previously departed. These include various Mars landers, various Venus probes, Galileo's Jupiter atmosphere probe, and Cassini's Huygens Titan probe. Lunar and asteroid landers do not require entry vehicles as these bodies lack atmospheres.

When a spacecraft's heat shielding is insufficient or damaged, the results can be catastrophic; the recent destruction of the Space Shuttle Columbia is an example of this.

ICBMs also use re-entry vehicles to deliver nuclear warheads from orbit intact to their targets.