Atmospheric entry is the movement of human-made or natural objects as they enter the atmosphere of a celestial body from outer space—in the case of Earth from an altitude above the Kármán Line, (100 km). This article primarily addresses the process of controlled reentry of vehicles which are intended to reach the planetary surface intact, but the topic also includes uncontrolled (or minimally controlled) cases, such as the intentionally or circumstantially occurring, destructive deorbiting of satellites and the falling back to the planet of "space junk" due to orbital decay.
Most objects entering the atmosphere are not released from rest just above it, but rather are entering at hypersonic speeds because they are on suborbital (e.g. ICBM reentry vehicles), orbital (e.g. the Space Shuttle), or unbounded (e.g. meteors) trajectories. Therefore, controlled atmospheric entry often requires special methods to protect against severe aerodynamic heating. Various advanced technologies have been developed to enable atmospheric reentry and flight at extreme velocities.
Read more about Atmospheric Entry: History, Terminology, Definitions and Jargon, Blunt Body Entry Vehicles, Shock Layer Gas Physics, Thermal Protection Systems, Feathered Reentry, Inflatable Heat Shield Reentry, Entry Vehicle Design Considerations, Notable Atmospheric Entry Accidents, Uncontrolled and Unprotected Reentries, Successful Atmospheric Re-entries From Orbital Velocities, Selected Atmospheric Re-entries, Further Reading
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