Reentry is the term used to refer to the transition from the
vacuum of
space to the
atmosphere of a
planet or other celestial body. This often occurs at high speed to take advantage of
aerobraking (using wind resistance to slow the vehicle) and is a critical time for the
spacecraft. Any errors in this portion of the flight profile are difficult to recover from and will probably have large impact upon the mission. Death and/or mission failures have occurred in this flight regime.
See also: Space Shuttle Columbia disaster