In 2005, during the first launch after the Space shuttle Columbia disaster, a shuttle was threatened by another flying menace: a vulture that smacked into the external tank during takeoff.

Discovery's final flight follows several delays due to technical problems and repairs to its external fuel tank, but NASA's mission launch director Mike Leinbach says the shuttle is still space-ready.

A major exception, the space shuttle orbiter, USES three onboard liquid-fuel main engines supplied by a disposable external tank and a pair of solid-fuel boosters to reach space.