MECO is also an acronym for
Main Engine Cut-Off, which is a crucial point during a
Space Shuttle launch. It signifies the point at which the
main engines on the
orbiter stop thrusting; at this point, the Shuttle has enough velocity to reach the planned
orbit either directly (called
direct insertion - ooo!) or using the
OMS thrusters alone.
Immediately after MECO, the External Tank is jettisoned and begins its fall back into the atmosphere. MECO typically occurs at around 68 or 69 miles of altitude.