Abort to Orbit - STS-51F Mission - Challenger

On July 29, 1985, space shuttle Challenger lifted off on mission STS-51F. 5 1/2 minutes after launch, the center main engine went down forcing the shuttle to perform the only ascent launch abort in program history with an Abort-To-Orbit. The two remaining engines fired for an extra minute to place Challenger in a lower orbit than planned but safe. The Spacelab 2 mission went on mostly as planned with 85% of the science objectives met. An abort to orbit (ATO) was available when the intended orbit could not be reached but a lower stable orbit was possible. The Mission Control Center in Houston, Texas (located at Lyndon B. Johnson Space Center), observed an SSME failure and called "Challenger-Houston, abort ATO". The moment at which an ATO became possible was referred to as the "press to ATO" moment. In an ATO situation, the spacecraft commander rotated the cockpit abort mode switch to the ATO position and depressed the abort push button. This initiated the flight control software routines which handled the abort. In the event of a loss of communications, the spacecraft commander could have made the abort decision and taken action independently.