An ATO is an abort mode
used to boost the orbiter to a safe orbital altitude when performance
has been lost and it is impossible to reach the planned orbital
altitude. If a Space Shuttle main engine fails in a region that
results in a main engine cutoff under speed, the Mission Control
Center will determine that an abort mode is necessary and will
inform the crew. The orbital maneuvering system engines would
be used to place the orbiter in a circular orbit.