Did the Apollo command module have an abort mode?

Question

Many manned space exploration vehicles have some way to abort, to end the mission as quickly as possible and get back to relative safety.

I'm wondering if the Apollo command module had an abort, a way to get back to Earth while enroute to the Moon.

If so, why wasn't it used on Apollo 13?

Answer 1

According to a Wikipedia article Apollo missions had multiple abort modes:

• Pad abort - If an emergency occurred during the last few minutes before launch, the launch escape system could pull the command module away from the rocket stack.
• Mode I - Would have been used during Stage I burn and would have used the lauch escape system to pull the command module out of the way. It was subdivided into IA, IB, and IC, depending on altitude: Below 3000 meters, IA would have been used. In it the command module would be moved out of the flight path of the rocket stack and pulled away by the launch escape system. IB would have been used between 3000 meters and 30.5 km. In it, canards would be used to turn the command module into a "bottom forward" flight so that the parachutes could deploy properly. IC was similar to IB, but would use motors to orient the CM. When the rocket/spacecraft stack was too high for the launch escape system to be useful, that system was jettisoned.
• Mode II - In the event of a problem early in the second stage burn, the command and service modules would separate from the rest of the stack, using the service module's rocket. Once clear, the command module could separate from the service module and splash down.
• Mode III (aka Contingency Orbit Insertion) - Later in the stage 2 burn, orbit was achievable, so the 3rd stage and service module engines would be used to get into orbit.
• S-IVB to orbit - Similar to Mode III, but only the SIV-B stage is needed to get into orbit.
• Mode IV - This was for a problem in the SIV-B stage and uses just the service module to achieve orbit.
• Direct Abort Trajectory - For problems that might occur during the cruise to the moon, the service module would be used to turn the spacecraft around and direct it back to Earth.

Obviously, Apollo 13 was well past the point where the launch aborts could be used. The problem with using Direct Abort Trajectory was that the condition of the service module was unknown and it would have required jettisoning the LM. Since the ship and crew were almost into the zone of lunar influence, they re-established a free return trajectory to use the moon's gravity to return them to Earth. You can read more at Wikipedia's write up about the successful return of the crew.