Originally Posted by Don't Hang Up
"I think Saturn V had much more realistic abort options over the Shuttle. A solid fuel rocket motor was attached directly to the nose cone that contained the command module. The command module could therefore be dragged clear by this (to safe parachute and splashdown height).
Once the emergency escape rocket was jettisoned the vehicle was high enough for the whole Command/Service module to power itself clear of the main structure."
This is basically true, but the presumed safety factor of launch abort can be misleading. The launch escape tower is jettisoned early in the 2nd stage, which leaves the only a "mode II" abort option of separating CSM, which had a meager 0.32-to-1 thrust-to-weight ratio. The separation would have been very slow.
This almost happened on Apollo 13, when a severe longitudinal oscillation happened on the center engine of the 2nd stage. This was briefly shown in the movie. In the actual mission, later analysis showed the vibration was so severe it nearly caused structural failure. The center engine was vibrating with a fore/aft stroke of 3 inches -- and it's mounted on a large metal cruciform beam, similar to a skyscraper I-beam.
13 Things That Saved Apollo 13, Part 5: Unexplained Shutdown of the Saturn V Center Engine - Universe Today
Saturn V Also Suffered Engine Launch Anomalies : Discovery News
Instrumentation revealed the engine vibration peaked at 68 g. The cutoff was essentially a lucky event that probably saved the vehicle and possibly the crew. Had the 2nd stage broken up it's unclear if the sluggish CSM could have accelerated away safely.
While Apollo 13 was the only manned mission of that series that experienced a significant booster anomaly, the unmanned Apollo 6 also had severe pogo problems that would have probably triggered an abort. In that case it happened on stage 1, so they theoretically could have used launch escape, although it was at a very high dynamic pressure.
On the Skylab Saturn V launch, pyros failed to separate the interstage skirt between stage 1 and 2. On a manned mission this was officially an abort scenario since the additional weight would have prevented reaching orbit. Officially this would have been a tower abort, although I'm not sure a 12g abort would have been needed in that more gradual situation.
A non-obvious criteria governing Apollo abort rules is the reentry heating and g load must be survivable. The CM had a L/D ratio of about 0.3:1, so while it had some lift to modulate g and heat loads, there were otherwise possible abort trajectories that exceeded g or thermal limits. The goal was avoid these but I vaguely recollect there were conditions where abort initiation was possible but it was not survivable.
The Apollo Launch Escape System weighed about 8,000 lbs, vs the CM roughly 13,000 lbs -- 62% of vehicle weight. At a significant payload cost, it did provide an abort option over the first 25% of the ascent until it was jettisoned.