Catapult: I've never heard about a catapult at the launch pad.
I wonder if the G forces involved hadn't decided NASA to chose the rocket instead. But I really don't know.
But it sounds an interesting idea.

Rockets unders the capsule for escape:
The kick would have to be such that it can't be used for a gentle ride.
Certainly not manoeuvring towards a station or another space platform.
Now, to reduce speed for re-entry...Perhaps this can work (but I don't think they would like the kick after having spent months in space; however, if the thrust can be smoothed, once in space...).

Regards

Raoul