I just finished reading the Martian (have not watched the movie yet), and wonder what are the current (ie. after rescuing him) plans for the Ares IV mission? They certainly will not use the MAV which has been sent for their mission, as it is not exactly in best shape.

If they just send a new MAV as fast as possible to a nearby site (not exactly the same place though, there is a a lot of rubbish), will it be there early enough? Or do they need to reschedule the mission?

Did I just miss the discussion of Ares IV‘s feature, or does the book really do not state anything about that topic?