It depends on just what job should be done. Some have made the case for exploration programs based on 20 ton-size payloads to LEO. It isn't just about asking for the biggest rocket possible.
For me the things a HLV should do in the future are Moon/Mars landing missions and in the long run carrying payload for a permanent base there. To do this with a 50 metric tons rocket would be hardly possible in the old fashioned "One-shot", but only with orbital assembling/upper stages in an orbit to dock. Which solution is the better one is questionable (We had this discussion already elsewhere
), but I think the HLV will win, simply because politicians want it: "Apollo was done this way, so why should we change it!" But we're in changing times with commercial spaceflight, maybe the next moon mission is not funded by politicians.
NOTE: I don't want to start this discussion again and if we really have to in the other thread
More to go wrong, but also more redundancy if something does go wrong. And also depends on what engines are being used, of course.
Frankly, engine failures at liftoff are quite uncommon, so the probability that something fails at that phase is not that high with 5/7 engines. I can't even remember an engine failure of an (American, I can't remember all Russian missions:uhh
manned launch except for the Pogo oscillations in the Saturn V and STS-51F's sensor failures, which are both not really engine failures afaik. So while a failure with that number of engines is quite uncommon, it's much more possible with four-times more engines. But the real question in that matter is: Can you safely switch of one engine or will one failure blow up the whole stack.
About redundancy: Redundancy might be there somewhat in the flight, but if I have a problem in the first few seconds your moon mission will make an Newton's apple reenactment, guess how wonderful that would be in the current funding situation of NASA.
