The first problem we would need to overcome is defining a goal. Right now we have none. Once you have a very specific goal defined you can start defining the things you need in order to achieve it and begin the work towards that goal.We didn't wake up one morning and build a Saturn V rocket. We, instead, defined the specific hurdles we would need to overcome to get to the moon, then we worked on those, one at a time. Long before Apollo we had un-manned launches to prove heavy lift technologies. Then came Mercury to prove life support, communications, navigation, etc. Next was Gemini to deal with more complicated issues such as EVAs. None of this even takes into account the early un-manned Saturn rocket (Saturn I thru IV, and variants) tests.All of this, just for one primary goal. Go to the moon.You cannot just say "we need manned space flight", you need a specific goal that is clearly defined and achievable.Then, and only then, can we start talking about the technologies necessary, and the cost required, to accomplish it. Until that time, I have no problem with retiring the shuttle, there is no real reason to continue with it and lots of good reasons not to.