Our biggest problem is that the Apollo crash program style still has an unshakeable grip on the imagination of both the Political classes and the NASA bureaucrats. That is not the model we should be pursuing. Instead of a ultraheavy lift rocket, like the SLS, shooting everything in one package, we should be using medium lift rockets of the Falcon 9 or Titan IV to put up fueling depots in LEO, then using the ISS as a terminal where ferries dock, discharge passengers, and they board dedicated deep space ship that will take them first to the lunar colonies, and then once we have built all the infrastructure and figured out how to survive long-term in space and on hostile planets using the moon, then off to Mars and the Belt. Once the infrastructure is built, everything will start happening quickly.