Exactly the way we are doing it now. Design the next spacecraft while the current one is still in use. In the operations gap between the vehicles, you use the existing crew to reconfigure the infrastruture and to train them.<br /><br />If you killed the shuttle, and then waited for development, you'd have a bunch of people picking their noses until IOC. <br /><br />Also, I have a feeling we will be seeing the shuttle and ISS being used to help develop the next craft and test out ideas.