Every project shoudl have a means of envisioning its successful conclusion - answering the question "what does done look like?"
Here's NASA's vision of a successful conclusion of the Crew Exploration Vehicle. The trouble of course is that this "vision" is a really nice rendering of the hardware, software and operations of the mission. The details remain to be implemented.
As the contractors build their proposals for fulfilling this vision, these details emerge in the technical, programmatic and cost models of the solution.
