Delta IV launch vehicle growth options to support NASA's space exploration vision

One of the defining attributes of the Vision for Space Exploration is its emphasis on affordability, which is also linked to another key attribute-long-term sustainability. As applied to space-lift requirements, this overriding constraint may argue for system choices not optimized for architectural elegance but, rather, for lowest development or recurring cost. Affordability constrains most projects and, second only to safety, may be the most important factor in the success of the Vision for Space Exploration. Finding the most affordable space launch approach and designing the architecture for cost may be the key to shaping the overall exploration architecture for success.