Space architectures capable of supporting a permanent human presence on Mars are extraordinarily complex, with many different interdependent systems.

You need propellants to accelerate toward Mars, then to decelerate at Mars, again to re-accelerate from Mars to Earth, and finally to decelerate back at Earth. Accordingly, the mass of these required propellants, in short, drives our need for innovative launch vehicles.

NASA needs to focus on the things that are really important and that we do not know how to do. The agency is a pioneering force, and that is where its competitive advantage lies.

Buzz Aldrin Quotes