I feel we need to remind the world about the Apollo missions and that we can still do impossible things.

I don't believe any pair of people had been more removed physically from the rest of the world than we were.

America must dream again, and have the faith to achieve the dream.

One of the major problems with long-term deep space human flight is the requirement for radiation shielding.

I think I need to continue to think and plan and marry all of the different things that we could do that make transportation in space from the earth to the space station, from the earth to the moon to space stations around the moon to visiting an asteroid.

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.

I remember it was hard to believe that I was taking a step onto the lunar surface.