I want to keep on the move, keep stimulated and challenged.

The way I see it, commercial interests should manage a lunar base while NASA gets on with the really important task of flying to Mars.

To move forward, what's required is a unified space agenda based on exploration, science, development, commerce, and security.

Certainly, I've never wanted to live on past achievements.

My family has always supported my activities, whether it was doing combat in Korea, flying progressively and challenging fighter-jet aircraft in Europe, or studying for a doctor's degree at MIT. They have been always very supportive and understanding of the challenges and risks involved in my career. A family needs to work as a team, supporting each other's individual aims and aspirations.

The first footfalls on Mars will mark a historic milestone, an enterprise that requires human tenacity matched with technology to anchor ourselves on another world.

I don't think we're going to build a 50-person spacecraft or a 100-person spacecraft.