You could power the entire United States with about 150 to 200 square kilometers of solar panels, the entire United States. Take a corner of Utah... there's not much going on there, I've been there. There's not even radio stations.

It was obvious to me that we could never colonize Mars without reusability, any more than America would have been colonized if they had to burn the ships after every trip.

People work better when they know what the goal is and why. It is important that people look forward to coming to work in the morning and enjoy working.

The lessons of history would suggest that civilisations move in cycles. You can track that back quite far - the Babylonians, the Sumerians, followed by the Egyptians, the Romans, China. We're obviously in a very upward cycle right now and hopefully that remains the case. But it may not.

Mars is the only place in the solar system where it's possible for life to become multi-planetarian.

In order for us to have a future that's exciting and inspiring, it has to be one where we're a space-bearing civilization.

Life is too short for long-term grudges.