Martin Rees

When I have a creative insight, there is a high. I think back in the day, I made music as much as I did because it made me feel so good. I think you could argue that there is a creative addiction - but, you know, the healthy kind.

Supplying fuel for a Mars expedition from the lunar surface is often suggested, but it's hard to make it pay off - Moon bases are expensive, and just buying more rockets to launch fuel from Earth is relatively cheap.