Space travel for me has always been something obvious and something that didn't need to be explained. I mean, I read Jules Verne of course when I was 9 years old, The Voyage to the Moon [sic], and I also wrote a little story based on Jules Verne myself with a similar theme. I mean, clearly that was in my mind from the age of 9, as obviously something we will do and it didn't need to be justified, it was just clearly, obviously a great adventure, and why not? So that was my background. Then afterwards, of course, I got interested in astronomy from a scientific point of view, but I think it's important to keep the two things separate, that there are two kinds of space activities: there's space... space science, which I'm very much concerned with; and there's space adventure or 'sporting events' in space, which I'm also concerned with, but they are very separate, and it was a great pity that the things became confused in the public mind. So we have, at the moment, a very successful space science programme which is done with automatic machines, with robots, with unmanned missions, which are much cheaper and much simpler; and on the other hand we have the shuttle programme which is using humans and which is supposed to be a big human adventure. But somehow the two things have got confused in the public mind, and... so the public thinks that the shuttle is doing science, which it actually isn't, and... and the public also thinks that the whole programme is in trouble because the manned programme is in trouble. But the reality is the manned programme is in trouble because it doesn't have any clear goals; the unmanned programme is doing fine. So my life has been sort of divided between these two compartments, and I like to keep them very separate. I think the science, the space science programme, is enormously exciting in itself. We are exploring the universe with these automatic machines, and of course the whole art of... automatic navigation and data processing has advanced by leaps and bounds since the 1960s, so what we can do now with an automatic probe at Jupiter or Neptune is so vastly more than we could have done with a manned mission in the 1960s. So there's no justification, from a scientific point of view, for manned missions. On the other hand, I still would love to go, and I think people will go, simply because it's in our nature as living creatures; that life has a tendency to occupy unoccupied niches, so I think life will spread into the universe, and we are just a part of that. And for me that's a basic... what Dirac would call a basic belief which doesn't need to be justified, that life has beautified this planet so enormously, and compared with this planet everything else in the universe is rather dull, and all the planets we observe are pretty boring compared with the earth because there's nothing living there. And if life could just expand out into the universe, the whole universe would just become vastly more diverse and vastly, vastly more interesting; and why shouldn't we do that? And we should be the midwives to make that possible.

[Q] Did at any stage the worry about diversity being constrained here on earth become likewise a factor?

That's of course a factor. I mean the earth is getting to be too small for us. We have great problems with the environment; we have great problems with the extinction of biological species; it's clear the earth is getting too small and it's we who are making it so, and of course we have to limit our population on the earth, we have to learn to live frugally, and that's absolutely clear. But in addition, we just need more real estate and there is all that beautiful real estate out there, and why not spread out? And that's... anyway to me, it's a question of when and not a question of why. And of course, it has to be cheap. I'm not interested in billion dollar missions to Mars. That seems to me a dead end, just as the Apollo missions to the moon were a dead end. They were too expensive to be sustained. So that's not the way to do it. But it will become cheap just because the technology improves all the time. But that's the end of the sermon. I think we should go back to the history.