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I think that witnessing ecological problems visible from space is one of the new and essential roles of astronauts.

Sending people into space is very important culturally. That's really the justification. You cannot rationally justify it on the basis of the science and technology we get out of it.

With every inch of land on Earth now catalogued by our satellites, the stars are the next place we as a species must travel. And with a booming world population that will hit 9.1 billion in 2050, large-scale space travel may become a necessity.

You don't go into space just for the science. Economically, it is not worth it. I think the reason we should be in space is for the exploration; it's the human endeavour.

We've gotta reinvest in space travel. We should've never left the moon.

If you want a nation to have space exploration ambitions, you've got to send humans.

When you go to Mars, you need to have made the decision that you're there permanently. The more people we have there, the more it can become a sustaining environment. Except for very rare exceptions, the people who go to Mars shouldn't be coming back. Once you get on the surface, you're there.

Emigration is no longer a solution; it's a defeat. People are risking death, drowning every day, but they're knocking on doors that are not open.

Everyone who's been in space would, I'm sure, welcome the opportunity for a return to the exhilarating experiences there.