Most people never believed in the real possibility of going to the moon, and neither did I until I was in my twenties.

I feel we need to remind the world about the Apollo missions and that we can still do impossible things.

I was given permission to serve myself Communion, with wine and a wafer, on the surface on the Moon. But I was advised not to say anything about it at the time. Someone had strongly objected to the Apollo 8 crew reading from the Bible. We didn't want to get into any further trouble with the religious critics.

It's been one of the greatest challenges that ever came along in my life; it was one of the more difficult things to do.

As someone who flew two space capsules and twice landed in the ocean, I can attest from personal experience how much logistics work is needed to get you home.

I have no doubt that humans will go to Mars. And I feel that America has led so many things in space - we have invested so much, and we have a lot to gain - that America could and should be the nation that should lead the settlement of Mars.

Every couple of years, we could dispatch people from Earth to Mars.