"I was motivated to improve the U.S. strategy of going back to the moon in 1985. That's a long time ago. Going back to the moon would be a great achievement for tourism adventure flights."

"We must still think of ourselves as pioneers to understand the importance of space."

"The much-hyped Ares 1-X was much ado about nothing."

"Being first outside the spacecraft would bring much more responsibility, and I really wasn't looking for that."

"Before deciding what to do about national space policy, Obama set up an outside review panel of space experts, headed up by my friend Norm Augustine, former head of Lockheed Martin and a former government official."

"I think there would be no shortage of applicants to the government astronaut corps to be settlers on the planet Mars. And I think this would be very inspiring."

"The guys who walk on Mars are going to be historic."

"Instead of planning the retirement of the Space Shuttle program, America should be preparing the shuttles for their next step in space: evolving, not shutting them down and laying off thousands of people."

"The first footfalls on Mars will mark a historic milestone, an enterprise that requires human tenacity matched with technology to anchor ourselves on another world."

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

"I wrote 'Reaching for the Moon' because I wanted to tell kids that all of us have a moon, a dream, that we can strive for. Even if you don't attain it, you can at least reach for it."

"It's time to open the space frontier to citizen explorers."

"Walking around on the moon was significantly easier than we'd thought it would be. There weren't any balance problems, so you weren't tumbling over."

"I know: If you're looking down at Earth, you're looking through an atmosphere that has a bit of haze in many places and not just occasional clouds."

"My favourite thing to do on this planet is to scuba dive."

"Retain the vision for space exploration. If we turn our backs on the vision again, we're going to have to live in a secondary position in human space flight for the rest of the century."

"The life expectancy of people going to Mars may be decreased by the higher level of radiation that they receive."

"Going to Mars would evolve humankind into a two-planet species."

"I think it's inevitable that there will be Earthlings establishing a presence on Mars. And I would say that it would certainly take place by 2050 or shortly thereafter."

"Exploring Mars is a far different venture from Apollo expeditions to the moon; it necessitates leaving our home planet on lengthy missions with a constrained return capability."

"I suggest that going to Mars means permanence on the planet - a mission by which we are building up a confidence level to become a two-planet species."

"When we get there, if we don't find any life on Mars, from that point on there will be life on Mars because we'll bring it there, whether it's germs and leftover urine bags, whatever it is."

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

"My expertise is the space program and what it should be in the future based on my experience of looking at the transitions that we've made between pre-Sputnik days and getting to the moon."