Being an astronaut is a wonderful career. I feel very privileged. But what I really hope for young people is that they find a career they're passionate about, something that's challenging and worthwhile.

I thought the attractions of being an astronaut were actually, not so much the Moon, but flying in a completely new medium.

Two months after I got out of test pilot school, I saw an advert that said NASA was recruiting more astronauts. The best job you could have as a test pilot was being an astronaut, so I volunteered.

It doesn't matter if you want to be a teacher, an astronaut, or a reggaeton singer, you need to study.

My obsession with outer space is my way of being different. I make astronaut music. It takes an astronaut so long to get to space - that's how long it takes to catch up on my music.

I loved dinosaurs, I loved space, and I thought maybe I'd be the first paleo-astronaut.

No, I think most astronauts recognize that the space shuttle program is very high-risk, and are prepared for accidents.

Most of my family and friends are very familiar with the human space flight program and with the excitement of becoming an astronaut.

There are several revenue streams that are near and present that could support a private space station, including in-space manufacturing, microgravity research, and tourism - for both individuals and sovereign nation astronauts - and in-space supply logistics.

All space exploration is risky. As an astronaut, I had to decide each and every time I went to space whether or not to risk my life for the mission.

Manned spaceflight has lost its glamour - understandably so, because it hardly seems inspiring, 40 years after Apollo, for astronauts merely to circle the Earth in the space shuttle and the International Space Station.

The basic thing you have to understand is everything that happens on that spaceship, from the time you crawl into that seat to the time it touches down, is controlled from the ground. There's no one thing that makes a good astronaut. I don't know any person with determination and will that can't go to space.

I think most astronauts are not risk takers. We take calculated risks for something that we think is worthwhile.

Astronauts have been stuck in low-Earth orbit, boldly going nowhere. American attempts to kick-start a new phase of lunar exploration have stalled amid the realisation that NASA's budget is too small for the job.

I stayed in the astronaut program until 1993. People ask me why I left. I thought I had a lot of things to contribute that would be difficult to do if I stayed. I thought I could have a stronger voice as an advocate for space exploration. So I ended up starting my own technology consulting company.

There are no wishy-washy astronauts. You don't get up there by being uncaring and blase. And whatever gave you the sense of tenacity and purpose to get that far in life is absolutely reaffirmed and deepened by the experience itself.

The photographs of space taken by our astronauts have been published all over the place. But the eye is a much more dynamic mechanism than any camera or pictures. It's a more exciting view in person than looking at the photographs. Of course, I personally am sick and tired of hearing people talk like that: I want to see it myself!

Our astronauts, when they go orbiting around the earth, they actually come back slightly younger than a twin that they would have on the planet Earth who was stationary. This is called the twin paradox.

Astronauts are very professional and when they're preparing for launch, they prepare for it as the most serious endeavor of our lives.

It's very dangerous to put astronauts on a moon base where there's radiation, solar flares and micro meteorites. It'd be much better to put robots on the moon and have them mentally connected to astronauts on the Earth.

I was a frustrated astronaut all my life. I grew up at a time when space seemed to have no boundaries, and lots of us presumed humans would be living on the moon and landing on Mars.

We want to make sure we get living astronauts to the surface of Mars.

The images of Earth's delicate biosphere, contrasting with the sterile moonscape where the astronauts left their footsteps, have become iconic for environmentalists: these may indeed be the Apollo programme's most enduring legacy.

Sometimes people ask me how difficult the astronaut program was, but being in Sierra Leone, being responsible for the health of more than 200 people, seven days a week, 24 hours a day, 365 days a year, at age 26 - that prepared me to take on a lot of different challenges.