The last time you were in space was 1994, and you were 47 years old. How old is too old for space travel?
There is no too old. One of my role models is former astronaut and Sen. John Glenn. He was 77 the last time he flew in space. Jean-Jacques Dordain, former head of the European Space Agency, and I have a deal: When we turn 77, we're both going to try to travel in space together.
U.S. astronaut Scott Kelly was 51 when he traveled aboard the International Space Station last year, and 52 when he returned 340 days later. Compare your experiences.
I am a space shuttle veteran, a space camper. I'm not sure that I could do what Scott Kelly did and come back like Superman; his condition was incredible after a trip that long. When I flew, we were still trying to figure out how to deal with muscle loss and bone loss, but we're overcoming those things today.
See Also: A Boomer’s History of Mars
Did you always want to explore space?
As a kid, I was fascinated by space flight, but never, ever, ever harbored any expectation that I would do it. It was a result of growing up in the segregated South and having been conditioned that there are things that you can do and things you cannot do. There were no blacks in the space program.
What changed your thinking?
I met Ron McNair, the second African American to fly in space. He asked if I was going to apply for the space program after Marines flight school, and I told him, "They'd never pick me." He looked me in the eye and said, "That's the dumbest thing I ever heard. How do you know if you don't ask?" He embarrassed me into filling out my application.
Mars is the new space frontier. Will you go?
I would love to. Fourteen years from now is about when we'll be ready to send humans to Mars. We still have work to do before deciding on a mission of many orbits or a landing on one of its moons.
NASA's unmanned Juno mission is scheduled to arrive at Jupiter on July 4, five years after launch. What are your hopes?
Its purpose is to orbit and study the planet for a number of years. Juno has giant solar cells, new technology, so this satellite is going to Jupiter on solar power. It is unique. We'll get closer looks at Europa, Jupiter's giant moon, where scientists believe there is a really good chance of life.
Will the Space Launch System you're building send us to Mars?
That's correct. We're building it to launch missions to deep space in a relatively short period. "Relatively" for reaching Mars is eight months.
Some people say an asteroid as large as the one that took out the dinosaurs could hit Earth.
We are actively identifying asteroids of all sizes, and there is no known civilization-destroying-size asteroid that will strike Earth.
Will your Asteroid Redirect Mission actually intercept one?
Yes, we're going to take a boulder from an asteroid and, over about a year and a half, push it into orbit around our moon. We're not capable of capturing a giant asteroid just yet, but we do want to demonstrate the principle of doing that.
Of your four flights in space, what moment is most memorable?
It's the entire experience of my last space mission, STS-60. It was NASA's first flight with a Russian cosmonaut member of our crew. We transplanted two Russian families to Houston. Now we have a coalition of 15 nations that runs the International Space Station.
So exploring space today is a collaboration?
It makes no difference what's going on down here on Earth. We operate in space as if we're all part of one human race focused on trying to get humans to Mars — farther than we've ever been before — this time to stay and continue our exploration.
Stephen Petranek is the author of How We'll Live on Mars and former editor-in-chief of Discover magazine.