The expense of getting into space is the rocket launch, the rocket itself. Rocket's right now, commercial rockets cost probably somewhere between $50, or $120, or $150 million per launch. And those are all expendable. That is, you've got to buy a new rocket for each launch. So, that really is the critical part. If there was some kind of really, a revolutionary breakthrough and the price of rockets fell by an order of magnitude, I mean, just imagine what that would do as far as getting access to more ordinary people.

One of my challenges was to try to photograph the Great Wall of China. And I did actually take some photos, but it was hard to discern the wall with the naked eye.

The Russians have been flying long duration crews since the early '70's. And in the early days, they've ended at least two missions early because of conflicts within the crew. So, they learned early on the importance of studying this and making sure you put the right crew together. Since we began our work together on the International Space station with the Russians in the early 2000's, NASA has started to learn the importance of this kind of work. And so, I think it's important work and we are not fully onboard and recognize it as important.

One day, people will be able to buy tickets to visit space.

My advice for an aspiring astronaut is to really follow your passion. I mean, study something that interests you, but also qualifies you to apply. NASA recruits from a wide variety of backgrounds. I know people who have applied to be an astronaut who ask me, well should I do this or should I do that. And I said, you know, it doesn't matter. The basic requirements are you have to be in good health, and you have to have a good heart, I mean in a technical way, not to be a kind person, well that helps. Study something that you like and do well in it.

What keeps me up at night? Probably most, thinking about the future for my kids. It sounds kind of funny, but not so much what they're going to do, but how as a parent, how my wife and I as parents, how best we should prepare them for the world. And I know everybody does this, I think everybody stays up at night thinking about the best thing for their kids, and astronauts are no different.

Richard Branson is probably the most visible of the private commercial space guys, and what is venture, Virgin Galactic is about is sub orbital flight. That is, you'll see a spacecraft that looks more or less like an airplane and it will fly into space, but only spend about 15 minutes. It'll go up in a parabolic arc and then fall back down, and so the customers on that flight will only get about five minutes of weightlessness. They'll get to glimpse the horizon of the Earth, take a look at it before just before they start coming back down into the atmosphere.