The blackness of space was a big shock to me. It is a deep, three-dimensional, oily blackness. You can feel the distance.

As an astronaut, when you're getting ready to go out of that hatch, you know that's the pinnacle of both your career and your life. The view completely blows you away. The real challenge is getting past the excitement and getting focused and down to work.

In 2009 I went up on the space shuttle. I was in space for 16 days and docked at the space station for 11 days. The entire crew did five space walks, of which I was involved with three of them. When you're doing a space walk, you always have a buddy with you. It's a very dangerous environment when you're doing a space walk.

We have to be plumbers, electricians, construction engineers, or workers, on the space station, but at the same time running a laboratory, being scientists, being the best laboratory assistants we can be. It's all in a bundle; it's very exciting, it's a lot of fun.

When we're on the space station, we orbit the Earth 16 times per day, which means we're constantly moving to and away from the sun. From light to shadow, the temperature swings by 300 degrees. Of course we're protected by the gear we wear, but you can definitely feel this temperature change.