The hardest thing for me as an astronaut was to improve my swimming skills.

Viewing our planet was so compelling. Words like beautiful and awesome just don't do it justice. I felt that I was looking at a paradise. I was looking at heaven. I can't imagine any place being more beautiful than our planet and how lucky we are to be able to live here.

I applied to be an astronaut four times. I was rejected three times before I was accepted. So, it's about that, not - following your dream and not giving up.

At every step of the way, when I had trouble, there were people that came in, in my life that helped me. It's important to go seek help when you need it, and to give help when other people need it. And that is really more important than coming in with a gigantic brain into the astronaut program.

To become an astronaut is not a question of being the best at something or things coming easy to you, but it's being a person that can work with others and not give up. And, for me, that was part of it too.

I was the first person to tweet from space, but now every astronaut tweets from space and does Instagram and Snapchat and Face - they have Facebook going. I think it's more of a personal relationship they have with space now. They see it as more obtainable than me watching my superhero Neil Armstrong and Buzz Aldrin walking on the moon. It's like, there's no way I can do that.

The hardest thing for me as an astronaut was to improve my swimming skills.