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.

My odyssey to become an astronaut kind of started in grad school, and I was working, up at MIT, in space robotics-related work; human and robot working together.

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

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.

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.

Astronauts cannot pick their nicknames and can only get their nicknames from other astronauts. Any astronaut who tries to give himself a cool nickname will regret it by getting just the opposite from his astronaut friends.