Peggy Whitson, PhD

Photo: Courtesy of NASA

5 of 11
Peggy Whitson, PhD
NASA's Most Experienced Astronaut (377 Days in Space)

On day three or four of my first orbit in space, I remember thinking, "I get to stay up here." It was this sensation of being in the right place. I knew then that I would be back. One hundred and eighty days later, it was still hard for me to leave.