"Sometimes astronauts feel a little ill or get minor scrapes. I trained as a crew medical officer to ..." — John M. Grunsfeld

When people left on the Oregon Trail from St. Louis, they knew that only a fraction of them would make it to the West Coast. But they went anyway.

The Martian atmosphere is very thin. It's like our atmosphere at 100,000 feet.

I have dedicated my life to answering the great scientific questions of our time and to the incredible adventure of space exploration.

At the age of six, I declared that I wanted to be an astronaut. My mother thought that was just fine, as it would encourage me to learn science, and besides, there really was no chance I would ever actually become an astronaut.