NASA astronauts Bob Behnken and Doug Hurley will be the first to fly SpaceX's Crew Dragon spaceship. Here's how they're preparing.

· NASA astronauts Bob Behnken and Doug Hurley will be the first to fly SpaceX's Crew Dragon spaceship — and probably the first people in history to fly any commercial spaceship.
· SpaceX CEO Elon Musk recently said the duo could fly Crew Dragon to the International Space Station as early as April.
· Here's how the...