Mark Vande Hei, a retired Army colonel, waves as he is lowered into NASA's Neutral Buoyancy Laboratory pool near Johnson Space Center in Houston as part of training, March 1, 2017. The pool is one of the world's largest at 202 feet long and 40 feet deep, and is big enough to hold a replica of the International Space Station. Vande Hei is preparing for his first space mission, which is scheduled for mid-September. DoD photo by Sean Kimmons