Underwater spacewalks recreate the 'moon' in a giant NASA pool (photos)

a spacesuited diver grasps a bicycle-like vehicle in an underwater facility. the diver and the vehicle are on sand. to the right is an american flag planted in the sand. an oxygen hose trails behind the diver

Before walking on the moon, future astronauts may go for a swim.

The famed Neutral Buoyancy Laboratory (NBL) near NASA's Johnson Space Center in Houston has trained hundreds of spacewalkers since 1992. All International Space Station crews spend many hours by simulated space modules in the large, indoor pool of water. There, they gradually get used to floating, turning screws, mounting hardware and other activities — all within reach of trained safety divers.