The Neutral Buoyancy Laboratory (NBL) is an astronaut training facility located at the Sonny Carter Training Facility near NASA's Johnson Space Center. The NBL consists of a large indoor pool of water (40 feet deep, 202 feet long, and 102 feet wide. In other words, this is a big ass pool, of which I recently spent parts of 2 days learning boat- and helicopter-related survival training. And yes, I can honestly say that I trained with (or at least near) the astronauts!
We also had the chance (via a special visor) to see 2 astronauts perform simulated task in preparation for upcoming missions. Deep down in the pool are full-sized mock-ups of the International Space Station (ISS) modules and payloads, and visiting vehicles from other National programs.
The principle of neutral buoyancy is used to simulate the weightless environment of space. What we say was the astronauts (in 300# space suits) lowered and raised in and out of the pool using an overhead crane. Once in the water, the suited astronauts are weighted in the water by support divers so that they experience minimal buoyant force and minimal rotational moment about their center of mass. Multiple divers surround the astronauts during their entire training exercise. It was a very cool thing to watch and appreciate.
Postscript - Who was Sonny Carter?
M. L. "Sonny" Carter, was instrumental in developing many of the current space-walking techniques used by the astronauts. Carter was selected into the astronaut program in 1984 and flew into space STS-33 aboard the Space Shuttle Discovery. He was training as a crew member aboard STS-42 when on April 5, 1991, he died in a commuter plane crash near New Brunswick, Georgia. Before he became an astronaut, Carter was a Navy doctor and aviator, and a soccer player for the North American Soccer league. read more