Since the mid-90s, swimming has been an essential exercise for astronauts. That’s not because a large mass of water had been discovered in space in that decade, but because since then it has been a fundamental part of the training NASA astronauts undergo in a giant swimming pool.
On land, the best way of experiencing a similar sensation to zero gravity is to move underwater. So that the space crews could get used to weightlessness, in 1995 the American space agency constructed an indoor pool 61 metres long, 31 metres wide and 12 metres deep near the Johnson Space Center in Houston, Texas.
This infrastructure is bigger than an Olympic pool and is known as the Neutral Buoyancy Laboratory (NBL). The 234,650,000 litres of water that fills it is kept at a temperature of between 27 and 30 degrees centigrade, and is renewed every 20 hours. At first sight, the tank looks like a large sports swimming pool, but there is something hidden under the surface that few people would expect to find at the bottom of a pool: a replica of the International Space Station.
The NBL plays an essential role in the training of astronauts who are preparing for a mission. For instance, when a crew has to be sent to repair a component of the space shuttle or update the station’s computer system, the mission is practised a number of times in the laboratory’s pool.
In order for the conditions underwater to be as similar as possible to the environment in space, weights are added to the astronauts’ suits and the submerged components so that they are kept in a state of neutral buoyancy and prevented from floating or sinking. In addition, receptors similar to those that the crew members will use on the mission are fitted to their suits so that they can become familiar with the communications system.
Despite all of these efforts, there are two aspects of a space environment that are impossible to replicate. The first is the absence of friction. In space, when an object moves it does so continuously until it comes across some kind of resistance. In contrast, in the NBL pool, the water’s friction slows down movement. Secondly, in space astronauts do not feel their weight or body mass, which they do underwater.
Since the NBL was set up in Houston, similar water facilities have been built in other parts of the United States and Russia, although none as big as in this Texan city.
In this 360-degree immersive virtual reality video, you can experience what it is like underwater in the Neutral Buoyancy Laboratory.