When astronauts make preparations for missions to the International Space Station (ISS), the advance training for specific tasks they will need to carry out on the ISS is quite crucial. But how does one simulate the environment of zero-gravity on the Earth?

NASA has answered this question with a large-scale set up of the ISS that it has built and placed in a huge swimming pool.

The Neutral Buoyancy Lab (NBL) is a NASA facility that is stationed at 20 minutes from the Johnson Space Centre. NASA has trained its astronauts to conduct extravehicular activities (EVAs) or known as spacewalks in underwater conditions. NASA has considered working for long below the surface in neutrally buoyant conditions as an ideal way to train for the zero-gravity in space.

The ISS mock up is 40 feet below the surface of the pool. You can see everything since the water is calm and crystal clear.

If you have ever done scuba diving, you would know that when one is neutrally buoyant and weighted in a way that you neither rise towards the surface nor sink to the bottom. You have good control in all three dimensions over how you move and where you are. It is quite like flying and it is also like what astronauts encounter in space.

During the Space Shuttle program, NASA astronauts were assigned missions and they would practice the missions underwater and take advantage of neutral buoyancy so that they get prepared for what it would be like in space.

Almost every day, two astronauts come to NBL for underwater sessions of six hours which is the normal time for the session. During the course of their training, they spend about six to eight hours in the pool for every hour of actual activity they are expected to do in space.