Educator Features

Astronauts Take a Dive
Astronauts working underwater
Why do astronauts need to know how to swim? After all, there's no water in space. There is water on Earth, though, and much of the practice for space walks takes place underwater. Astronauts dive to the bottom of a 12-meter- (40-foot-) deep tank called the Neutral Buoyancy Laboratory (NBL) because it simulates conditions very close to the weightlessness of space.

Image to left: Working underwater helps the astronauts prepare for working in space. Credit: NASA

Anyone who's ever swum knows that your body works very differently underwater. Heavy objects move with ease, and your body feels light and tends to drift and float. This is similar to how it feels to be in the microgravity of space. This is a great way for astronauts to simulate activities. Every experiment or project that will be used while onboard the Space Shuttle or International Space Station (ISS) is tested underwater before it goes into space. Extra-Vehicular Activities (EVAs), also called space walks, are practiced underwater. Any task to be done in space will be rehearsed several times in the NBL. Practice makes perfect, and when the environment is as uncertain as space, it's a good idea to log as many practice hours as possible. There are several NBLs in the United States and Russia, but the majority of astronaut preparations take place at the facility at Johnson Space Center in Texas.

An astonaut getting into his space suit in prepartion for underwater training
Picture a large, indoor swimming pool. An Olympic-sized pool is 50 meters (160 feet) long. The NBL is 61.5 m (202 ft) long, 31 m (102 ft) wide, 12.1 m (40 ft) deep, and holds 234,650,000 liters (6.2 million gallons) of water. An Olympic-sized pool holds about 957,600 liters (253,000 gallons). The water is kept between 27 and 30 °Celsius (82-86 °Fahrenheit), and is recycled every 19.6 hours. The NBL is substantially larger than a large swimming pool, which stands to reason, given the large objects placed inside.

Image to right: Astronauts wear their space suits to simulate an actual space walk. Credit: NASA

Full-scale working models of the Space Shuttle and ISS robotic arms fit inside the NBL. This allows astronauts to practice any necessary maneuvers before they head into orbit. The fully constructed Space Station will be too large to fit inside, but all modules and experiment areas will easily fit in the pool. The full team of astronauts, suited up in modified space suits, may work on any given project. They are accompanied by a team of divers to help with any logistical issues that may arise. Voice communication systems are installed in the pool and in the space suits. Support staff on dry land can interact and advise the astronauts as their training proceeds.

A picture of astronauts and scuba divers underwater
Image to left: Scuba divers help the astronauts with their work. Credit: NASA

The pool is called the Neutral Buoyancy Laboratory because astronauts and objects are not weightless; they attain neutral buoyancy. That condition exists when objects have an equal tendency to float or sink. They seem to hover, rather than bob up to the surface of the water. Since people in swimming pools tend to float to the surface, astronauts (and other objects) are weighted so that they neither float nor sink -- that's neutral buoyancy.

Working in the NBL is similar to working in space, but there are two significant differences. The suited astronaut in the NBL isn't truly weightless. Even though buoyant, the astronaut feels his weight and body mass. Secondly, the drag, or friction, of water acts to hinder motion. If you've tried to run or sweep your arm in a swimming pool, you've experienced that drag. In space, objects move effortlessly with a small nudge, and continue moving until they encounter some sort of resistance. Despite these two barriers to experiencing true microgravity, the NBL is the best available method for long-duration EVA training.

An astronaut practices drilling underwater
Astronauts perform many tasks in the NBL, from repairing the Hubble Space Telescope, to maintaining the exterior functions of the ISS, to installing new hardware. They learn about how their bodies move differently, how certain scientific principles no longer apply in space and how to compensate for them while accomplishing their projects. The facilities of the NBL also provide testing for new materials, handholds and procedures to be sure they'll function properly in reduced gravity.

Image to right: Astronauts practice things like drilling to learn how their bodies might move differently in space. Credit: NASA

Besides the water facilities, the NBL features a control room with a variety of computerized monitoring devices so that the astronauts' training can be filmed and evaluated. It also allows for robots to be controlled and other interactive devices to be operated.

Lesson Links

Density Columns
+ View lesson

Sink or Float
+ View lesson

Toys in Space
+ View lesson

Convection Currents and Fire
+ View lesson

Published by NASAexplores