The Neutral Buoyancy Laboratory (NBL) is an astronaut training facility located at the Sonny Carter Training Facility and maintained by NASA's Johnson Space Center in Houston, Texas. The NBL consists of a large indoor pool of water, the largest in the world, in which astronauts may perform simulated EVA tasks in preparation for upcoming missions. The NBL contains full-sized mock-ups of the Space Shuttle cargo bay, flight payloads, and the International Space Station (ISS).

The principle of neutral buoyancy is used to simulate the weightless environment of space. Suited astronauts are weighted in the water by support divers so that they experience no buoyant force and no rotational moment about their center of mass. The suits worn in the NBL are down-rated from fully flight-rated EMU suits like those in use on the space shuttle and International Space Station.

The NBL tank itself is 202 ft. (61 m) in length, 102 ft. (31 m) wide, and 40 ft. 6 in. (12 m) deep, and contains 6.2 million gallons (23.5 million litres) of water. Divers breathe nitrox while working in the tank.

One downside of using neutral buoyancy to simulate microgravity is the significant amount of drag presented by water. Generally, drag effects are minimized by doing tasks slowly in the water. Another downside of neutral buoyancy simulation is that astronauts are not weightless within their suits, thus, precise suit sizing is critical.

The other primary method used by NASA to simulate microgravity is the so-called "Vomit Comet", an aircraft which performs a number of parabolic climbs and descents to give its occupants the sensation of zero gravity. The vomit comet reduces the problem of drag in weightless simulation. The main shortcoming of this method is its time limitations - periods of weightlessness are limited to around 25 seconds, interspersed with periods of acceleration of around 2 g as the aircraft pulls out of its dive and readies for the next run. This is obviously not suitable for practicing EVAs, which usually last several hours.

The Neutral Buoyancy Research Facility at the University of Maryland's Space Systems Laboratory performs research into EVA techniques and robotic interaction using neutral buoyancy as a basis for weightless simulation.

See also

• Yuri Gagarin Cosmonauts Training Center

References