Neutral Buoyancy Laboratory

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An astronaut training in the NBL

The Neutral Buoyancy Laboratory or NBL is a training facility for astronauts maintained by NASA's Johnson Space Center in Houston, Texas. The NBL consists of a large pool of water in which astronauts may perform simulated EVA tasks in preparation for upcoming missions, for example, construction activities related to 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. in length, 102 ft. wide, and 40 ft. deep, and contains 6.2 million gallons of water.^[1]

One downside of using neutral buoyancy to simulate EVA is the presence of drag. Generally, this is overcome by doing tasks slowly in the water, to minimize the effect of drag on the exertion required to complete a task. Another downside is that astronauts are not weightless within the suit, and thus 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.