Underwater space training

How astronauts are prepared for danger-filled space missions in NASA’s Neutral Buoyancy Lab.

Training for the weightlessness of space is a major undertaking on NASA’s part that requires a dedicated test facility and a battery of cutting-edge equipment. As zero gravity free-fall on a specially adapted flight isn’t practical for long training periods and anti-gravity ‘machines’ are set to remain the stuff of science fiction, NASA uses the 23.5-million-litre (6.2-million-gallon) giant swimming pool at its Neutral Buoyancy Lab in Houston, Texas.

Neutral buoyancy itself is a property of an object that gives it an equal tendency to float to the surface as it does to sink to the bottom, so that it appears to hover in the same place in water. This property of neutral buoyancy is very similar to the weightlessness endowed by the lack of gravity in space: an astronaut wearing a neutral buoyancy suit in the pool is easily manipulated, just like they would be in space, but there are some key differences. The water drags on the astronaut to make movement and certain actions (like keeping an object still) more difficult than it would be in space, while making it easier to set an object in motion. The other problem is that astronauts aren’t truly weightless and can still feel the weight of their bodies while in the suit. For both these reasons, performing any tasks slowly and an awareness of the NBL pool can help minimise these limitations.

The 12.2-metre (40-foot) deep pool is primarily used for extra-vehicular activity (EVA) training. Astronauts, particularly those embarking on a mission to the International Space Station, practice full space walks lasting five hours at a time, manipulating objects and moving around large-scale mock-ups of the craft they will be working on. The fully completed ISS, at 107 x 73 metres (350 x 240 feet), wouldn’t fit inside the NBL’s 62 x 31 metre (202 x 102 feet) pool, but smaller replicas of the module the astronauts will work on are effective enough to train with. The current standard for NASA is that astronauts, depending on the difficulty of the EVA, spend five to seven times the amount of time training in the NBL as they would for the actual EVA.

The suits each astronaut wears for the NBL pool are very similar to those used on an EVA. Many of the suit components have, in fact, been salvaged from space suits that have already seen some EVA action in orbit on the ISS. Apart from the addition of weights and floats to give the suit with its wearer inside the property of being neutrally buoyant while in the water, NBL suits are distinguished by their life support and environmental control systems. These are self-contained with space EVA suits but while training in the pool, they’re provided by an umbilical cord attached to an external machine that supplies electricity, water coolant and pressurised breathing gas.

Naturally, safety and the health of the astronauts-in-training is carefully observed while in the pool. Although the dives aren’t particularly deep (12 metres/40 feet, while deep for a swimming pool is considered a shallow dive) they are for long periods of time. So the NBL has a full complement of medical staff on hand consisting of two physicians, two paramedics and 12 physiology personnel. The NBL also has a hyperbaric chamber on-site to treat any diver suffering from decompression sickness — otherwise known as ‘the bends’.

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