Space Suits, Extravehicular Activity, and Underwater Training for Astronauts

A major reason why work is so difficult while wearing a space suit is the air pressure that must be maintained inside the suit. This makes it particularly difficult to move hands and fingers. Through the era of the space shuttle/International Space Station (ISS), space suits were designed to use pressures as low as possible. The drawback to a low pressure suit, however, is that astronauts preparing for a space walk must “pre-breath” pure oxygen for 2-4 hours (depending on whether they are exercising) or the pressure inside the space shuttle must be reduced prior to the space walk, in order to avoid decompression sickness resulting from nitrogen bubbles forming in the blood. This is one of the numerous physiological complications associated with human spaceflight. Thus, engineers are trying to develop higher pressure suits with particular emphasis on the fingers of the gloves.

“Walking “ in space is known as extravehicular activity (EVA). An important part of EVA training takes place underwater. For ISS-related activity, such underwater training takes place in NASA’s Neutral Buoyancy Laboratory (NBL). The NBL is an enormous pool, the largest ever built. Underwater in the NBL are mock-ups of ISS components, or whatever craft or components astronauts will be operating from, or on, during the EVA for which they are training. The Russian Federal Space Agency, Roscosmos, has a similar, though smaller, facility with mock-ups. It is used for astronauts and cosmonauts training to use the Russian space suits. Typically an astronaut spends 10 hours in the NBL for every hour that will be spent in EVA. Astronauts wearing space suits perform dive, assisted by professional divers in the pool who are diving with SCUBA equipment. During each simulated EVA, some divers are assigned to monitor and assist with equipment, while others provide direct assistance to astronauts or to others who are diving in space suits (sometimes non-astronauts have the opportunity to dive wearing a space suit, generally for research purposes).

If you examine the photograph, you will notice that at least seven divers are visible in proximity to the two people who are wearing space suits. Notice that one diver has his arm around the umbilical of one of the space suits. One of the many tasks that the NBL divers perform is to make sure that these umbilicals do not become entangled with one another or with equipment. Unlike during an actual EVA, when suits are pressurized from tanks attached directly to the suit, while in the NBL suits are pressurized through these umbilicals. Since the training takes place at depth, the pressure maintained inside the suits is much higher than the normal pressure at the Earth’s surface, while in space during an EVA, the pressure inside the suits is much lower than normal. This difference has important implications vis-à-vis the measures taken to prevent decompression sickness in the NBL vs. EVA situations.