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Raytheon supports facilities and operations for astronaut training at NASA's Johnson Space Center (JSC) and Sonny Carter Training Facility in Houston. Under the JSC contract, Raytheon Technical Services Company (RTSC) provides subcontractor management and engineering support for training conducted in NASA's Neutral Buoyancy Lab (NBL).

The NBL is a 202-foot long, 102-foot wide, 40-foot deep pool filled with 6.2 million gallons of water. Located in Houston, it is used to train astronauts to perform EVAs (Extravehicular Activities) — NASA-speak for spacewalks. The NBL is used to simulate the zero-gravity conditions experienced by crew members. Raytheon engineers design the structural mock-ups used in the training to simulate actual hardware the astronauts will work on in space.

During EVA training, the astronauts are assisted in their activities by support divers provided under the contract. When training for an EVA, the crew member will wear an Extravehicular Mobility Unit (EMU), also known as a space suit.

Creating Neutral Buoyancy in the Lab
Support divers take the EMU to the bottom of the pool. Using weights and foam, the EMU is properly weighted and balanced so that it and the crew member will float neutrally in the water, thus giving the facility its name, the Neutral Buoyancy Lab. The crew member will neither float to the surface nor sink to the bottom. This simulates the weightlessness experienced in space. Of course, this is not exactly identical to space because if the astronaut is in a head-down position in the NBL, blood will still rush to the head and make the astronaut very uncomfortable, which would not happen in orbit. Also, the water provides drag against the suit, which slows movement. If the astronaut is kept in an upright position and moves at a slow pace, he or she remains very comfortable and can work for long periods of time under water.

Using Nitrox to Ensure Health and Safety
Crew members may be under water for more than six hours. Support divers are limited to three hours of in-water time per activity, with a 90-minute out-of-water surface interval. They then can complete two more hours in the water, for a maximum of five hours per day.

Being under pressure for long periods of time can cause certain health risks to divers. As a reference point, the air at sea level is 21 percent oxygen and 79 percent nitrogen. The weight of the water causes increased pressure on the divers' bodies and forces nitrogen from the air they breathe into their tissues and blood. The longer a diver spends in the water under pressure, the greater the amount of nitrogen will be stored in the diver's body. When the diver returns to the surface, the extra nitrogen that has built up in the body wants to form bubbles in the blood and tissues.

Divers refer to this condition as "the bends." This is extremely dangerous and can cause anything from severe discomfort to death.

One way to prevent the extra buildup of nitrogen in the body is to reduce the amount of nitrogen in the air. At the NBL, the divers and crew members breathe a special mix of oxygen and nitrogen, known as nitrox, which is mixed in the facility by RTSC subcontractor Oceaneering Space Systems. The NBL nitrox mix is 46 percent oxygen and 54 percent nitrogen. This increased oxygen level allows the crew members and divers to stay under water for long periods of time without the risk of getting the bends.

For years, divers have been using nitrox to increase the length of time they can stay under water. However, for most divers and equipment, the limit is 40 percent oxygen due to the fact that mixes of nitrox with higher than 40 percent oxygen are flammable; when oxygen at levels higher than 40 percent comes into contact with hoses and lubricants, it can cause a fire. For this reason, all of the equipment used for diving in the NBL is specially selected, cleaned and prepared to work in environments with higher than 40 percent levels of oxygen — which includes the NBL's 46 percent oxygen mix.

The NBL nitrox mix allows the NBL crew to safely perform training operations. Crew members have been trained to perform activities such as repairing solar arrays, inspecting heat tiles, assembling the International Space Station and making much-needed repairs to the Hubble Space Telescope. The NBL crew knows it has done its job when a crew member makes a comment such as, "The only difference between training in the pool and working in orbit is the view."

John W. Collins