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