Breathing Easy on the Space Station
Making Oxygen From Water
Most people can survive only a couple of minutes without oxygen, and low concentrations
of oxygen can cause fatigue and blackouts.
To ensure the safety of the crew, the ISS will have redundant supplies of
that essential gas.
"The primary source of oxygen will be water electrolysis, followed by O2
in a pressurized storage tank," said Jay Perry, an aerospace engineer
at NASA's Marshall Space Flight Center working on the Environmental
Control and Life Support Systems (ECLSS)
project. ECLSS engineers at Marshall, at the Johnson Space Center and elsewhere are developing, improving and testing primary life
support systems for the ISS.
The Expedition One crew -- Bill Shepherd, Sergei Krikalev and Yuri
Gidzenko -- aboard the Space Station. During their four-month
stay, the crew will relied on the station's hardware to provide
Most of the station's oxygen will come from a process
called "electrolysis," which uses electricity from the ISS solar
panels to split water into hydrogen gas and oxygen gas.
Each molecule of water contains two hydrogen atoms and one oxygen atom. Running
a current through water causes these atoms to separate and recombine
as gaseous hydrogen (H2) and oxygen (O2).
The oxygen that people breathe on Earth also comes from the splitting of
water, but it's not a mechanical process. Plants, algae, cyanobacteria
and phytoplankton all split water molecules as part of photosynthesis
-- the process that converts sunlight, carbon dioxide and water
into sugars for food. The hydrogen is used for making sugars,
and the oxygen is released into the atmosphere.
"Eventually, it would be great if we could use plants to (produce oxygen) for
us," said Monsi Roman, chief microbiologist for the ECLSS project
at MSFC. "The byproduct of plants doing this for us is food."
However, "the chemical-mechanical systems are much more compact, less labor intensive,
and more reliable than a plant-based system," Perry noted. "A plant-based
life support system design is presently at the basic research and
demonstration stage of maturity and there are a myriad of challenges
that must be overcome to make it viable."