Space Station ( ISS )

Breathing Easy on the Space Station

Life support systems on the ISS provide oxygen, absorb carbon dioxide, and manage vaporous emissions from the astronauts themselves. It's all part of breathing easy in our new home in space.

A http://science.nasa.gov/

story by Patrick L. Barry

An artist's rendering of the ISS as it currently appears.
November 13, 2000 --

Many of us stuck on Earth wish we could join (at least temporarily) the Expedition One crew aboard the International Space Station (ISS). Floating effortlessly from module to module, looking down on Earth from a breathtaking height of 350 kilometers.... It's a dream come true for innumerable space lovers.

But be careful what you wish for! Living on the Space Station also means hard work, cramped quarters, and... what's that smell? Probably more outgassing from a scientific experiment or, worse yet, a crewmate.

With 3 to 7 people sharing a small enclosed volume on the still-growing Space Station, air management is critical.

Life support systems on the ISS must not only supply oxygen and remove carbon dioxide from the cabin's atmosphere, but also prevent gases like ammonia and acetone, which people emit in small quantities, from accumulating. Vaporous chemicals from science experiments are a potential hazard, too, if they combine in unforeseen ways with other elements in the air supply.
So, while air in space is undeniably rare, managing it is no small problem for ISS life support engineers.

In this second article in a series about the practical challenges of living in space, Science@NASA examines how the ISS will provide its residents with the breath of life.

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 breathable air.

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."

source: (NASA)

National Aeronautics and Space Administration