During emergency circumstances - if additional people are aboard during a space shuttle mission or crew exchange, or if oxygen is lost through experiments or airlock depressurization, for examples � the Oxygen Generation System, as it is called, could provide an additional eight pounds of oxygen per day, for a maximum output of 20 pounds.

Like the Elektron system currently used on the station, the OGS relies on electrolysis, which splits water into its constituent oxygen and hydrogen. The oxygen is released into the station atmosphere, and the hydrogen is discarded into space. The OGS offers a higher oxygen-production capacity than Elektron and will provide important backup capability for supplying oxygen to the station crews.

At first, the OGS will use water carried to the station aboard shuttle Discovery, which is due to launch in July. Eventually, the device will draw water from the station's new Water Recovery System, scheduled for launch and to become operational before the first six-person crew arrives in 2009.

Together, they will form a closed-loop regenerative life-support system, which will recycle wastewater generated on the station for both drinking water for the crew and fuel for the OGS.

"Once complete, the regenerative life-support system will sustain additional crew members onboard that can conduct more scientific research," said Mike Suffredini, station program manager. "It also will give us experience operating and sustaining a closed-loop life support system similar to that necessary for future human spaceflight missions farther from Earth."

During the STS-121 mission, astronauts will move the OGS from the Italian-built multi-purpose logistics module Leonardo into the U.S. Destiny laboratory module.

NASA is planning to have the new system up and running as early as spring 2007.

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