The Elektron generates oxygen by recycling wastewater. Although the Elektron is the station's primary oxygen-generation unit, the ISS also can draw upon oxygen from tanks on Progress supply vehicles, its own airlock tanks, or from oxygen-generating candles, according to ISS Program Manager Bill Gerstenmaier. These backup systems combined can generate approximately 162 days of breathable air for a two-man crew, he said.

The current problem with the Elektron is thought to be the result of a clog in a hydrogen vent valve. If the Elektron can't be repaired, air and other consumables could be "a little tight" by the time the next Progress resupply vehicle arrives in December, Gerstenmaier said.

At about 45 days of breathable air remaining, the ISS program will begin thinking seriously about contingency plans, including the possibility of evacuating the station, Gerstenmaier said. The earliest that a replacement unit could be sent to the station would be on a Progress flight in February, he said.

Meanwhile, Expedition 9 Commander Gennady Padalka and NASA ISS Science Officer Mike Fincke continue to prepare for the arrival of the Expedition 10, which is scheduled to launch on a Soyuz Oct. 11 from Baikonur Cosmodrome in Kasakhstan.

Expedition 10 crewmembers Cosmonaut Salizhan Sharipov and U.S. astronaut Leroy Chiao will be accompanied on the flight by Cosmonaut Yuri Shargin, who will return to Earth with the Expedition 9 crew on Oct. 20.