ISS Oxygen Generator Functioning in Backup Mode

Expedition 11 commander Sergei Krikalev works with the Russian-built Elektron oxygen generator aboard the ISS on May 5, 2005. Nearing the end of its life expectancy, the generator has failed for good according to ISS managers. CREDIT: NASA/JSC.

After four months of down time, the primary oxygen generator aboard the International Space Station (ISS) is back online.

Space station commander Sergei Krikalev and flight engineer John Phillips, the eleventh ISS crew, reactivated the orbital laboratory's oxygen generator Monday at 9:41 a.m. EDT (1341 GMT), NASA officials told SPACE.com.

While the generator appeared to function normally at first, it had failed into backup mode by the day's end, NASA spokesperson Kylie Clem said.

"It is still running," she said.

The Russian-built oxygen generator, known as an Elektron device, produces oxygen and hydrogen from water through electrolysis. Despite a series of repairs, the station's Elektron failed in May 2004.

Last week, Krikalev replaced the Elektron's liquids unit with a spare that arrived at the ISS aboard the unmanned Progress 19 resupply ship on Sept. 10 in order to repair it. The astronauts, as well as U.S. and Russian flight controllers, continue to monitor the system.

While the Elektron device was offline, Krikalev and Phillips relied on oxygen supplies stored in tanks aboard the ISS and the unmanned Progress cargo ships. Before the arrival of Progress 18, which docked at the ISS in June, the two astronauts also used solid fuel oxygen generator "candles" to maintain their atmosphere.

Krikalev and Phillips were never in any danger of running out of oxygen, NASA officials said at that time.

The ISS Expedition 11 astronauts are nearing the end of their space station mission and are expected to return to Earth aboard their Soyuz spacecraft on Oct. 10 EDT, though it will be Oct. 11 local time at their Kazakhstan landing site when they touchdown. Returning to Earth with Krikalev and Phillips will be U.S. scientist and entrepreneur Greg Olsen, who is paying $20 million to become the third space tourist to visit the ISS.

Olsen will fly to the space station with NASA astronaut Bill McArthur and Russian cosmonaut Valery Tokarev, the crew of ISS Expedition 12. Their Soyuz spacecraft will launch toward the ISS on Sept. 30 at 11:54 p.m. EDT (0354 Oct. 1 GMT) from Baikonur Cosmodrome in Kazakhstan.

• Complete Coverage: ISS Expedition 11
• Complete Coverage: ISS Expedition 12