The primary system for generating oxygen on the Russian space station Mir broke down last week, forcing cosmonauts to use a backup system that can supply oxygen for the next two months.
The backup system is the same system that triggered a brief fire on the station last month that caused minor damage to the 11-year-old station.
One of the twin Elektron units that generates oxygen from waste water on Mir failed early last week because of too much air in the system, according to reports. The second unit, activated when the first failed, was shut down on March 7 when too much hydrogen was detected.
With both Elektron units shut down, the three men aboard Mir have turned to the backup system of lithium perchlorate cartridges, or "candles". These are normally used to supplement the primary oxygen systems when more then three people are on the station.
On February 23, one of these canisters caused a small fire which burned for about 90 seconds before cosmonauts extinguished it. The fire did damage some hardware, but caused no injuries. Russian authorities traced the cause of the fire to a crack in the cartridge, which allowed its hot contents to leak out and trigger the fire.
There are about 185 candles on the station, with at least 100 in good enough condition to be used. One or two of these candles will be burned each day to generate enough oxygen for the two Russians and one American on Mir.
"You hate to see your margins reduced in any area," Frank Culbertson, who heads NASA's shuttle-Mir program, said. "Its not a comfortable situation to be in, but that's where they are right now."
Russian engineers are working on repair plans for the Elektron units, and plan to have those plans ready by late March, when a Progress resupply craft is scheduled for launch to Mir. The resupply craft could carry any parts or tools needed to repair the units.
The problem is the latest to hit the aging space station. Earlier last week, Russian controllers failed to dock a used Progress resupply capsule to Mir. The Progress M-33 capsule had been docked to the station since November, but was undocked earlier in the month to allow a Soyuz spacecraft carrying three cosmonauts to dock with the station.
After several attempts to redock the capsule with Mir on March 4 failed, Russian officials decided not to try again. Instead, the capsule burned up in the Earth's atmosphere over the South Pacific east of New Zealand on March 12.
The station can also no longer communicate with ground controllers through communications satellites in geosynchronous orbit. One Russian satellite used for communications, Altair-1, has failed, while an antenna on Mir used for communications with another satellite is no longer working.
The Mir crew currently communicates with mission controllers via ground stations in Russia and the United States. Repair parts for the Mir antenna will be brought to the station on the next resupply mission.
The current Mir crew includes American astronaut Jerry Linenger, who has been on the station for two months, and Russians Vasily Tsibliev and Alexander Lazutkin.
Tsibliev and Lazutkin have been on Mir since last month. They replaced cosmonauts Valery Korzun and Alexander Kaleri, who returned to Earth with German guest cosmonaut Reinhold Ewald on March 2.