Concerns over oxygen supplies on board International Space Station thought to be behind latest delay

Russia has again postponed the launch of Soyuz TMA 5 to the International Space Station (ISS) from 11 October for a "few days", citing a "malfunction in one of the craft's systems". But the delay could be motivated by concerns that the ISS may have to be evacuated before year-end unless at least one of three non-operational Russian oxygen generators can be brought on line.

An Elektron oxygen generator aboard the ISS has failed again, following a repair using spare parts that would have been used to bring a back-up system into operation. Of the three Elektron units on board the space station, the last one is "hard broken", NASA sources say. The other, although broken, was thought to be repairable using a jury-rigged bypass pump sent up on a Progress tanker - but the parts were used in the attempt to repair the prime generator.

NASA admits that if Russia cannot launch a new oxygen generator to the ISS before the end of the year, the space station may have to be abandoned if onboard reserves of back-up oxygen fall below 45 days. The ISS has about 162 days of back-up oxygen and there is no reason to doubt that two new Progress Ms will be able to carry new oxygen supplies, but delivery of a new oxygen generator is unlikely until February 2005.

The worst-case scenario is that the failure may force NASA and the Russian Space Agency to cancel the October launch, leaving the current expedition crew aboard until it may become necessary for them to abandon ship in the attached Soyuz TMA. The Progress tanker currently docked to the ISS has full oxygen and air tanks worth 100 days. Further oxygen is available in two high-pressure tanks in the US airlock and 84 solid-fuel oxygen generator canisters, adding a 42-day supply. This is enough to support the next crew, but there is no guarantee there will not be serious safety issues if the Elektrons cannot be repaired or replaced.

The ISS expedition crew awaiting launch may still be able to repair one of the two prime generators aboard the station. The second needs more extensive repair or replacement. A third back-up unit does not work. NASA will not be able to supply stored oxygen via refillable tanks until after the Space Shuttle has returned to flight and ISS Assembly Phase 1 has been completed in 2006.

If abandoned, the ISS could remain empty for months, says NASA, which admits there is a 50% chance of losing the $100 billion station if there is no crew on board to troubleshoot problems. The ISS has been manned continuously since November 2000 and assembly is due to be complete by 2010.


Source: Flight International