Astronauts will perform another test on Friday to identify the source of a slow loss of air pressure on the International Space Station, NASA said Thursday.
NASA said the leak was continuing, contradicting a report from the Russian Interfax News Agency that quoted a Moscow mission control official as saying; "The pressure inside the station is stable."
Explaining the discrepancy, a NASA official said at one point on Wednesday pressure appeared to be stable. But measurements taken Thursday showed the space station was still losing pressure at the same rate it had been, leading managers to believe the earlier reading was an anomaly.
Ground controllers have determined the station has been losing pressure since Dec. 22.
On Friday, Russian astronaut Alexander Kaleri will test the system that removes carbon dioxide from the atmosphere and vents it into space to see if it has developed problems with its seals.
The Russians used the same hardware aboard the Mir space station and learned that it tends to develop leaks as it ages, NASA said.
NASA said the station's air pressure had fallen to 14.03 pounds per square inch and is approaching the level of 13.9 pounds per square inch at which pressure is too low for the optimal operation of some equipment on the orbiting lab.
No threat to astronauts
The drop poses no threat to the two astronauts on board, Kaleri and British-born NASA astronaut Michael Foale. NASA plans sometime in the next few days to re-pressurize the station using nitrogen stores already aboard.
Although the pressure loss is not dramatic, it is more than the five-year-old station has experienced before, and adds to a mounting list of problems that include faulty monitors for air and water quality and a broken gyroscope used to orient the spacecraft.
Ground controllers fired thrusters on the Russian spacecraft attached to the station for 5 minutes and 24 seconds on Thursday to lift its orbit by 1.5 miles (2.4 km). Such adjustments are needed periodically as the orbit decays over time.
The space station, weighing over 455 tonnes and covering the area of a football field, sinks about 660 feet (200 metres) every day. Its orbital height, about 230 miles (370 km) above the earth's surface, was last adjusted in October.
Russia has launched all manned and cargo ships to the outpost since February 2003, when the United States grounded its space shuttles after the Columbia shuttle broke apart,killing seven astronauts.
Kaleri spent much of Thursday dealing with another atmosphere issue. A Russian system for generating oxygen, once a suspect in the pressure leaks, failed completely after working intermittently for weeks.
The astronauts are already using a back-up system and have enough breathable air in reserve to last six months. NASA said there should be no trouble sending a replacement system with the next unmanned Russian cargo ship destined for the station.