A leaky hose in a window of the laboratory module Destiny has been blamed for the International Space Station’s three-week drop in air pressure.
The hose, used to equalise pressure and eliminate fog between two of the window’s six clear panes, has been capped according to NASA. The hose has yet to be unequivocally confirmed as the source of the leak, but the station’s air pressure does seem to have now stabilised.
US astronaut Michael Foale and Russian cosmonaut Alexander Kaleri have been searching for the leak since they were told about it on 5 January. On 9 January they ruled out a Russian air purifier, and over the weekend they checked airlocks on the US and Russian station segments, as well as the docked Russian Soyuz lifeboat – all of which appeared airtight.
On Sunday, Foale returned to the US-built Destiny lab that he and Kaleri had checked with an ultrasonic leak detector a few days earlier. Both crew members initially thought they had heard a suspicious hiss from the window on that first check, but they concluded the noise was from a nearby science experiment.
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However, Foale used the stethoscope-like detector again on Sunday to check the hose, which is called a vacuum jumper. “I got a pretty strong signal when I flex the vacuum jumper,” Foale told mission control, according to MSNBC.
Critical level
“The news couldn’t have come at a better time,” mission control told the crew. The station’s air pressure had dropped from the normal 14.7 psi to 14.0 psi.
NASA have emphasised that the crew’s health was not in danger, but some onboard equipment, including an air monitor, is only certified for use above 13.9 psi. An oxygen valve on a docked Progress cargo vehicle was kept open all Sunday night to keep the station above this critical level.
Foale and Kaleri have been able to temporarily patch the leaking hose. A replacement hose may be flown up to the station later in January on a Progress vehicle.
If the leak had not been found, mission managers were planning to confine the crew for five days to the Russian living quarters and perhaps one or two other modules as early as 14 January.
This would have enabled other station segments to be sealed off and checked. If the leak had persisted at its average level of 0.03 psi per day, the station contained enough oxygen and nitrogen on board to last for another six months.
The leak was made more worrisome because the main oxygen generator, which has been working only sporadically, failed again last week. Russian flight managers are designing a way to fix it this week with spare parts already on the station.
