CAPE CANAVERAL, Fla. -- Mission controllers suspect a leaky hose in the international space station's U.S.-built laboratory module may be the source of a slow drop in air pressure over the past three weeks, but they are still trying to confirm it, NASA said Monday.
The space agency also said the station's next scheduled commander has been replaced because of an undisclosed medical issue.
Extra oxygen was pumped into the space station during the weekend to replenish the dwindling air supply for astronaut Michael Foale and cosmonaut Alexander Kaleri. On Monday, the pressure seemed to be stabilized at 14 pounds per square inch, Mission Control said.
The leak never endangered the crew or space station operations, NASA said. The station's normal air pressure is 14.7 pounds per square inch.
NASA said astronaut William McArthur will not replace Foale in the spring as the station's skipper because of a temporary medical problem that disqualifies him for a six-month spaceflight. Officials refused to elaborate, citing medical privacy.
McArthur will be replaced by backup Leroy Chiao, also a space veteran.
In 2002, another NASA astronaut had to be bumped from a space station mission because of concern over the amount of radiation to which he'd be exposed during such a long flight.
Foale and Kaleri discovered the leaky hose Sunday using a handheld ultrasound leak detector to track the hiss of the escaping air. The hose is used to vent air overboard from between two panes of the high-quality optical window in the American-built lab to prevent a condensation buildup.
Foale removed the hose and capped off both ends of its valve fittings. If that is confirmed as the location of the leak a spare hose will be sent up on a Russian spacecraft.
Earlier Monday, Russian space officials had identified a malfunctioning pressure relief valve as the source of the leak.
Flight controllers debated Monday whether to go ahead with sealing off the U.S. and Russian sides of the orbiting complex to make sure nothing else is leaking. That would take place no earlier than Wednesday, NASA said.
The hatches to a few station compartments were closed one at a time during the weekend but no leaks were found.
The space station is limited to two crew members because of the grounding of the U.S. shuttle fleet after the Columbia accident. Chiao will be launched aboard a Russian rocket in April with cosmonaut Valery Tokarev.
On the Net:
NASA Space Station: http://spaceflight.nasa.gov/station/