Because the station's emergency system was activated, the ventilation system was shut down, but ground operations reactivated it a short time later. Astronauts used a charcoal air-scrubbing device to remove the offensive smell and Williams said the odor "decreased significantly."

The potassium hydroxide, a corrosive that can cause serious burns and can be harmful if inhaled, was cleaned up with towels and wrapped up in two rubber bags, Suffredini said.

Potassium hydroxide can be used to power batteries and is also known as potash lye.

The Elektron system has given the space station headaches before. It had operated on-and-off for months before breaking down last spring. In June, the crew tried to reactivate it, with mixed results, after replacing a hydrogen vent valve outside during a spacewalk.

The failure of the Elektron, which looks like a water heater, had no impact on operations at the space station.

The international space station was in the middle of a revolving door of visitors. Space shuttle Atlantis' six astronauts departed on Sunday and a Russian Soyuz vehicle carrying two new station crew members and space tourist Anousheh Ansari were expected to arrive on Wednesday.

Early Monday, Atlantis astronauts attached a boom to the shuttle's robotic arm and inspected for damage to the shuttle's wings and nose. This is part of the post-Columbia accident routine for shuttles, in which astronauts look for the type of heat shield cuts and tears that caused the fatal shuttle accident in 2003.

The inspection was conducted by pilot Chris Ferguson and astronauts Dan Burbank and Steve MacLean while the shuttle stayed dozens of miles away from the station in the same relative orbit. If the astronauts find the type of damage that could cause a deadly accident, the shuttle can return to the station. Earlier inspections showed the heat shield was in good condition.

At the same time, astronauts examined and tried to fix what may be a minor leaky valve used for dumping water overboard.

Mission Control praised Atlantis for completing its main mission of adding a 17 1/2-ton addition, including a pair of 115-foot-long solar wings, to the space station.

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