False alarm on International Space Station causes panic

Astronauts returned to the US portion of the International Space Station on Wednesday after an earlier false alarm triggered an evacuation of a section of the orbiting laboratory.

All six crew members moved to the station's Russian section early today after a warning suggested trouble with a coolant-pressure system on the American side that could have been a dangerous ammonia leak, the National Aeronautics and Space Administration said in a statement on its website. The agency later said an error message in the computer relay system may have triggered the alarm.

The crew members were never in danger, NASA said. Though no ammonia was detected, the astronauts donned protective masks when re-entering the US segment.

The precautions were taken because an ammonia leak in the cabin could lead to costly mission complications or loss of life, said Leroy Chiao, a former astronaut who served as commander of the space station for six months until early 2005. An internal ammonia leak has not happened on the station, but Chiao called such an occurrence a ''nightmare scenario.''

After the alarm went off, crew members sealed off the affected section and cut power to non-essential equipment, NASA said.

The crew includes two Americans, Commander Barry Wilmore and flight engineer Terry Virts. Following the evacuation, European Space Agency astronaut Samantha Cristoforetti, who has been aboard the station since November, said on Twitter that ''we're all safe & doing well in the Russian segment.'' The other three astronauts manning the station are Russians.

The scare may result in minor delays to some research activities, including an experiment involving fruit flies, but no research was jeopardized, NASA said.

While the station has 388 cubic metres) of habitable space - about the same as a six-bedroom house - fitting everyone into the Russian segment was tight.

While the sensors on the space station are generally reliable, they occasionally give false readings, Chiao said.