Foale and Kalery had managed to complete much of the planned work when the temperature control in Kalery's suit went out of order, forcing the cosmonaut to return to the station, said the head of Russian mission control center's press service Valery Lyndin.

"Their mood is normal. They have done almost everything that was scheduled," Lyndin told AFP.

Neither astronaut was in imminent danger, but the pair had to interrupt the spacewalk due to regulations which do not allow a single astronaut to work in space without backup, Lyndin explained.

Foale and Kalery, who opened the hatch at 00:17 Moscow timeThursday), managed to attach two human-imitating mannequins, the European-made "Mister Rando" and the Russian-made "Matryoshka-R" to the ISS's Zvezda module.

The mannequins would allow scientists "to collect information on the doses of radiation humans are exposed to over a long-term space flight," medical experts said earlier.

The two astronauts also managed to disconnect some of the old panels for Russian and Japanese experiments held on board the ISS, but failed to move in place a laser-based homing system for the European Space Agency (ESA)'s cargo craft, due to be sent to the ISS next year.

This was the first spacewalk held since the US space shuttle Columbia disaster in February 2003 which claimed the lives of seven astronauts and left Russia the sole supplier of the station.

SPACE.WIRE