Spacewalking to fix leak

The crew had noticed flakes of white ammonia, which runs in loops to cool the spacecraft's electricity supply system, floating away from an area outside the craft.

Mission managers spent Friday reviewing data on the leak and deciding whether to conduct a spacewalk to investigate, according to NASA.

"Tomorrow we send two crew out into the thermal vacuum wearing cloth-and-rubber pressure suits to repair ISS," station commander Chris Hadfield of Canada tweeted on Friday. "Extra study of procedures tonight."

The Americans Chris Cassidy and Tom Marshburn were on Saturday set to swap out a pump box on one of the eight solar panels that supply electricity to the station. Astronauts do not usually step out of the station on such short notice, but NASA quickly planned the repairs in order to try to fix the leak before all the ammonia escaped.

Station program manager Michael Suffredini described the situation as serious, but told a news conference that if the astronauts failed to fix the cooling system on Saturday, a later spacewalk would finish the job.

Suffredini said that space junk had likely hit a cooling tube, but he added that the area had a slow leak for many years. Two astronauts spacewalked to fix a similar ammonia leak in November.

According to NASA, the station has adequate power, and the six-man crew remains safe.

mkg/rc (AP, dpa)