Astronauts finish space walk

Two astronauts returned safely inside the International Space Station (ISS) on Saturday, following efforts to replace a part on a system that was believed to have been leaking ammonia coolant. Thus far, their work seems to have paid off.

"No evidence of any ammonia leakage whatsoever. We have an airtight system - at the moment," Mission Control reported on Saturday.

NASA said that the two ISS engineers, Chris Cassidy and Tom Marshburn, were back inside after their five-and-a-half-hour spacewalk to replace a 266-pound (121-kilogram) controller box.

The spacewalk was quickly arranged after astronauts noticed on Thursday that ammonia was floating outside the station.

Following Saturday's repairs, the new pump appeared to be working with no signs of a leak. NASA will continue to monitor the situation to see if the repair was a complete success.

Quick preparations

Flight controllers back in Houston, Texas, worked hard to prepare for the spacewalk, readying for it in just 48 hours. It was the third spacewalk for both Cassidy and Marshburn, both of whom were trained for such emergencies before leaving Earth.

The only worrying part of Saturday's endeavor was that the astronauts were unable to identify the source of the problem. They had suspected the ammonia pump was the culprit and set out to replace it, but they found nothing amiss on or around the old pump.

"All the pipes look shiny clean, no crud," Cassidy said as he inspected the old pump. "I can't give you any good data other than nominal, unfortunately. No smoking guns."

Despite finding nothing wrong, experts decided they had little to lose by replacing the part. Cassidy and Marshburn worked over several hours to replace the suspect pump.

NASA will continue to monitor the success of Saturday's repair.

No real danger

This area of the ISS has proven prone to leaks in the past. A similar leak, for example, occurred just last November.

The ammonia is used to cool the space station's electronic equipment.

During this week's leak, seven of the eight channels continued to operate normally, so the astronauts were never really in any danger of the electrical system being affected.

The 100-billion-dollar (77-million-euro) ISS flies about 250 miles (400 km) above Earth and is used as a research laboratory for scientific experiments and technology development.

tm/slk (AP, dpa, Reuters)