Toxic leak: space station repair fails

A toxic ammonia leak and a jammed fitting have foiled plans to fix a cooling pump on the International Space Station, forcing astronauts to delay the repairs until Wednesday at the earliest, reports NASA.

On Saturday, Expedition 24 Flight Engineers Doug Wheelock and Tracy Caldwell Dyson suffered setbacks that stretched their space walk to 8 hours 3 minutes - the longest in space station history and the sixth longest ever undertaken, according to NASA.

The astronauts began their excursion outside the International Space Station at 0719 EDT (1119 GMT) as the outpost flew 220 miles (354 km) above Earth.

They planned to remove a broken ammonia coolant pump and install a replacement, which involved disconnecting four ammonia hoses and five electrical cables from the pump on the station's truss.

Problems arose about 4 hours into the spacewalk when one of the hoses wouldn't come loose. Colonel Wheelock managed initially to open the "quick-disconnect" fitting mechanism on the hose by hitting it with a hammer, but then reported a clearly visible ammonia leak.

"I see little sparklets of ammonia coming from the line," he said. The astronauts compared the crystals of frozen ammonia coolant to tiny snowflakes.

Colonel Wheelock re-tightened the fitting before returning to the airlock, where he had to delay entering the station so any toxic ammonia on his suit had time to evaporate.

Michael T. Suffredini, manager of the space station program at the Johnson Space Center in Houston, said he was disappointed by the setbacks.

He said that these ammonia quick-disconnect fittings are complicated. "It's very high-pressure ammonia, you have to try to be able to disconnect and reconnect on a regular basis."

The space station is now running on a single cooling system. "The challenge is to get through this problem before the next problem hits the other system," Suffredini stated.