Astronauts repair space station

Spacewalking astronauts installed a new ammonia pump at the International Space Station yesterday, accomplishing the urgent cooling-system repairs after more than two weeks of impaired operations.

Making his third spacewalk in just 10 days, Douglas Wheelock slid the bathtub-size pump into place then bolted it down as Tracy Caldwell Dyson hooked up power cables.

An initial test proved successful. "Sweet," Mr Wheelock exclaimed.

The astronauts then connected all the ammonia fluid lines. To everyone's relief, the work went smoothly, with no apparent leakage of the toxic substance. During the first spacewalk, ammonia streamed out and forced Nasa to add an extra outing to get the job done.

"We did not see any ammonia come out today, amazingly," Mission Control radioed.

Mr Wheelock proudly showed off the checklist on his arm cuff to the TV cameras. Printed in black ink were the words, "Game over!!"

Flight controllers still have more tests to conduct. If everything goes well, Nasa expects to have the space station's disabled cooling loop back in action by Thursday.

The orbiting lab has been operating on only half its normal cooling capability ever since a crucial ammonia coolant pump failed on 31 July. Science research was halted and unnecessary equipment turned off to avoid overtaxing the single functioning cooling line.