Extra spacewalk likely as repairs fall short

NASA expects to conduct an extra, third spacewalk outside the International Space Station after efforts Saturday to repair a failed cooling system on the orbiter fell short, the agency said.

"I really think we're going to end up with three EVAs," or extra vehicular activities, ISS manager Michael Suffredini said after completion of a first spacewalk in which US astronauts were unable to unhook and remove the busted module that has caused the cooling problem.

A second spacewalk has already been scheduled for Wednesday, but NASA said it was becoming clear that a third walk was now needed.

"It would take a lot of good luck and somebody coming up with a really short tweak to the EVA for us to get to the point where we can start that (new) ammonia pump" after the second spacewalk, Suffredini told a briefing shown on NASA's website.

"We're going to end up being in this condition, this risk posture, a few more days than originally planned," he said.

The news is a setback for the US space agency. Astronauts Doug Wheelock and Tracy Caldwell Dyson had just completed the longest-ever spacewalk outside the ISS, eight hours and three minutes, but failed to wrest the faulty pump module from the outside of the station's S1 truss.

"We did our best to get it disconnected, but it didn't apparently want to," spacewalk flight director Courtenay McMillan said.

NASA encountered trouble with the four valves and their quick disconnect, or QD, mechanisms the astronauts needed to use in order to get the module completely unhooked and removed.

NASA described the QDs as "sensitive systems" designed to feed ammonia through the valves at high pressure.

Astronauts noticed ammonia had built up around one valve, and it started leaking ammonia when opened. After a period of troubleshooting NASA decided not to continue unhooking them.

Experts will meet at Mission Control in Houston, Texas on Sunday to map out the next steps, NASA said.

The agency will need "probably a couple more EVAs to get the job done," McMillan said.

Officials did not suggest that the six-person crew of the ISS was in any immediate danger, but Suffredini said NASA was "looking at every possible option" to ensure the rapid resolution to what has become a nagging problem on board the orbiting station.

"We will get through this problem," he said.

"The challenge is to get through this problem before the next problem hits the other cooling system."

The pump which failed last weekend is one of two that circulate ammonia coolant throughout the orbiting ISS. NASA has said it considers a failure of the second cooling unit highly unlikely.