Spacewalk behind due to stuck ammonia coolant line

Unable to disconnect an ammonia fluid line from an International Space Station coolant system pump, two NASA astronauts have moved on to a backup plan as they head into the tail end of a planned seven-hour spacewalk.

Doug Wheelock and Tracy Caldwell Dyson are now trying to connect two other lines to a jumper box after wrestling with the ammonia line for about an hour.

It's hoped that move will help relieve pressure that might have kept a quick disconnect valve from releasing the 1.5-inch diameter ammonia line, one of three attached to the pump along with a fourth, smaller coolant line.

The planned seven-hour spacewalk is more than five hours old, so it's not yet clear how much more the spacewalkers can accomplish today.

NASA had hoped they could remove the failed pump module and put a spare in its place, but the 780-pound module can't be removed until all four fluid coolant lines are released.

The stuck ammonia line leaked slightly, so the astronauts may need to take some time to make sure their spacesuits are uncontaminated before returning inside the Quest airlock.