Once ammonia coolant is flowing through the hoses, Tranquility will begin surging with power. Its systems cannot be turned on unless there is a way to get rid of the heat generated by the equipment inside.
It was unwieldy work because of the extra-long hoses and potentially hazardous because of the ammonia coolant.
In fact, frozen bits of ammonia shot out at Patrick as he undid a connection. He said the ammonia was solid by the time it bounced off his visor and right glove, and he assured his colleagues there was no residue on him.
"It was about the kind of quantity of stuff that you would expect if you didn't empty the straw at the end of your drink bag," Patrick reported.
"Yeah -- if you were drinking ammonia," astronaut Stephen Robinson said from inside. Patrick had a good laugh.
Mission Control said slight leakage was expected. As a precaution, the spacewalkers were instructed to check their suits at the end of the plumbing job.
The hoses stretched 14 feet to 18 feet. They were fashioned right before space shuttle Endeavour's trip to the space station. The original ammonia lines failed tests, and so engineers had to put together replacement hoses from shorter spares that were welded together.
The $400 million-plus Tranquility and lookout -- supplied by the European Space Agency -- will hold life-support systems as well as exercise equipment and a toilet.
The domed lookout is essentially an enormous bay window that will provide breathtaking views of Earth. Its seven windows includes the largest ever flown in space: a round one 31 inches across.
While preparing the observation deck for its planned move to another side of Tranquility, the astronauts could not put on an insulating cover at the hatch. It simply did not fit; something interfered with the lock-down bars.
Late Saturday, the space station's commander, Jeffrey Williams, reported that bolts seemed to be causing the interference. He removed all eight bolts, saying the clearance would be tight but that the cover likely would fit.
The cover is needed to protect a seal and docking mechanisms from getting too cold when that port is unoccupied.
Mission Control had some good news for the six shuttle astronauts before the spacewalk got under way: They will get to spend an extra day at the orbiting outpost.
Mission managers on Saturday added a 14th day to the mission to give the crew time to move water-recycling equipment into Tranquility. NASA wanted to see if repairs to the broken urine-processing machine worked before moving the equipment. They apparently did.
Endeavour is now scheduled to return to Earth on Feb. 21.