Florida ? A pair of spacewalking astronauts floated back outside Saturday night to hook up plumbing on the newest room of the International Space Station and bring it alive with power.

It was the second excursion in three days for Robert Behnken and Nicholas Patrick. They have one more spacewalk to finish installing the Tranquility room and its attached observation deck, the last major building blocks of the 11-year-old space station. Endeavour carried up the pieces last week.

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.