Two shuttle Endeavour astronauts finished the longest of their planned spacewalks outside the orbiting International Space Station on Saturday, a nearly seven-hour effort aimed at cleaning and repairing a contaminated joint on the station's solar power array.
Heidemarie Stefanyshyn-Piper and Stephen Bowen returned to the station's Quest airlock at 7:58 p.m. EST/0058 GMT after spending six hours and 57 minutes working in the vacuum of space as the station sailed about 225 miles (362 km) over Earth.
Stefanyshyn-Piper and Bowen worked together inside a 10-foot-(3-meter-)wide rotary joint, one of two on the station that pivot the station's sprawling solar wings so they can face the sun for power.
One of the joints is contaminated with metal filings, which engineers believe stemmed from a lubrication problem. A total of four spacewalks are planned for the 11-day mission.
The repair involves greasing the joint's metal ring so the debris can be collected and scraped off.
NASA planned for both astronauts to use grease guns, but a set of tools, worth about $100,000, accidentally floated off into space during the mission's first spacewalk on Tuesday.
The astronauts shared a grease gun during that outing and then revised their cleanup procedures to use grease-impregnated wipes for later spacewalks.
As a backup, NASA had the astronauts modify one of two caulking guns, flying as part of an emergency shuttle heat shield repair kit, so that it could dispense grease.
After earlier spacewalk glitches, Saturday's work went off without a hitch, NASA officials said.
"The crew executed as perfect (a mission) as I've ever seen," said John Ray, lead spacewalk officer for the mission. "They were right on top of their game."
While astronauts worked outside the station, engineers on the ground puzzled over problems with a new water recycling system that was installed in the outpost's Destiny laboratory earlier this week. The device is designed to purify urine and other wastewater so that it can be used by the crew for drinking and for producing oxygen.
NASA needs to have the system working before the station's crew size can be expanded from three people to six next year.
A centrifuge in part of the machine that distills urine has shut down repeatedly since its initial activation on Thursday. NASA hopes to resolve the problem in time for shuttle Endeavour to bring back samples of the purified water for analysis on Earth.
The shuttle is scheduled to depart the station on Thursday and return home to the Kennedy Space Center in Florida next Saturday.