After an amazing ride above the space station, spacewalker Ron Garan has installed a swapped nitrogen tank, while Mike Fossum climbs out to inspect the port solar alpha rotary joint.
Holding first an empty tank then a full one, Garan rode the space station robot arm while holding the 528-pound tanks. The former F-16 pilot has attached the four bolts that hold the tank and later will attach fluid connectors.
Fossum will sample dust on the joint by collecting it with tape. Metal has flaked from the 10-foot race ring on the opposite joint. NASA managers hope the sample will help them avoid a more serious malfunction in the joint that turns the massive solar wings to face the sun.
Garan and Fossum are performing today's third and final spacewalk of STS-124. Nitrogen is used to pressurize the space station's cooling system.
The spacewalk officially began at 9:55 a.m. ET, when the pair switched their spacesuits to battery power, which they did about a half hour before the scheduled start time. During the previous spacewalk, Fossum and Garan started early, accomplished all tasks and performed extra tasks.
The pair will remove and replace the nitrogen tank assembly, remove some thermal covers, re-install a port truss camera, and Fossum will grab a sample of material from the port solar alpha rotary joint. Fossum and Garan also will return to the Kibo module robot arm to remove another set of launch locks and allow the arm to be put in service.
The 6.5-hour spacewalk will be the 112th in support of space station construction.
On Saturday, Discovery crewmembers Akihiko Hoshide and Karen Nyberg moved Kibo's robotic arm for the first time, slightly maneuvering two of its six joints.
Full deployment of the 33-foot arm will be done after Discovery leaves the station next week. However, it won't be used for any actual work until after the launch into orbit next year of the lab's third and final section — a "porch" for exterior experiments — and a second, smaller robotic arm.
Japanese Prime Minister Yasuo Fukuda spoke to Hoshide and Discovery commander Mark Kelly and congratulated them on Kibo's successful installation.
Kibo, Japanese for hope, was delivered by the shuttle and installed on the space station last week.
Also Saturday, several thermal protective panels on Discovery's right wing that the astronauts had photographed because of some slight pulses in their embedded sensors were given the "all clear," said flight director Annette Hasbrook.
The wing sensors are one of NASA's many safety measures put in place after Columbia was destroyed during re-entry in 2003 as a result of a gashed wing.