Endeavour spacewalkers Heidemarie Stefanyshyn-Piper and Shane Kimbrough have moved two rail carts across the International Space Station about a half-hour ahead of schedule. The spacewalk began at 12:58 p.m. and is expected to end around 7:30 p.m.
Kimbrough has moved on to his next task, which is greasing a sticky grappling mechanism at the end of the station's robotic arm, shown at left.
Stefanyshyn-Piper has returned to the rotary joint that is the main focus of the mission's first three spacewalks.
It's called one of two that rotate the station's solar wings so they can track the sun continuously and generate maximum power.
The joint - called a Solar Alpha Rotary Joint, or SARJ - on the station's starboard side has been damaged for about a year and unable to rotate properly.
The spacewalkers are engaged in a short-term fix to clean off metal debris shaved off by trundle bearings and grease the gear ring, hopefully enabling it to turn with less vibration and power.
Stefanyshyn-Piper and Steve Bowen removed two bearing assemblies on Tuesday. Today, Stefanyshyn-Piper and Kimbrough will remove and replace four more sets of bearing assemblies. The joint was rotated in between spacewalks to move new sets of bearings into position where the spacewalkers can reach them. Eventually, 11 of 12 sets will be replaced. A 12th set was removed on an earlier mission.
The graphic above shows in blue the areas being worked on today, and in red the areas that were covered Tuesday. Click on the graphic or any of the pictures to enlarge them.
The image at left, from Kimbrough's helmet camera, shows the robotic arm snares he is working on. 
Here, you can see the grease gun Kimbrough will use to lubricate the snares.
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