Heidemarie Stefanyshyn-Piper on the end of the robot arm as she moves a nitrogen tank assembly to the Space Shuttle Endeavour's cargo bay in this image from NASA TV November 18, 2008.

In this image from NASA TV, astronaut Stephen Bowen maneuvers down the cargo bay of the space shuttle Endeavour as he prepares to assist astronaut Heidemarie Stefanyshyn-Piper in placing an empty nitrogen tank into the shuttle's cargo bay, November 18, 2008.

Source: CCTV.com | 11-19-2008 10:35
A pair of space shuttle Endeavour's astronauts are on a mission outside the international space station, performing an unprecedented cleaning and lube job.

They're repairing the power system of the orbiting outpost so the space station's solar power panels can track the sun.

NASA astronauts Heidemarie Stefanyshyn-Piper and Stephen Bowen stepped outside the space station early on Tuesday afternoon.

It's the first of four spacewalks planned for the shuttle Endeavour's visit to the space station.

The astronauts are carrying grease guns, putty knives and oven-like mitts to try to remove metal grit from a gummed-up joint.

For over a year, the joint has been unable to automatically point solar wings toward the sun for maximum energy production.

The repair work is expected to take up much of their time during all four spacewalks.