Washington: Two NASA astronauts from the space shuttle Endeavour began a spacewalk Tuesday to replace a nitrogen tank on the International Space Station and begin repair of a joint on a key solar panel.

Heide Stefanyshyn-Pieper and Steve Bowen began the planned six-and-a-half hour walk at 18:09 GMT. The nitrogen tank will be installed with help for the station's robotic arm and will include the replacement of a device that moves the coolant through the station.

The astronauts will also begin inspecting, cleaning and lubricating the solar panel joint, which has been defective for more than a year. Most of the mission's four spacewalks will be devoted to getting the joint in order. On Tuesday's walk, astronauts will also remove thermal covers to inspect the Japanese Kibo module.

Endeavour arrived at the space station Sunday on its 15-day "home improvement" mission.