Washington  - Two NASA astronauts from the space shuttle Endeavour completed a spacewalk on 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 six-and-a-half hour walk at 1809 GMT. Ground controllers declared the spacewalk completed within the alloted time.

The nitrogen tank was installed with help from the station's robotic arm, and the device that moves coolant through the station was replaced.

The astronauts began 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.

The astronauts also removed thermal covers to inspect the Japanese Kibo module.

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