Two U.S. astronauts are busy assembling a robot outside the International Space Station in the second of five scheduled spacewalks of space shuttle Endeavor's mission.

Spacewalkers Richard Linnehan and Mike Foreman stepped into the void of space at 7:49 p.m. EDT (2349GMT) on Saturday, and the spacewalk may last until 3:00 a.m. on Sunday (0700GMT) reported NASA's mission control center on the ground.

The duo are putting together pieces of a robot named Dextre, which was delivered to the orbital outpost by Endeavor on Wednesday.

During Thursday's first spacewalk, these astronauts attached two "hands" to the arms of Dextre. Linnehan and Foreman will put the arms to its shoulders during tonight's excursion, said the mission control center.

A third spacewalk, scheduled for Monday night, will facilitate Dextre with a tool holster.

Dextre is the final element of the station's Mobile Servicing System. It was designed and built by the Canadian Space Agency. Once fully assembled, it will assist the spacewalking astronauts outside the station in the future.

Throughout Saturday, the station and shuttle crew continued outfitting the Japanese Logistics Module, the first component of Japan's orbital laboratory Kibo.

(Xinhua News Agency March 16, 2008)