Two U.S. astronauts are on another spacewalk to continue construction of the international space station. Their work combines the skills of plumbers, electricians, mechanics, and television technicians.

Visiting U.S. space shuttle Atlantis crewmen David Wolf and Piers Sellers are on the second of three spacewalks needed to connect a newly-installed section of the station's growing backbone to the first.

The backbone is an aluminum girder that will eventually extend more than 100 meters to support cooling, power, and data relay equipment for future research laboratories.

On this outing, the two astronauts are installing an external television camera on the existing U.S. laboratory, working on coolant tube connections between the two girder sections, and releasing brakes on a small rail flatcar that will roll along the girder during future construction activities.

One more spacewalk is scheduled for Monday to continue the truss work before Atlantis departs the station on Wednesday.