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Spacewalkers to Make Critical Space Station Repairs

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Houston - Two astronauts are set to step outside the International Space Station (ISS) today and make a critical repair to aid future construction of the orbital laboratory.

Spacewalkers Piers Sellers and Michael Fossum, who spent more than seven hours working outside the ISS Saturday, will once again don their U.S.-built spacesuits to restore the station’s mobile crane to full operations. The spacewalk was set to begin at 8:13 a.m. EDT (1213 GMT).

The primary task for Sellers and Fossum, both mission specialists for NASA’s STS-121 shuttle mission aboard Discovery, is to replace a reel-like power and data cable system that was severed late last year due to a still-unexplained glitch.

Known as a Trailing Umbilical System (TUS) Reel Assembly, the system transfers electricity, data and video to the space station’s railcar-like Mobile Transporter. The transporter itself is a critical movable platform for shifting the ISS robotic arm or massive station components along the orbital laboratory’s main truss.

“It’s mobile now, but it’s only dependable on one string,” Sellers told reporters Sunday during a space-to-ground video link. “And when we’re done tomorrow, it will have two strings and therefore be more reliable.”

More: Space.com - Spacewalkers to Make Critical Space Station Repairs