Astronauts Sunita Williams and Akihiko Hoshide began a spacewalk on Wednesday in another attempt to install a power unit on the International Space Station.

The operation was broadcast live on NASA TV.

Their main task was to complete the installation of a spare power unit on the station's truss, which caused problems during an August 30 spacewalk.

Williams and Hoshide built some improvised tools to assist with their installation tasks, NASA said.

The spacewalk was scheduled to last 6.5 hours and included other tasks postponed from last week's excursion if the MBSU installation task is completed on time.

Last time NASA Flight Engineer Williams and Japan Aerospace Exploration Agency Flight Engineer Hoshide spent 8 hours and 17 minutes in space, but failed to install a new Main Bus Switching Unit (MBSU) on the station's s-zero truss as they had difficulties driving the bolts to secure the equipment.

The MBSU is a heavy component that is used to relay power from the station's solar arrays to its systems.

Williams and Hoshide's previous spacewalk was the third longest in history. The longest of 8 hours and 56 minutes was carried out by U.S. astronauts Susan Helms and James Voss in 2001.