Two International Space Station crew members on Wednesday successfully completed a spacewalk to install a new power switching unit, the US space agency NASA said.

American Sunita Williams and Japan's Akihiko Hoshide had to contend with a sticky bolt that prevented them from completing the installation in a previous spacewalk last week.

The ISS has four of the so-called Main Bus Switching Units, each weighing 100 kilos (220 pounds), which relay electricity from the station's solar array wings.

The malfunctioning power unit had deprived the space station of power from two of the eight solar wings, forcing crew members to switch off certain equipment on board.

Wednesday's nearly 6.5-hour spacewalk ended at 1734 GMT, NASA said.

"We are back in a very good shape in orbit," NASA's ISS program manager Mike Suffredini told a press conference at the Johnson Space Center in Houston.

It was the sixth spacewalk for Williams, a Navy captain who has now logged 44 hours as a spacewalker -- the most ever for a woman. The previous record was held by US astronaut Peggy Whitson.

On August 20, Russia's Gennady Padalka and Yury Malenchenko carried out a spacewalk of nearly six hours to install a shield to protect one of the ISS modules from micro-meteorites and space debris.

They also repositioned a telescopic crane, with a view towards the arrival in late 2013 of a new Russian laboratory module that will be attached to the ISS.

In addition to the spacewalks, the current ISS team is preparing for the arrival of four cargo vessels -- two from Russia, one from Europe and one from Japan.