Two Russian cosmonauts floated outside the International Space Station on Friday to set up power and ethernet cables for a new research laboratory scheduled to arrive in December.

Flight engineers Fyodor Yurchikhin and Alexander Misurkin opened the hatch on the station's Pirs airlock at 10:36 am EDT (1436 GMT) to kick off a 7-hour, 29-minute spacewalk, the longest ever by Russian cosmonauts.

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The spacewalk eclipsed by 13 minutes the Russians' previous record set in July 2000 outside the Mir space station. The longest spacewalk overall was an 8-hour, 56-minute outing in 2001 by two NASA astronauts working outside the International Space Station.

Yurchikhin, who was making his seventh spacewalk, and Misurkin, on his second, spent most of their time routing two power cables and an ethernet line for a new Russian multipurpose laboratory called Nauka.

"There's a lot of intricate and delicate stringing (of the cables) through handrails and hook points," NASA mission commentator Rob Navias said during a televised broadcast of the spacewalk.

The outing is the third of six spacewalks Russia plans to conduct this year.

NASA meanwhile is still investigating the cause of a spacesuit helmet leak that forced two other crew members at the space station to abort a spacewalk on July 16.

Russia's Orlan spacesuits are different from NASA's but "due diligence was paid in preparation for this spacewalk," Navias said.

"Everything was in good shape," he added.

In addition to rigging cables between the Russian Zarya and Poisk modules, Yurchikhin and Misurkin attached a panel of experiments on a handrail on Poisk that will remain outside to expose sample materials to the space environment.

The cosmonauts are scheduled for another spacewalk on August 22 to install a swiveling platform for a telescope.

Russia's Nauka module, which will serve as research lab, docking port and airlock, will replace the Pirs docking compartment, which will be detached from the space station and flown into the atmosphere, where it will be incinerated.