The six-hour spacewalk involves upgrading the orbiting lab with new experiments to measure charged particle interactions and the effects of microbes on spacecraft materials

By Megan Gannon and SPACE.com

Russian cosmonauts Roman Romanenko (bottom) and Pavel Vinogradov flout outside the International Space Station on April 19, 2013, during the first spacewalk of their Expedition 35 mission. The two men will spend six hours upgrading the station' Image: NASA TV

Two Russian cosmonauts ventured outside the International Space Station Friday (April 19) to begin a six-hour spacewalk to upgrade the orbiting lab with new experiments.

Clad in their bulky Orlan spacesuits, veteran cosmonauts Pavel Vinogradov and Roman Romanenko began their spacewalk just after 10 a.m. EDT (1400 GMT) to install a space weather experiment to the space station's hull and prepare the outpost for the arrival of a robotic cargo ship later this year. You can watch the spacewalk live on SPACE.com, courtesy of NASA TV.

"It's dark outside," one of the cosmonauts said after they opened the hatch of the Pirs docking module, which doubles as a spacewalk airlock and spacecraft parking spot at the station. [Space Station's Expedition 35 Mission in Photos]

The spacewalk's first task is the installation of a new Russian experiment called Obstanovka, which will measure charged particles interact with a variety of materials kept outside of the space station. Obstanovka could offer scientists new insights about how space weather affects the ionosphere, an active region of the Earth's atmosphere, NASA officials explained in a spacewalk description.

Vinogradov and Romanenko also plan to retrieve a Biorisk canister, an experiment that measures the effects of bacteria and fungus on spacecraft materials, as well as part of a materials exposure experiment called Vinoslivost.

"All this is hard work," Romanenko said of the spacewalk in a NASA interview before launching to the station in December. "Also I'm supposed to collect information from other experiments that were installed outside the station."

Vinogradov and Romanenko are also expected to replace a faulty retro-reflector device needed to guide the upcoming arrival of the European Space Agency's Automated Transfer Vehicle 4 an unmanned cargo ship named "Albert Einstein." That robotic spacecraft will launch toward the space station in Juneand park itself at the orbiting laboratory's Russian-built Zvezda service module.

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Cosmonauts Take Spacewalk Outside Space Station