Two veteran cosmonauts have floated outside the International Space Station to prepare the orbital outpost for a new module and protect its living quarters against debris impacts.

Dressed in spacesuits, station commander Gennady Padalka and flight engineer Yuri Malenchenko opened the hatch on the station's airlock to begin the six hour spacewalk.

The pair plan to move a hand-operated crane, called Strela-2, from the outside of the Pirs docking module to Zarya, the cornerstone of the station.

The expandable 46-foot boom will be needed next year to install a new Russia module to the station, a project of 15 countries.