The International Space Station’s two Russian astronauts ventured out on a spacewalk to prepare for next year’s arrival of a long-delayed lab.
Commander Sergey Ryzhikov and Sergey Kud-Sverchkov — dubbed Sergey 1 and Sergey 2 by flight controllers — left four Americans and one Japanese inside.
The space station population grew to seven late on Monday with the arrival of a SpaceX capsule, making the company’s second astronaut flight.
Mr Ryzhikov and Mr Kud-Sverchkov, on their first spacewalk, spent nearly two hours doing extra leak checks before exiting from an air lock.
The compartment has been at the space station since 2009 but it was being used for the first time by spacewalkers.
“Congratulations. You are out,” Russian Mission Control radioed from near Moscow.
Russia’s old spacewalking compartment will be removed and junked next year to make room for the research lab Nauka — Russian for “science”.
Several Russian-directed spacewalks will be required to deal with all this. The plan calls for attaching a cargo ship to the old Pirs module in order to guide it to a fiery re-entry.
The new 22-ton lab — stretching 43ft long — is so big that it will be launched from Kazakhstan by a powerful Proton rocket. Once at the orbiting outpost, it will double as an air lock and docking port.
The science lab’s launch — nearly a decade late because of a long string of repairs — is targeted for some time early next year.
Mr Ryzhikov and Mr Kud-Sverchkov arrived with an American last month on a Soyuz capsule. Like the newly arrived SpaceX crew, the Russian-launched astronauts will remain on board until spring.