Crew members on board when the leak was discovered on Aug. 30 quickly located and sealed a tiny hole in the Russian Soyuz spacecraft attached to the space station. The leak created a slight loss of pressure, and space officials said the station has remained safe to operate.
Russian cosmonauts Oleg Kononenko and Sergei Prokopyev embarked at 1559GMT (10:59 a.m. EST) for what it is expected to be a six-hour spacewalk to inspect the Soyuz's outer surface. They plan to uncover the thermal insulation covering the patched hole and take samples for experts to study.
Kononenko, who arrived at the station earlier this month with NASA astronaut Anne McClain and David Saint-Jacques of the Canadian Space Agency, said in a pre-flight interview that the spacewalk would be strenuous.
"It's going to be challenging both physically and technically," he said.
Roscosmos chief Dmitry Rogozin said in September that the hole could have been drilled during manufacturing or in space. He didn't say if he suspected any crew members of creating it on purpose, but his comment caused some bewilderment.
At 10am ET: Join us for live coverage of today's #spacewalk at the @Space_Station, set to begin at 11am ET and last around six hours. Two cosmonauts will inspect the #Soyuz crew ship that will return three other crew back to Earth Dec. 19. Details: https://t.co/a9eot68ImS pic.twitter.com/hOzWQhf7Au— NASA (@NASA) December 11, 2018
Rogozin has since backpedaled on his statement, blaming the media for twisting his words.
He said recently that an official Russian probe is ongoing and crew members who are set to return to Earth on Dec. 20 would bring back samples collected during Tuesday's spacewalk.
Rogozin added that Roscosmos would discuss the findings from the investigation with NASA and other space station partners.
A version of this story was corrected to say the spacewalk was set for Tuesday, not Wednesday.