On Friday, two astronauts did a little house work to keep the lights on at the International Space Station, some 155 miles above the Earth. Shane Kimbrough and Peggy Whitson ventured out of the warm and fuzzy station indoors and into the cold vacuum of space to conduct a 6.5-hour spacewalk to replace a set of batteries which store power amassed by the station’s solar power arrays. This is the third spacewalk (NASA’s preferred term is ‘extravehicular activity,’ or EVA) for Kimbrough, and the seventh for Whitson. The latter, at 56, is the oldest female astronaut to fly into space. Friday’s EVA makes her the oldest woman ever to go on a spacewalk.

“All our power here on board the space station is collected by solar arrays,” Whitson said in a NASA interview. “But of course, as we’re going around the Earth 16 times in a day, half of that time the Earth is between us and the sun and so we have to have a way to store our power. Our batteries have been there in place many, many years and it’s time for us to replace (them) with new batteries outside.”

The station is fitted with four huge sets of solar arrays that work to power the entire $1 billion dollar hunk of metal orbiting the Earth. Each array has 12 nickel-hydrogen batteries. This operation calls for replacing 12 of those batteries with six smaller but more powerful lithium-ion power packs, delivered to the ISS last month.

kimbrough whitson nasa spacewalk
Kimbrough and Whitson are going to be in space for a loooooong time.

Houston flight controllers remotely worked over New Year’s to install three of the lithium-ion batteries and remove four of the older batteries. Friday’s spacewalk will make more progress, and a second EVA scheduled for January 13 (to feature Kimbrough and ESA astronaut Thomas Pesquet) will finish off the job.

NASA is currently airing live footage of the EVA on their website and on NASA TV, and the International Space Station’s Facebook page is streaming it live as well.

Photos via NASA TV