NASA astronauts Jessica Meir and Christina Koch preparing on the International Space Station for the first all-female spacewalk. Photo: NASA

On the first ever all-female spacewalk, NASA astronauts Christina Koch and Jessica Meir ventured outside the International Space Station (ISS) today at 7:38 a.m. EDT, to replace faulty equipment on the station’s exterior.

The astronauts replaced a faulty battery charge/discharge unit (BCDU) that failed to activate following the Oct. 11 installation of new lithium-ion batteries on the space station’s exterior structure. The BCDUs regulate the amount of charge put into the batteries that collect energy from the station’s solar arrays to power station systems during periods when the station orbits during nighttime passes around Earth. Though the BCDU failure has not impacted station operations or crew safety, it does prevent the new batteries from providing increased station power.

The spacewalk was the 221st in support of station assembly, maintenance, and upgrades and the eighth outside the station this year. This was Koch’s fourth spacewalk and Meir’s first. It is the first spaceflight for both women, who were selected as astronaut candidates in 2013 as part of the first class, of which 50 percent were women. Meir will be the 15th woman to spacewalk, and the 14th U.S. woman. It will be the 43rd spacewalk to include a woman. Women have been performing spacewalks since 1984, when Russian cosmonaut Svetlana Savitskaya spacewalked in July and NASA astronaut Kathryn Sullivan conducted a spacewalked in October.