Two NASA astronauts made space history on October 18, completing the first spacewalk by an all-women team when they stepped outside the International Space Station.

Christina Koch and Jessica Meir accomplished the much-anticipated milestone for NASA during a relatively routine mission to swap faulty batteries on the station's exterior.

A first attempt at an all-female spacewalk in March was called off because one of the astronauts’ medium-sized spacesuits was not configured and ready for the journey.

Koch, an electrical engineer, was leading Meir, who holds a doctorate in marine biology and is making her first ever spacewalk.

The two were working to replace a faulty battery charge/discharge unit, known as a BCDU. The station relies on solar power but is out of direct sunlight for much of its orbit and therefore needs batteries, and the BCDUs regulate the amount of charge that goes into them.

The current task is part of a wider mission of replacing aging nickel-hydrogen batteries with higher capacity lithium-ion units.

This was Koch’s fourth spacewalk and Meir’s first. Both women, selected as astronaut candidates in 2013, are on their first trip to work and live aboard the space station. Meir is the 15th woman to spacewalk.

Koch is scheduled set to complete the longest single space flight by a woman by remaining in orbit aboard the station until February 2020. 

The US sent its first female astronaut into space in 1983, when Sally Ride took part in the seventh Space Shuttle mission, and has now had more women astronauts than any other country. But the first woman in space was Soviet cosmonaut Valentina Tereshkova in 1963, followed by compatriot Svetlana Savitskaya in 1982, who was also the first woman spacewalker two years later.

The spacewalk comes as NASA plans to return to the Moon by 2024 under the Artemis mission, named for the twin sister of Apollo in Greek mythology. The mission will see the first woman to set foot on the lunar surface, possibly as part of an all-women team.