Two female astronauts are making history as they conduct the first all-female spacewalk. NASA astronauts Christina Koch and Jessica Meir are outside the International Space Station this morning. You can see them in action in the video below:

Originally scheduled for Oct. 21, NASA pushed the spacewalk up to today so the astronauts could upgrade the station's power system. The pair are fixing the station’s battery charge/discharge unit (BCDU), a process that's expected to take more than five hours, Reuters reports.

Koch was originally scheduled to conduct a spacewalk with her then-crewmate, Anne McClain, on March 29, following another spacewalk featuring McClain and NASA astronaut Nick Hague on March 22. However, mission managers decided to change assignments, NASA explained, "due in part to spacesuit availability on the station."

McClain realized her best fit was a medium-sized hard upper torso — "essentially the shirt of the spacesuit," according to NASA. But there was only one available in time for the spacewalk, so Koch wore it and Hague filled in for McClain.

"It is more efficient to swap spacewalkers than to reconfigure the elements of the spacesuit," NASA spokeswoman Stephanie Schierholz told NBC News, noting the fit of a spacesuit can affect an astronaut's ability to maneuver and perform tasks.

But now the suits and the astronauts are ready. Another medium size suit was launched to the ISS earlier this year, according to Kirk Shireman, NASA’s program manager for the ISS, the Verge reports.

"We don't do it for a specific crew member," Shireman said during a press conference in early October. "Actually, what we do is we look over the next two years, and look at all the crew members who are [spacewalk] certified, and say, ‘OK, what’s the sweet spot?’” Shireman pointed out that over the next couple of years, a lot of "medium suit people" will be heading to the ISS.

Koch talked about how their accomplishments are viewed in terms of being female astronauts.

In July 1984, cosmonaut Svetlana Savitskaya became the first woman to walk in space. Thirty-five years after that historic occasion, two women will conduct the first all-female spacewalk.

Spacewalks are conducted for a range of reasons, from performing experiments outside of the International Space Station to testing and repairing equipment.

Editor's note: This story has been updated with new information since it was originally published in March 2019.

NASA's all-female spacewalk is happening
NASA astronauts make history with an all-female spacewalk — now that the spacesuit problem is resolved.