Updated at 3:30 p.m. ET
About 35 years after the first American woman walked in space, NASA set another milestone on Friday, as astronauts Christina Koch and Jessica Meir conducted the first all-female spacewalk.
Koch, an engineer, and Meir, a biologist, suited up and entered the "crew lock" that serves as the International Space Station's doorway into space. They switched on the battery power in their suits at 7:38 a.m. ET, signaling the official start of the spacewalk.
The outer hatch began opening as controllers on the ground finished ensuring the astronauts' suits were ready, including visors that are required because of the sunlight hitting the station. Then, Koch received the word.
"Christina, you may egress the airlock," said NASA's Stephanie Wilson, the spacewalk's coordinator at Mission Control Center in Houston.
"Copy," Koch answered.
In what the space agency billed as "HERstory," the four men aboard the International Space Station remained inside the orbital outpost, as Koch and Meir stepped outside to replace a broken battery charger.
The pair's spacewalk went nearly two hours longer than their planned 5.5-hour excursion. After finishing replacing the battery component in about three hours, they moved on to other tasks, such as installing a stanchion to support a new research platform that will be used on the outer surface of the station next year. All the while, they worked to keep their safety tethers from becoming twisted as they moved around.
More than six hours after the astronauts exited the space station, they received word from Mission Control that their work on the battery was showing good results, triggering relief as they moved on to more work. In all, their spacewalk lasted 7 hours and 17 minutes.
At the start of their outing, the astronauts took a moment to get used to moving around in the vacuum of space — dubbed a "translation adaptation." They then set about preparing their tools for replacing a failed power controller in the system that collects and distributes solar power to the space station's systems.
The charger failed after Koch's last extravehicular activity, or EVA, as spacewalks are known in NASA speak, when she and fellow astronaut Andrew Morgan installed new batteries on the outside of the station last week.
The historic all-female spacewalk has been months in the making.
It was originally supposed to happen in March, with astronaut Anne McClain joining Koch. But the station was short one functioning, medium-sized spacewalking suit, the right size for both women. Koch went instead with colleague Nick Hague.
"As much as it's worth celebrating the first spacewalk with an all-female team, I think many of us are looking forward to it just being normal," veteran astronaut Tracy Caldwell Dyson said on NASA's live coverage of the spacewalk.
"I think if it signifies anything," she added, "it is to honor the women who came before us, who were skilled and qualified — and didn't get the same opportunities we get today because it is so normal."
Koch, an electrical engineer, had done previous spacewalks, including her first with Hague in March. She's seven months into a planned 11-month stay on the station. Friday's EVA is a first for Meir, who is also on her first spaceflight.
By forming an all-female team, Koch and Meir's EVA is a first for any nation in space.
"With today's first all-woman spacewalk on the International Space Station led by NASA astronauts Christina Koch and Jessica Meir, America once again sets a precedent for women to lead in human space exploration," NASA Administrator Jim Bridenstine said of the historic event.
Bridenstine was part of a conference call from the White House, along with President Trump, Vice President Pence and the president's daughter and adviser, Ivanka Trump.
"What you do is incredible. It's so — you're very brave people," President Trump said. "I don't think I want to do it, I must tell you that. But you are amazing people."
"This is truly historic," Trump added.
"Thank you — we don't want to take too much credit," Meir replied, noting the other women who have performed spacewalks in the past. "For us, this is really just us doing our jobs."
Sally Ride became America's first woman in space (aboard Space Shuttle Challenger) in 1983, 20 years after Russian cosmonaut Valentina Tereshkova was launched into orbit on Vostok 6. A year after Ride's first flight, another Russian woman, Svetlana Savitskaya, became the first woman to walk in space, followed a few months later, on Oct. 11, 1984, by America's first female spacewalker, Kathryn Sullivan.
Meir is the 15th female spacewalker; by comparison, 213 men have walked in space, according to The Associated Press.
The first person to walk in space was Soviet cosmonaut Alexei Leonov, who died last week. After he set the mark in March 1965, he was followed less than three months later by American Ed White.