NASA astronaut Christina Koch floats on the end of the International Space Station’s robotic arm during a spacewalk. (NASA via YouTube)

For the first time in history, two women teamed up today for a spacewalk.

NASA astronauts Christina Koch and Jessica Meir began the operation to fix a faulty electrical power system on the International Space Station at 7:38 a.m. ET (4:38 a.m. PT)  — setting a new precedent in the process.

During a break in the action, the spacewalkers took a congratulatory phone call from the White House.

“You’re brave people — I don’t think I want to do it, I must tell you that. But you are amazing people,” President Donald Trump told the pair. “They’re conducting the first-ever female spacewalk to replace an exterior part of the space station.”

Meir corrected the record in her reply.

“We don’t want to take too much credit, because there have been many other female spacewalkers before us,” she said. “This is just the first time that there have been two women outside at the same time.”

Meir said she and Koch were “just coming out here and doing our jobs today.”

“At the same time, we recognize that it is a historic achievement, and we do of course want to give credit to all those that came before us,” she told the president. “There has been a long line of female scientists, explorers, engineers and astronauts, and we have followed in their footsteps to get us where we are today. We hope we can provide an inspiration to everybody — not only women, but to everybody that has a dream, that has a big dream, and is willing to work hard to make that dream come true.”

This was the first spacewalk for Meir, a space rookie who arrived at the station last month. It was the fourth spacewalk for Koch, who’s been on the space station since March and is due to set a 328-day women’s record for continuous time in space next year. The operation was originally set to last five and a half hours, but things went so smoothly that the pair agreed to do an hour’s worth of extra work..

Another woman astronaut, Stephanie Wilson, coordinated the spacewalk at NASA’s Mission Control in Houston.

Ken Bowersox, NASA’s acting associate administrator for human exploration and operations, said it’s taken so long to have an all-female spacewalk team in part because of physical characteristics and equipment limitations. “It’s a little bit like playing in the NBA,” he said.

Historically, NASA has favored taller astronauts for spacewalks, and those astronauts tended to be men, Bowersox explained. But with a more diverse astronaut corps, NASA is devoting more attention to accommodating a wider range of body sizes — and spacesuit sizes.

The first pairing of two spacewalking women was originally scheduled in March, but that plan had to be put off when NASA decided they couldn’t get two medium-size spacesuit torsos ready on schedule. Instead, the spacewalk lineup was shuffled to have the women working alongside male crewmates.

Koch and Meir were well-equipped for today’s spacewalk, which addressed an urgent problem on the space station.

The space station’s crew is in the midst of a battery replacement campaign that requires five spacewalks to complete. Two spacewalks have already been done, and Koch and Meir were scheduled to take their turn on Oct. 21.

But just a few days ago, mission managers determined that a battery charge-discharge unit, or BCDU, wasn’t working properly with a new set of batteries.

The BCDUs regulate the amount of electrical charge that the station’s solar arrays put into the power system’s batteries. NASA says the unit’s failure after 19 years of operation doesn’t immediately affect station operations or crew safety, but it does prevent the new batteries from providing the expected increase in power.

A similar BCDU failure occurred in April, and the station is now down to only three or four spares. Mission managers were anxious to resolve the latest glitch and figure out what the problem is.

“It’s absolutely a concern at this point, when you don’t know what’s going on,” Kenny Todd, NASA’s manager of space station operations and integration, told reporters when the schedule change was announced. “We’re still scratching our heads looking at the data.”

Koch and Meir replaced the bad BCDU and stowed it inside the station in businesslike fashion, pausing only briefly at times to enjoy the view. There was plenty of time left over to work on get-ahead tasks, such as adjusting a layer of insulation on the space station’s exterior and installing some fittings on the European Space Agency’s Columbus laboratory module.

NASA had planned to conduct three more battery-replacement spacewalks this month, but those have been put on hold pending the results of today’s repair job.

The early verdict was a thumbs-up: “We show that the battery charge-discharge unit is fully powered up and working,” Mission Control’s Wilson told the spacewalkers.

“That is awesome news, thank you,” Koch replied. Meir seconded that emotion: “Amazing news, Stephanie. That makes us very happy,” she said.

The official end of the spacewalk was called at 2:55 p.m. ET (11:55 a.m. PT), seven hours and 17 minutes after it started.

The need to address the BCDU issue is why NASA reshuffled the spacewalk schedule — and changed the timing for a milestone in space history.

Women have been doing spacewalks ever since Soviet cosmonaut Svetlana Savitskaya ventured outside the Salyut 7 space station in 1984, followed months later by NASA shuttle astronaut Kathryn Sullivan’s outing. But those spacewalkers, and all of the women who followed in their footsteps, did their work in the company of men. Today’s spacewalk finally broke that habit.

During the buildup to the first all-female spacewalk, Megan McArthur, deputy chief of NASA’s astronaut office, said the milestone merely reflects how the astronaut corps has evolved from its all-male beginnings.

“It will be an exciting event, something we will reflect on certainly after the fact,” she said. “But in truth, in terms of looking at the workload that we have coming forward, this was the right crew to send out to do this set of tasks. All of our crew members are completely qualified to do this, and the fact that it will be two women just is a reflection of the fact that we have so many capable, qualified women in the office.”

NASA astronaut Tracy Caldwell Dyson voiced a similar perspective today in her spacewalk commentary on NASA TV. “I think the milestone is that, hopefully, this will now be considered normal,” she said.

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