Christina Koch and Jessica Meir ventured out of the International Space Station just before 7 a.m. to replace batteries on some of the solar panels on the station's exterior.
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Koch and Meir made history in October when they completed the first all-female spacewalk. Koch made headlines again in December when she broke the record for the longest single spaceflight by a woman.
The two astronauts will perform a second spacewalk Monday to finish replacing the batteries.