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NASA astronauts Jessica Meir (left) and Christina Koch (right) to prepare to leave the hatch of the International Space Station and begin the historic first-ever all-female spacewalk.

The astronauts replaced a faulty battery charge discharge unit (BCDU) that failed to activate following the Oct. 11 installation of new lithium ion batteries on the space station's exterior structure. The BCDUs regulate the amount of charge put into the batteries that collect energy from the station's solar arrays to power station systems during periods when the station orbits during nighttime passes around Earth. Though the BCDU failure has not impacted station operations or crew safety, it does prevent the new batteries from providing increased station power.