Astronauts Chris Cassidy and SpaceX's Crew Robert Behnken are continuing a mission to replace ageing nickel-hydrogen batteries outside the International Space Station.
The operation could take as long as seven hours to complete. The batteries are part of the power system that's fed by eight solar arrays attached to the ISS.
Behnken arrived at the station on May 31 along with Doug Hurley aboard SpaceX's Crew Dragon. Cassidy is the commander of Expedition 63 and arrived in April.
It's the second spacewalk for the two after a successful spacewalk last week.
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