NASA astronauts Chris Cassidy and Robert Behnken stepped outside the International Space Station (ISS) Thursday to continue efforts to complete a three-and-a-half-year project to upgrade the station’s batteries, the space agency said.Cassidy and Behnken have been working to replace aging nickel-hydrogen batteries with new lithium-ion batteries delivered to the station on a Japanese cargo ship in May. In all, NASA said 12 spacewalks will have been performed since January 2017 to change out batteries for eight power channels used to route electricity on the station.Thursday’s extravehicular activity is expected to last up to seven hours.NASA Astronauts Take Space Walk to Upgrade ISS BatteriesSpacewalk continues mission begun last week to upgrade ISS batteriesThe final spacewalk to complete the project is scheduled for next Tuesday and it will be somewhat historic. When the two astronauts once again step outside the ISS that day, it will mark the 300th spacewalk involving U.S. astronauts since Ed White stepped out of his Gemini 4 capsule on June 3, 1965.The space agency said the final two spacewalks will be the 230th and 231st spacewalks in the history of space station assembly, maintenance, and upgrades. They also will be the ninth and 10th for Cassidy and Behnken, who will join former NASA astronauts Michael Lopez-Alegria and Peggy Whitson with the most spacewalks by Americans.
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