The last spacewalk ever to be part of a space shuttle mission is underway outside the International Space Station. NASA’s Mike Fossum and Ron Garan started their 6-and-a-half hour spacewalk at 9:22 a.m. ET Tuesday, when they switched their spacesuits to battery power. Even though the two astronauts arrived at the ISS on a Russian Soyuz spacecraft earlier this year, the spacewalk is considered part of the last-ever shuttle mission of the Space Shuttle Atlantis. That’s because Fossum and Garan are retrieving a broken ammonia pump outside the space station that will return to Earth on Atlantis. They will also install the Robot Refueling Mission, a box of tools and satellite components that will allow the Canadian Dextre Robot to test whether it can handle tools to repair satellites in space.