NASA spacewalkers (from left) Bob Behnken and Chris Cassidy set up the outside of the Tranquility module for the future installation of the NanoRacks airlock. (Credit: NASA)
NASA spacewalkers (from left) Bob Behnken and Chris Cassidy set up the outside of the Tranquility module for the future installation of the NanoRacks airlock, July 21, 2020. (Credit: NASA)

U.S. space agency astronauts Bob Behnken and Chris Cassidy Tuesday floated out of the International Space Station (ISS) on their fourth and final spacewalk to complete the upgrade of the station’s power supply system.

Tuesday’s spacewalk is the fourth for the astronauts in under a month, and the 10th spacewalk in each of their careers, tying the U.S. record set by previous space station residents. It is the 12th total spacewalk since 2017 to upgrade the station’s batteries, and the 231st extravehicular mission in the history of the ISS.

In under two weeks, Behnken and fellow commercial crew astronaut Doug Hurley, who monitored the spacewalk from inside the ISS, will depart the orbiting complex in the same SpaceX Dragon crew capsule in which they arrived at the end of May.

SpaceX is aiming for a splashdown off the Florida coast August 2, the first just landing for astronauts in 45 years. Weather permitting, the Dragon capsule will parachute into the Gulf of Mexico off the Florida Panhandle.

NASA administrator Jim Bridenstine said once Tuesday's spacewalk is finished, the astronauts are going to be focused on returning home.

The first-stage booster used to launch Behnken and Hurley on May 30 blasted off for a second time Monday from Cape Canaveral. It landed on a floating platform in the Atlantic after hoisting a satellite for South Korea's military, to be used again for another flight.