The spacewalk started at 7:12 am ET and is expected to last about seven hours.
During the spacewalk, Cassidy and Behnken will install a protection unit used to store tools for the Canadian Space Agency’s Dextre robot, as well as two robotic external leak location units. Dextre can use them to detect ammonia leaks. Ammonia is used in the station’s cooling system.
Working on the station’s backbone, the astronauts will also remove two devices at the base of the station’s solar panels that were used prior to launch.
Astronauts will prepare the Tranquility module for the NanoRacks commercial lock, which will arrive at the station on a SpaceX cargo flight later this year. The airlock will help with the deployment of experiments.
The last tasks of the day will include routing ethernet cables and removing a lens filter cover on an external camera.
A future spacewalk later this year will complete the power system upgrades to the space station by replacing a 2019-installed lithium-ion battery that was shortened.
It will be the culmination of the power system upgrades to the space station that have occurred in the past three and a half years to replace 48 aging nickel-hydrogen batteries with 24 new lithium-ion batteries.
However, these power system upgrades are nothing. how to replace the batteries in your TV remote control. New batteries have a mass of 428 pounds each.
Updates have required 11 spacewalks from January 2017, until now, to replace the batteries.
Both astronauts are veteran spacewalkers. This was the tenth outdoor adventure for both Cassidy and Behnken, according to NASA. This puts them in a tie with NASA astronauts Michael Lopez-Alegria and Peggy Whitson for most Americans’ spacewalks.
Last week, the agency announced that Behnken and Hurley will return in SpaceX’s Crew Dragon on August 2.
During the spacewalk, Behnken will be crew member 1 in the red striped spacesuit and Cassidy will be crew member 2 in the non-striped suit.
Hurley helped Cassidy and Behnken put on their space suits and will support astronauts from inside the space station.
Although this is the 231st spacewalk in the history of assembling, maintaining, and updating the space station, it is the 300th spacewalk involving American astronauts.
The first spacewalk by an American astronaut was performed by NASA astronaut Ed White on June 3, 1965. He left the Gemini 4 capsule at 3:45 pm ET and stayed out of it for 23 minutes.
Gemini 4 circled Earth 66 times in four days. During the spacewalk, White started over the Pacific Ocean near Hawaii and returned to the capsule as they flew over the Gulf of Mexico.
He exited the spacecraft using a manual oxygen-jet pistol to push himself, attached to a 25-foot safety strap. NASA astronaut James McDivitt, on the mission with White, took photos of White in space from inside the capsule.
White later said the spacewalk was the most comfortable part of the mission, saying the order to end it was the “saddest moment” of his life, according to NASA.
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