On early Friday, at 7:32 am ET, NASA astronauts Chris Cassidy and Robert Behnken began a spacewalk outside of the International Space Station. They did this to replace lithium-ion batteries for one of the station's power channels. They reached their work station after an hour of the spacewalk.

According to NASA, Cassidy's left wrist mirror detached and flew away when he exited the space station's hatch. Fortunately, it does not pose any risk to the crew, and the walk continued as planned.

The mirrors allow the astronauts to see aspects of their suits, such as labels, switches and actuator, which are out of their view. But with the left wrist mirror gone, Cassidy can use the right wrist instead while doing the spacewalk.

This will be Cassidy's seventh spacewalk, while this will be Behnken's eighth, which means that the two of them are veteran spacewalkers. On July 1, they will do another similar spacewalk.

NASA Spacewalk for Power Upgrades in ISS 

On May 31, Behnken and NASA astronaut Doug Hurley was launched from the United States aboard SpaceX's Crew Dragon during the Demo-2 mission and joined Cassidy on the space station.

These spacewalks mark the end of a series of power upgrades that started in January 2017 to replace nickel-hydrogen batteries with new lithium ion batteries that arrived last month on a Japanese cargo ship.

The main focus of the two spacewalks will be replacing batteries for one of the power channels on the far starboard truss of the station.

Unlike replacing batteries on a remote, these batteries are large, based on the animation that NASA showed in their tweet. Each of the batteries has a mass of 428 pounds.


The astronauts will be using foot restraint to help maintain their position and hand tools for adjustments as they make several trips back and forth along the truss to remove and replace each battery.

For both spacewalks, Cassidy is crew member I wearing a spacesuit with red stripes, while Behnken is crew member II in a suit with no stripes. Meanwhile, the two astronauts inside the station, Hurley and Russian cosmonaut Ivan Vagner will assist Cassidy and Behnken into their spacesuits. Hurley will operate the robotic arm of the station to support one of the astronauts who will do the spacewalks.

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Why Is It Important to Replace the Batteries?

Kenneth Todd, deputy International Space Station program manager, told the press on Wednesday that the battery replacements which will have a 20-year lifetime are expected to put the station in a much better configuration for a long time.

The next two spacewalks on summer will be focused on replacing the batteries on a second power channel.

Behnken told CNN innovation and space reporter Rachel Crane on a call to the station while discussing the spacewalk and the importance of replacing the batteries, that: "When the space station is in the sun, it's collecting energy and it needs to store for when it's in the dark, and so those batteries, as they're cycled time and time again, they wear down and need to be replaced. And so periodically that maintenance is required."

Moreover, Behnken is looking forward to the views of the Earth when they get free time. As an astronaut, when they do their first one, they try to do their best so that they can have another chance to do another one if the opportunity presents itself.

Once they have done a couple of spacewalks, it is important to take mental images of Earth and remember what it's like outside, Behnken said.

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