On Wednesday morning, NASA astronaut Shane Kimbrough and European Space Agency astronaut Thomas Pesquet will conduct a spacewalk to begin the installation of new solar arrays. The panels will help provide a power boost to the space station.
The walk is scheduled to begin around 8 a.m. ET, with live coverage on NASA's TV channel and website starting at 6:30 a.m. ET. The spacewalk is expected to last about six-and-a-half hours.
Pesquet will be wearing red stripes on his spacesuit as extravehicular crew member 1 and Kimbrough will wear the suit without stripes as extravehicular crew member 2.
The two astronauts will continue these upgrades during a spacewalk on Sunday. These are the 239th and 240th spacewalks in support of assembling, maintaining and upgrading the station.
Wednesday's spacewalk tasks include installing the first two out of six ISS Roll-Out Solar Arrays, called iROSAs, which will upgrade six of the eight power channels on the space station. The first array will be installed on the far left end of the station's backbone truss.
Kimbrough and Pesquet will install the second solar array on Sunday.
The solar arrays arrived at the space station on June 5 after launching on the 22nd SpaceX Dragon cargo resupply mission. The space station's robotic Canadarm2 was used to remove the solar arrays from the spacecraft last Thursday. The arrays are rolled up like carpet and are 750 pounds (340 kilograms) and 10 feet (3 meters) wide.
Once the arrays are unfurled and bolted into place by the astronauts, they will be about 63 feet (19 meters) long and 20 feet (6 meters) wide. This unfurling process will take about six minutes.
Once the astronauts put the initial bolts in place at the top, they'll let the array go and watch. This process won't be visible to cameras on the station given its location, so Kimbrough's high-definition helmet camera will capture this deployment.
Inside the space station, NASA astronaut Megan McArthur will help put the arrays into place using Canadarm2.
To protect the astronauts since they are working around electrical connectors, the ground crew has been busy conducting a plasma forecast to determine what kind of electrical charge the space station will be in during the walk, according to Kieth Johnson, spacewalk officer.
Metallic aspects of the spacesuits will be covered to prevent metal contact that could cause electric shock. The time of the spacewalk has been planned so the giant solar arrays will be in darkness and not generating power.
These will be the seventh and eighth career spacewalks for Kimbrough and the third and fourth for Pesquet -- and it's not the first time these two have taken a walk outside the space station together.
Kimbrough and Pesquet were on the space station in 2017 and previously conducted two spacewalks together to replace aging nickel-hydrogen batteries with new, longer-lasting lithium-ion batteries.
While the current solar arrays on the space station are still functioning, they have been supplying power to the space station for more than 20 years and are showing some signs of wear after long-term exposure to the space environment. The arrays were originally designed to last 15 years.
Erosion can be caused by thruster plumes, which comes from both the station's thrusters as well as the crew and cargo vehicles that come and go from the station, said Dana Weigel, deputy manager of the International Space Station Program.
"The other factor that affects our solar arrays is micrometeorite debris. The arrays are made of a lot of small power strings, and over time those power strings can degrade if they're hit by debris," she said.
The new solar arrays will be placed in front of the current ones. This will give the space station a boost, increasing its total available power from 160 kilowatts to 215 kilowatts. It's also a good test for the new solar arrays because this same design will power parts of the Gateway lunar outpost, which will help humans return to the moon through NASA's Artemis program in 2024.
"The exposed portion of the old arrays will still be generating power in parallel with the new arrays, but those new Iris arrays have solar cells on them that are more efficient than our original cells," Weigel said. "They have a higher energy density and together in combination may generate more power than what our original array, when it was new, did on its own."
The new arrays will have a similar 15-year expected life span. However, since the degradation on the original arrays was expected to be worse, the team will monitor the new arrays to test their true longevity.
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