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Spacewalkers resume solar power system upgrade on International Space Station

Astronauts Josh Cassada and Frank Rubio floated outside the International Space Stationon Saturday, installed a third set of roll-out solar array blankets, part of an ongoing power system upgrade, and isolated damaged circuits in one of the lab's original arrays.

The seven-hour, 5-minute excursion went off without a hitch, increasing the station's power by 20 kilowatts in one of the smoothest spacewalks in recent memory. Flight Director Zeb Scoville congratulated the astronauts, saying "this is the kind of day that makes you want to clap your hands."

And he did just that, leading the mission control team in a round of applause, adding "let there be light! Great job, come on in!"

Frank Rubio, wearing an unmarked spacesuit, and Josh Cassada, wearing a suit with red stripes, prepare to install a new roll-out solar array blanket on the International Space Station, the third of six needed to augment the output of the lab's aging original-equipment arrays. NASA TV

Floating in the Quest airlock compartment, Cassada and Rubio switched their spacesuits to battery power at 7:16 a.m. EST, officially kicking off the 256th spacewalk devoted to station assembly and maintenance and the 11th so far this year.

The goal of the excursion was to install one of two ISS Roll-Out Solar Array blankets — IROSAs — that were carried to the space station aboard a SpaceX Dragon cargo ship last month.

The station is equipped with four huge solar wings, two on each end of a truss stretching the length of a football field. The arrays rotate like paddle wheels as the lab flies through space to maximize power generation.

Each of the four wings is made up of two sets of solar cells extending in opposite directions from a central hub. The eight sets of blankets deliver electricity to eight main circuits, or power channels, during daylight to operate the lab's systems and to recharge batteries. The batteries provide power during orbital darkness.

Astronaut Josh Cassada, anchored to the end of the space station's robot arm, manually holds a 750-pound rolled-up solar array blanket while being moved to its installation location. Crewmate Frank Rubio, wearing an unmarked suit, is visible at bottom right. NASA TV

The first set of original-equipment blankets, located on the left end of the station's power truss, has been in operation for more than 20 years. Subsequent wings were added in 2006, 2007 and 2009. All of them have suffered degradation from years in the space environment and they do not generate as much power as they did when they were new.

In a $103 million upgrade, NASA is installing the smaller but more-powerful IROSA blankets to augment the output of the lab's eight older, original-equipment blankets.

The first two IROSA blankets were installed on the left-side outboard arrays -- the oldest set on the station -- during spacewalks in 2021. Cassada and Rubio installed one of the two new IROSAs on a right-side inboard wing to augment power channel 3A.

The second new IROSA will be attached to an inboard left-side array during a December 19 spacewalk to boost power channel 4A. A final set of IROSAs are scheduled for delivery to the station next year.

The IROSAs were tightly rolled up and folded in the middle for launch. After mounting the assembly on previously installed brackets, Cassada and Rubio unfolded the 3A IROSA, locked it open and released restraints that allowed the blankets to unfurl to their 60-foot length.

A few moments later, flight controllers reported the new arrays were generating electricity as expected.

The new ISS Roll-Out Solar Array blanket unrolls on its own after installation, stretching out 60 feet to add about 20 kilowatts of electricity to the lab's power grid. NASA

With the installation work complete, Rubio made his way to the right-side outboard solar wing. One of those arrays feeds power channel 1B, which was knocked out of action 10 days ago by shorts in the array circuitry.

Rubio disconnected one of four power cables, isolating the damaged circuits and allowing flight controllers to restore 75 percent of the lost power. An IROSA scheduled for launch next year will be attached to the 1B array.

With their work complete, Cassada and Rubio made their way back to the Quest airlock to call it a day.

"Just thought I'd give you guys the general pulse of the control room, which is a bunch of smiling faces," astronaut Nick Hague radioed from mission control. "People are super excited about how much we got done today. So awesome job."

"Thank you so much," Cassada replied. "You've got two giant smiles out here as well. What an amazing team! You guys definitely deserve your Sunday off." In an aside to Rubio, he joked "Frank, what do you think we use this new station power to catch up on some college football?"

A NASA chart shows where the first three of six IROSA blankets have been installed. NASA

The IROSA blankets, about half the size of the original arrays, are more efficient and will eventually generate an additional 120 kilowatts of power. They were designed to be mounted on brackets at the base of an existing wing, extending outward at a 10-degree angle to minimize the shade they cast on the array below.

"The first two arrays have been performing outstandingly well," Matt Pickle, development projects senior manager at Boeing, said in a NASA release. "The solar cells are immensely more powerful than previous generations."

Once all six roll-out arrays are installed, overall power generation will be boosted 20% to 30%, roughly matching the output of the original arrays when they were new.

The final two of the six IROSAs currently under contract will be launched next year. It's not yet known whether NASA will buy two final IROSAs to augment all eight of the station's original blankets.

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