Spacewalkers resume solar power system upgrade on International Space Station

Astronauts Josh Cassada and Frank Rubio floated outside the International Space Station on Saturday to install a third set of deployed solar panel covers, as part of an ongoing power system upgrade, and to isolate damaged circuits in one of the original lab panels.

Floating in the Quest airlock compartment, Cassada and Rubio put their spacesuits on battery power at 7:16 a.m. ET, officially kicking off a planned seven-hour spacewalk, the 256th dedicated to the assembly and maintenance of the station and the 11th so far this year.

For identification, Cassada, call sign EV-1, wears a red striped jumpsuit and uses helmet camera #22 while Rubio, EV-2 uses an unmarked jumpsuit with helmet camera #20 The two men are on their second spacewalk.

The purpose of the excursion is to install a new set of ISS Roll-Out Solar Array — IROSA — blankets that were flown to the space station aboard a SpaceX Dragon freighter last month.

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

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 supply electricity to eight main circuits, or power channels, during the day to run the lab’s systems and recharge the batteries. Batteries provide power during orbital darkness.

The first set of original equipment covers, located at the left end of the powerhouse power girder, have been in service for over 20 years. Later wings were added in 2006, 2007 and 2009. All have suffered degradation over the years in the space environment and they do not generate as much power as when new.

As part of a $103 million upgrade, NASA is installing the smaller but more powerful IROSA blankets to increase production of the lab’s eight older original equipment blankets.

The first two IROSA covers were installed on the left outer arrays – the oldest on the station – during spacewalks in 2021. Cassada and Rubio planned to install one of the two new IROSAs on a right inner wing to increase the 3A power channel.

The second new IROSA will be attached to an interior left-side array during a spacewalk on Dec. 19 to augment the 4A power channel. A final batch of IROSA should be delivered to the station next year.

IROSAs were tightly coiled and folded in the middle for launch. After mounting the assembly to previously installed brackets, Cassada and Rubio planned to unfold the 3A IROSA, lock it open, and release the retainers that will allow the covers to unfold to their 60-foot length.

The new blankets had to be connected to the station’s power grid during orbital darkness when no electricity is generated.

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 outwards at a 10 degree angle to minimize the shadow they cast on the board below.

“The first two arrays performed remarkably well,” said Matt Pickle, development projects manager at Boeing, in a NASA statement. “Solar cells are immensely more powerful than previous generations.”

Once all six deployment bays are installed, the overall power output will be increased by 20-30%, roughly matching the output of the original bays when new.

The last two of the six IROSAs currently under contract will be launched next year. It is not yet known whether NASA will purchase two final IROSAs to augment the station’s original eight coverages.