Spacewalkers unfurl first of six new space station solar arrays

Astronauts Thomas Pesquet and Shane Kimbrough, at left, work with the ISS Roll-Out Solar Array during a spacewalk Sunday. Credit: Oleg Novitskiy/Roscosmos

Astronauts Thomas Pesquet and Shane Kimbrough floated outside the International Space Station Sunday to deploy and unroll a new solar array blanket after encountering spacesuit glitches and an interference issue during a previous excursion Wednesday.

Pesquet and Kimbrough switched their spacesuits to battery power at 7:42 a.m. EDT (1142 GMT) Sunday to begin a planned six-and-a-half hour spacewalk.

The astronauts moved from the space station’s Quest airlock to the far port, or left, side of the lab’s solar power truss. Once in place, Pesquet and Kimbrough completed tasks they started during Wednesday’s spacewalk.

The astronauts lost time while ground teams evaluated an issue with the controls and display module on Kimbrough’s suit Wednesday. Then mission control discussed momentary glitch with a sublimator, part of the cooling system on Kimbrough’s suit.

The astronauts continued the spacewalk Wednesday and moved a new ISS Roll-Out Solar Array, or iROSA, unit from a temporary mounting fixture to the far port side of the station’s truss. Once at the P6 solar array work site, the astronauts attached the iROSA to a mounting fixture installed on a preparatory spacewalk earlier this year, then attempted to unfold the unit like a book.

But the astronauts ran into some interference as they tried to unfold the iROSA unit. With Pesquet and Kimbrough already running behind schedule due to the earlier spacesuit issues, mission control called it quits and told the astronauts to head back inside the space station.

The spacewalk Sunday was originally planned to install a second iROSA solar array on the other side of the P6 truss. But after losing time on the previous spacewalk, Pesquet and Kimbrough had to catch up with the work left undone Wednesday.

Kimbrough, a former U.S. Army helicopter pilot, swapped spacesuits for Sunday’s excursion after the troubles with his suit Wednesday.

The International Space Station has eight power channels, each fed with electrical power generated from one solar array wing extending from the station’s truss backbone. The original solar panels launched on four space shuttle missions from 2000 to 2009.

As expected, the solar panel efficiency has degraded over time. NASA is upgrading the space station’s power system with the new roll-out solar arrays, which will partially cover six of the station’s eight original solar panels.

When all six iROSA units are deployed on the station, the power system will be capable of generating 215 kilowatts of electricity to support at least another decade of science operations. The enhancement will also accommodate new commercial modules planned to launch to the space station.

Each of the new iROSA wings will be canted at an angle of 10 degrees relative to the space station’s existing solar panels. Credit: NASA

The first pair of iROSA wings will go on the oldest solar panel module — named P6 — on the far left, or port, side of the space station. They launched to the space station on a SpaceX Cargo Dragon capsule earlier this month. The new solar arrays were supplied to NASA by Boeing, Redwire, and a team of subcontractors.

Fully deployed, the roll-out solar arrays stretch 63 feet long and 20 feet wide (19-by-6 meters), about half the length and half the width of the station’s current solar arrays. Despite their smaller size, each of the new arrays will generate about the same amount of electricity as each of the station’s existing solar panels.

A mounting bracket plugs the new arrays into the station’s power channels and rotary joints, which keep the solar wings pointed at the sun as the spacecraft races around Earth at more than 17,000 mph.

Early on in Sunday’s spacewalk, Pesquet and Kimbrough separated the two parts of the iROSA fixture on the 2B power channel at the P6 truss segment. The astronauts drove bolts to secure the array in place, then mated power cables to connect the new array to the space station’s electrical grid.

The cables were mated when the space station was flying over the night side of the Earth, when the old P6 solar array was not generating any power. Then the astronauts released clamps keeping the roll-out solar array spooled in its launch configuration.

Beginning at 11:24 a.m. EDT (1524 GMT), the array gradually unrolled using strain energy in the composite booms supporting the solar blanket. The design of the deployment mechanism eliminates the need for motors to drive the solar array.

The carbon fiber support booms were rolled back against their natural shape for storage during launch.

After about 10 minutes, the iROSA blanket reached its full length of 63 feet.

“Good news, you two,” Canadian astronaut Jenni-Sidey Gibbons radioed the spacewalkers from mission control in Houston. “You can probably can see most of what we can see. We’re tracking a full and good deploy of that solar array, so well done both of you.”

Pesquet then adjusted tensioning bolts to secure the iROSA blanket in place.

The astronauts then headed back in-board on the space station’s truss to prep a second iROSA unit, which Pesquet and Kimbrough will move to the P6 truss segment during a spacewalk tentatively scheduled for Friday, June 25.

The astronauts will connect the second iROSA unit to the 4B power channel on the opposite side of the P6 truss from the blanket they deployed Sunday. If all goes well on Friday’s excursion, they will repeat the steps they accomplished Sunday to unroll the second iROSA blanket.

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