Astronauts unfurl fourth roll-out solar array outside International Space Station

NASA astronaut Josh Cassada near the spool of the roll-out solar array during deployment Thursday. Credit: NASA TV / Spaceflight Now

Another roll-out solar array was installed and deployed by astronauts Frank Rubio and Josh Cassada outside the International Space Station on on a spacewalk Thursday, a day later than previously planned after the space station needed to dodge a piece of space junk.

Rubio and Cassada continued a multi-year upgrade to the space station’s electrical system, adding the fourth of six planned roll-out solar arrays to the station’s power truss.

The first two roll-out solar arrays were installed in June 2021 after delivery on a SpaceX Dragon cargo ship. Another SpaceX resupply mission carried the next pair of roll-out solar arrays to the station last month, and Rubio and Cassada installed and unfurled the first of those two units on a spacewalk Dec. 3.

The spacewalk Thursday was originally scheduled for Monday, but space station managers delayed the excursion after a Russian Soyuz crew ferry ship sprung a coolant leak Dec. 14. Instead of using the space station’s robotic arm to support the spacewalk Monday, mission control extended the arm to inspect the Soyuz MS-22 spacecraft to aid the investigation into the cause of the leak.

NASA rescheduled the spacewalk for Wednesday, but officials called it off as Rubio and Cassada were preparing for the excursion to allow the space station to steer out of danger from a fragment of a Russian Fregat rocket stage. A Russian Progress cargo freighter docked at the station fired its thrusters for 10 minutes and 21 seconds at 8:42 a.m. EST (1342 GMT) Wednesday to “provide the complex an extra measure of distance away from the predicted track of the debris,” NASA said in a statement.

Without the maneuver, engineers estimated the space debris could have passed less than a quarter-mile from the station, according to NASA.

Rubio and Cassada resumed their spacewalk preps Thursday, put on their self-contained pressure suits, and exited the Quest airlock to start their work with the roll-out solar array. The spacewalk officially began when the astronauts switched their spacesuits to internal battery power at 8:19 a.m. EST (1319 GMT).

The astronauts headed to the starboard, or right, side of the lab’s solar power truss, where the station’s robotic arm placed two new ISS Roll-Out Solar Array, or iROSA, units after extracting them from the trunk of SpaceX’s Dragon cargo capsule. The Dragon spacecraft delivered the solar arrays to the space station Nov. 27, along with several tons of supplies and experiments.

Rubio and Cassada transferred the first iROSA unit to the space station’s starboard 4, or S4, right-side truss segment during a Dec. 3 spacewalk. On Thursday, the spacewalker completed similar tasks to move the other iROSA unit to the opposite side of the power truss, which stretches as long as a football field.

NASA astronaut Frank Rubio was designated EV-1 on the spacewalk Thursday. NASA astronaut Josh Cassada was designated EV-2. This was the third spacewalk for each astronaut. Credit: NASA TV / Spaceflight Now

The new solar arrays are wrapped around spools for launch and then unroll like a yoga mat once installed onto their mounting brackets on the space station.

After releasing bolts and launch restraints on the solar array spool, Cassada took position on a foot restraint on the end of the Canadian-built robotic arm and carried the 750-pound (340-kilogram) iROSA unit to the port 4, or P4, truss segment.

Rubio and Cassada positioned the spool onto a mounting bracket put in place on the P4 truss during a spacewalk last year. They unfolded the iROSA unit on its hinge, then installed bolts to secure it into place and mated electrical connectors to link the new iROSA unit to the space station’s electrical system. Then the astronauts put in a Y cable to route power generated by both the new roll-out solar array and the original P4 solar panel into the lab’s power grid.

The 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.

Once the new iROSA unit was mechanically and electrically integrated onto the station’s P4 truss, the astronauts released clamps keeping the roll-out solar array spooled in its launch configuration. That allowed the solar array to gradually unroll using strain energy in the composite booms supporting the solar blanket. The design of the deployment mechanism eliminates the need for motors to drive out the solar array.

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

It took about 10 minutes for the solar array to unroll to its fully extended configuration, stretching about 63 feet long and 20 feet wide (19-by-6 meters), roughly half the length and half the width of the station’s original solar panels. The solar array blanket is canted at an angle relative to the original solar panel on the P4 truss, allowing sunlight to illuminate the new and old arrays.

Despite their smaller size, each of the new arrays generate about the same amount of electricity as each of the station’s existing solar panels.

Once the solar array unfurled, the astronauts adjusted tensioning bolts to secure the iROSA blanket in place.


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 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 new solar array deployed Thursday will produce electricity for the space station’s 4A power channel.

The original solar panels launched on four space shuttle missions from 2000 to 2009. As expected, the efficiency of the station’s original solar arrays has degraded over time. NASA is upgrading the space station’s power system with the new roll-out solar arrays — at a cost of $103 million — 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. That’s a 30% increase in power generation capability. The enhancement will also accommodate new commercial modules planned to launch to the space station.

The first pair of new roll-out solar arrays launched to the space station last year, and were installed over the station’s oldest set of original solar panels on the P6 truss section, located on the far left end of the outpost’s power truss. Two more iROSA units are slated to launch on a SpaceX resupply mission next year.

The new solar arrays were supplied to NASA by Boeing, Redwire, and a team of subcontractors.

Once Rubio and Cassada finished their work, they headed back to the Quest module and repressurized the airlock compartment to wrap up the spacewalk at 3:27 p.m. EST (2027 GMT). The excursion lasted 7 hours and 8 minutes.

The spacewalk Thursday was the third in the careers of Cassada and Rubio, and the 257th spacewalk since 1998 in support of International Space Station assembly and maintenance.

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