The international space stations iROSA (ISS roll-out solar panel) The solar array upgrade, which began in 2021, finished its initial upgrade plan with the successful installation of the last two arrays this month. The arrays for power channels 1A and 1B were flown to the ISS aboard Cargo Dragon flight CRS-28 and then installed in a pair of EVAs by NASA astronauts Steve Bowen and Woody Hoburg.

The iROSA project was initiated due to continued degradation of the Station’s existing solar arrays after years in low Earth orbit. The original solar array complement, finished in March 2009 with the installation of the S6 truss, was capable of 240 kilowatts when new. However, the radiation environment in orbit has degraded the arrays to the point where they can now only generate 160 kilowatts.

A NASA diagram of the progress of installing the iROSA solar array on the ISS’s outer truss segments. (Credit: NASA)

The installation of six new iROSA arrays, each capable of generating 20 kilowatts, and built by Redwire, would bring back much of the stations’ lost power generation capacity, with the new set of arrays bringing the ISS back around its initial power generation.

This upgrade will serve the Station until the end of its life, expected in 2030, and a new pair of iROSAs are expected to fly to the ISS in 2025 to further boost power to the ISS, as announced during EVA-88 broadcast. This would bring the total number of iROSA arrays installed on the ISS to eight.

A prototype ROSA array was brought to the Station aboard CRS-11 in June 2017 and successfully tested at the Station Canadarm2 end for 12 days. The iROSA upgrade project for the Station began with spacewalks in February and March 2021 to install iROSA mounting kits to power channels 2B and 4B. The astronauts later installed the first pair on power channels 2B and 4B during a trio of EVAs in June 2021.

This was followed by a spacewalk in September 2021 and another in March 2022 to install the next pair of mounting brackets for the iROSAs to be installed on power channels 3A and 4A. A pair of EVAs followed in December 2022 to install those panels. Additionally, one EVA in November 2022 was needed along with three EVAs in early 2023 – January, February and April – to pave the way for the final installations of iROSA in June.

The positioning of the new IROSAs on the Station’s existing solar panels. (Credit: NASA/Boeing)

ISS US EVA-87 commenced on Friday, June 9 at 8:24 AM CDT (13:24 UTC) with the opening of the hatch on the Quest airlock module. Astronaut Steve Bowen, as EV1 with red stripes on his spacesuit, began his ninth spacewalk, with EV2 Woody Hoburg following as he began his first-ever EVA.

The astronauts’ primary task was to install the iROSA array for feeder channel 1A, with the installation site on the S4 mast. The two iROSA arrays that had been activated on CRS-28 had been removed from the trunk of the Dragon and installed on the Mobile Transporter prior to EVA-87.

Astronaut Woody Hoburg on Canadarm2 during EVA-87. (Credit: NASA)

The duos first task, after retrieving the tools they would need, would be to release the array intended for 1A and transport it to the 1A mod kit job site. Woody Hoburg was the astronaut on the far end of Canadarm2 carrying the array to the construction site, while Sultan AlNeyadi operated the arm from inside the Station.

The astronauts installed the array on the mod kit and secured it using the Pistol Grip Tool (PGT), originally developed by NASA for servicing the Hubble Space Telescope. Bowen and Hoburg also installed cables to connect the arrays to the ISS’s electrical system, and this had to be done during orbital night to avoid electric shock from stray current.

Once all installation activities were completed, the iROSA array was deployed and the deployment went smoothly. Hoburg finished unscrewing two bolts to allow the turnbuckles to work, to release and tighten the panel. Meanwhile, during the array installation process, controllers were faced with longer-than-usual signal outages due to the recent impact of Typhoon Mawar on Guam which affected a relay station.

With deployment complete and astronauts ahead of schedule, Bowen and Hoburg worked on some progress tasks for EVA-88. Bowen rotated the beams that held the upper iROSA, to allow access to the lower iROSA on EVA-88.

He and Hoburg then worked to release the iROSA for feeder channel 1B from one end of its temporary siding on the Station. It took about 245 bolt turns to complete, so finishing this would definitely help the astronauts during the next EVA.

Bowen and Hoburg cleaned their safety chains, finished their EVA activities and entered the Quest airlock. EVA-87 concluded at 2:28 PM CDT (19:28 UTC) after six hours and three minutes, with Bowen’s spacewalk experience now totaling 60 hours and 22 minutes while Hoburg finished her first EVA.

EVA-87 by numbers. (Credit: NASA TV)

Sultan Al Neyadi and Francisco Rubio were the intravehicular (IV) crew members for this spacewalk, while CSA astronaut Jenni Sidey-Gibbons was the IV ground crew member who spoke to the astronauts. Flight Controller Megan Shutilka, Chief Spacewalk Officer Brandon Lloyd, and Flight Director Diane Dailey were also on duty for this EVA.

EVA-87 was the fifth spacewalk of Expedition 69 and the seventh conducted by the ISS so far in 2023. The 264th EVA to the ISS was a complete success, but the initial project to enhance the ISS’s solar array was not yet finished.

Steve Bowen and Woody Hoburg were selected to lead EVA-88 six days later, with astronauts Rubio and AlNeyadi again crew in orbit IV. Astronaut Sidey-Gibbons was again on the ground IV, while Brandon Lloyd served as flight director. Megan Shutilka became the chief spacewalk officer.

Mission Control in Houston during EVA-87. Flight Controller Megan Shutilka is seen here with astronaut Jenni Sidey-Gibbons to her right. Brandon Lloyd is to Megans’ left. (Credit: NASA TV)

EVA-88 began at 7:42 AM CDT (12:42 UTC) Thursday, June 15, with Woody Hoburg taking the EV1 designation and red stripes for his second EVA, while Steve Bowen became EV2 with the all-white spacesuit for her tenth EVA.

The two began their spacewalk by installing lifelines and retrieving their tools as usual, and finished releasing the final iROSA array from its carrier. The iROSA was moved to the 1B runner mount kit, located on the S6 truss, with Steve Bowen at the end of the Canadarm2.

After the transfer was complete, astronauts Hoburg and Bowen installed the iROSA on its mounting kit similar to the process used on EVA-87. They had to wait to connect the new array to the ISS electrical system, as they were ahead of schedule and needed to run the task during orbital night.

The astronauts used the time to start cleaning their yard as a to-do task. Once the Station moved into the orbital night, Hoburg and Bowen connected the iROSA’s cables to the Station’s electrical system. There was eight minutes of data loss during this activity, as well as an unexpected loss of voice. As in EVA-87, typhoon damage in Guam was forcing a station in Canberra, Australia to take over some data transmission duties.

The 18.2-metre-long, 6-metre-wide iROSA array successfully deployed despite an anomaly that should not affect power generation capacity, and Bowen finished loosening two bolts to allow the array to be tensioned. After this task was accomplished, the two astronauts finished clearing the construction site, performed preliminary tasks involving a connector and footrest, and headed to the Quest airlock to complete the spacewalk.

The iROSA for feed channel 1B is implemented during EVA-88. (Credit: NASA TV)

EVA-88 was completed at 1:17 PM CDT (18:17 UTC), after five hours, 35 minutes, with Steve Bowens’ total EVA time now set at 65 hours, 57 minutes, and total time Woody Hoburg’s hour at 11 hours 38 minutes. With this EVA, Steve Bowen surpassed Drew Feustel as the third most experienced astronaut of all time, while also setting the record for most spacewalks by a US astronaut. The ISS has seen 265 spacewalks so far, including eight this year and six for Expedition 69, for a total time of 70 days, 3 hours and 27 minutes.

This year has seen two complex and challenging ISS upgrade tasks, one for the power system and the other for adding the Nauka module to the Russian segment, successfully completed after multiple EVAs have been performed over the past two years . The iROSA solar array upgrade project required 15 EVAs from 2021 to 2023, while the Nauka science module outfitting required 11 EVAs plus one more to connect the Prichal module to Nauka and the ISS during the same time period.

Cosmonauts Dmitry Petelin (left) and Sergey Prokopyev (right) near the airlock of the Nauka experiment during EVA-58. (Credit: NASA TV)

The next EVA on the Station is scheduled for one week by EVA-88. Russia’s EVA-59 is scheduled for Thursday, June 22, with cosmonauts Sergey Prokopyev and Dmitry Petelin activating the experiment’s recently installed airlock on Nauka. EVA plans for the US side of the Station beyond this month have not yet been set.

(Main image: Astronaut Steve Bowen with an iROSA array during EVA-87. Credit: NASA)

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