ISS finishes initial iROSA upgrade with two EVAs this month

by Justin Davenport

The International Space Station’s iROSA (ISS Roll-Out Solar Array) solar panel upgrade, started in 2021, has finished its initial upgrade plan with the successful installation of the last two arrays this month. The arrays for the 1A and 1B power channels were brought to ISS aboard the CRS-28 Cargo Dragon flight and then installed in a pair of EVAs by NASA astronauts Steve Bowen and Woody Hoburg.

The iROSA project was started due to the ongoing degradation of the Station’s existing solar panels 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 iROSA solar array installation progress on the exterior truss segments on the ISS. (Credit: NASA)

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

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

A prototype ROSA array was flown up to the Station aboard CRS-11 in June 2017, and successfully tested on the end of the Station’s Canadarm2 for 12 days. The iROSA upgrade project for the Station started with spacewalks in February and March 2021 to install the iROSA mounting kits to power channels 2B and 4B. Astronauts subsequently 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 one 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. In addition, an EVA in November 2022 along with three EVAs in early 2023 – January, February, and April – were needed to prepare the way for the final iROSA installations in June.

The placement of the new IROSAs over the existing Station solar arrays. (Credit: NASA/Boeing)

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

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

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

The duo’s first task, after retrieving the tools they would need, would be to release the array meant for 1A and transport it to the 1A mod kit worksite. Woody Hoburg was the astronaut at the end of the Canadarm2 carrying the array to the worksite, while Sultan AlNeyadi operated the arm from within the Station.

The astronauts installed the array to the mod kit and bolted it down 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 electrical system, and this had to be done during orbital night to prevent electric shock due to stray current.

Once all installation activities were finished, the iROSA array was unfurled and the deployment succeeded without issues. Hoburg finished releasing two bolts to allow the tensioners to work, to release and to tighten the panel. Meanwhile, during the process to install the array, controllers had to deal with longer signal dropouts than usual due to Typhoon Mawar’s recent hit on Guam that affected a relay station.

With the deployment complete, and with the astronauts ahead of the timeline, Bowen and Hoburg worked on some get-ahead tasks for EVA-88. Bowen rotated beams that held the top iROSA, to allow access to the bottom iROSA on EVA-88.

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

Bowen and Hoburg cleaned up their safety tethers, finished their EVA activities, and entered the Quest airlock. EVA-87 ended 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 his first EVA.

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

Sultan Al Neyadi and Francisco Rubio were the intravehicular (IV) crewmembers for this spacewalk, while CSA astronaut Jenni Sidey-Gibbons was the ground IV crewmember that talked to the astronauts. Flight controller Megan Shutilka, lead spacewalk officer Brandon Lloyd, and Flight Director Diane Dailey also were on duty for this EVA.

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

Steve Bowen and Woody Hoburg were tapped to conduct EVA-88 six days later, with Astronauts Rubio and AlNeyadi being the on-orbit IV crew again. Astronaut Sidey-Gibbons was the ground IV again, while Brandon Lloyd acted as flight director. Megan Shutilka became the lead 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 Megan’s left. (Credit: NASA TV)

EVA-88 started at 7:42 AM CDT (12:42 UTC) on Thursday, June 15, with Woody Hoburg taking the EV1 designation and the red stripes for his second EVA, while Steve Bowen became EV2 with the all-white spacesuit for his 10th EVA.

The duo started their spacewalk by setting up safety tethers and retrieving their tools as usual, and they finished releasing the final iROSA array from its carrier. The iROSA was moved to the power channel 1B mounting kit, located on the S6 truss, with Steve Bowen being on the end of the Canadarm2.

After the move was finished, astronauts Hoburg and Bowen installed the iROSA on its mounting kit in a manner similar to the process they used on EVA-87. They had to wait to hook the new array to the ISS electrical system, as they were ahead of schedule and needed to perform the task during orbital night.

The astronauts used the time to start cleanup of their worksite as a “work-ahead” task. Once the Station moved into orbital night, Hoburg and Bowen attached the iROSA’s cables to the Station’s electrical system. During this task there was an eight minute data loss of signal, as well as an unexpected voice loss of signal. As in EVA-87, typhoon damage in Guam was forcing a station in Canberra, Australia to take up some data relay duties.

The 18.2 meter long and 6-meter wide iROSA array unfurled successfully, despite an abnormality that is not expected to affect power generation capability, and Bowen finished loosening two bolts to allow the array to be tensioned. After this task was done, the two astronauts finished cleaning  up the worksite, conducted work-ahead tasks involving a connector and a foot restraint, and headed to the Quest airlock to finish out the spacewalk.

The iROSA for the 1B power channel being rolled out during EVA-88. (Credit: NASA TV)

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

This year has seen two complex and involved ISS upgrade tasks, one for the power system, and the other for the Nauka module addition to the Russian segment, completed successfully after multiple EVAs were done in the past two years. The iROSA solar array augmentation project has taken up 15 EVAs from 2021 to 2023, while outfitting the Nauka science module took 11 EVAs plus another one to connect the Prichal module to Nauka and ISS during that same time span.

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

The next EVA on the Station is scheduled for one week from EVA-88. Russian EVA-59 is scheduled for Thursday, June 22, with cosmonauts Sergey Prokopyev and Dmitry Petelin will activate the experiment airlock recently installed on Nauka. EVA plans for the US side of the Station beyond this month are not yet set.

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

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