Astronauts conduct EVA to lay groundwork for final set of iROSA arrays


Astronauts Koichi Wakata and Nicole Mann are conducting a spacewalk that will enable the final set of upgraded ISS Roll-Out Solar Array (iROSA) “solar wings” to be installed on ISS sometime this summer.

The astronauts left the Quest airlock module on Friday, Jan. 20, at 7:14 AM CST (13:14 UTC) on US EVA-84. Koichi Wakataa, EV1, is wearing the suit with the red stripes while Nicole Mann, EV2, is wearing the suit with no stripes. This is the first spacewalk for both astronauts, and they will use EMUs 3004 and 3009.

The first task for Wakata will be to torque two collar bolts, M25 and M26, that will finish securing the partially installed mod kit to the truss. This task was left undone after the kit was installed due to time constraints during EVA-81.

After Wakata is done with this task on the S6 truss, he will translate over to the S4 truss and work with Mann on the iROSA kit installation for the 1A power channel. They will install a triangular fitting on top of the Beta Gimbal Assembly (BGA), then four trusses, two on each side of the triangular mount before torquing the bolts to finish the truss installation.

Mann’s next task will be to route the cables related to the iROSA mod kit. The cables will be installed when the 1A channel’s iROSA array is installed after it arrives at the ISS. Wakata will then complete the iROSA mounting installation for this EVA by routing cables to his side of the mounting bracket.

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Mann will then attach the DC to DC unit (DDCU) jumper cable to two different locations on the starboard truss before following Wakata to the airlock to finish the EVA. The jumper cable will allow autonomous rerouting of power to another electrical box if there is a failure.

However, the jumper cable attachment could be left for another EVA if time for a particular “get-ahead” item does not allow.

The get-ahead task in question involves routing cables on the 1B power channel on the S6 truss. This would require one of the EVA crewmembers to translate near the end of the starboard truss.

Another get-ahead that could be done is the retrieval for refurbishment of a robotic micro conical tool stored on the ISS exterior.

Nicole Mann shown with the DDCU jumper cable to be installed on EVA-84 (Credit: NASA)

Once the tasks scheduled for EVA-84 are finished, the way will be cleared for the installation of the last two iROSA arrays after they arrive on CRS-28, currently scheduled for no earlier than June 5. Four iROSA arrays are already installed and operational aboard ISS.

Since March 2009, the ISS has been equipped with 16 large solar panels on four truss elements. The original solar panels, designed to last 15 years and generate up to 240 kilowatts (kW) as a whole, have degraded over time due to the radiation environment in low Earth orbit, as expected.

The original panels on the P6 truss have lasted for just over 22 years on orbit, and, being the most degraded, were the first solar wings to be augmented by iROSA arrays. The solar panels on the S6 truss — the last truss segment to be installed on the ISS — are coming up on their 14th year on orbit, just short of their design lifetime.

Before the iROSA upgrade project started, the ISS was generating just 160 kilowatts of power, and these arrays will augment the existing solar panels, restoring the station’s power generating capacity to 215 kW. The first EVA related to the iROSA upgrade occurred in February 2021, with the first two iROSA panels — attached to power channels 2B and 4B on the P6 truss — unfurled nearly four months later.

The second pair of iROSA arrays were installed in late 2022 by Expedition 68 crewmembers Josh Cassada and Frank Rubio. These arrays are on power channels 3A and 4A on the S4 starboard and P4 port truss segments, respectively. The remaining pair of iROSA arrays will be installed on power channels 1A and 1B on the S4 and S6 starboard truss segments.

A diagram of iROSA solar array installation progress on the exterior truss segments on the ISS. This is from an earlier flight, and the 4A iROSA install is now complete. (Credit: NASA TV)

Today’s spacewalk, besides paving the way for finishing the ongoing iROSA power upgrade, also makes Wakata the fifth Japanese astronaut to walk in space. Wakata is a veteran astronaut who has flown on three different types of spacecraft across four different decades and five launches into orbit.

EVA-84 is the first US spacewalk — and the first EVA for the Station and the world — of 2023. In addition to this summer’s EVA work to finish the iROSA installation, Roscosmos has three additional EVAs planned this year to finish the ongoing project of outfitting the Nauka science module and to prepare the European Robotic Arm (ERA) for operation.

The first of these spacewalks was pushed back from its initial date in December 2022 due to the coolant leak aboard the Soyuz MS-22 spacecraft, likely caused by a micrometeoroid hit. This conclusion was the result of an analysis which showed that the hit came from a direction not favorable for orbital debris.

The European Robotic Arm is seen being controlled by cosmonaut Anna Kikina to investigate the leak on board Soyuz MS-22. (Credit: NASA TV)

EVA-84 is also the second spacewalk since that hit, and the Extravehicular Mobility Unit (EMU) suits the astronauts are using are designed to take a micrometeoroid hit of a certain size while keeping the astronaut alive long enough to get to the airlock. The EMU also has multiple layers of insulation that can slow or stop penetrating objects.

NASA spacewalk officer Kieth Johnson noted during an EVA-84 preview press conference on Jan. 17 that “If something like that were to happen, we would find out right away and start them on the path back to the airlock.” The EMU would be able to send out an emergency message, and the team on the ground would discuss the best way to take care of the astronaut.

Roscosmos is working on a forward plan for the resumption of Russian segment EVAs while also preparing Soyuz MS-23 for an uncrewed launch next month. In the meantime, Astronaut Frank Rubio’s seat liner has been transferred to the Crew Dragon Endurance should a contingency evacuation be needed before MS-23’s arrival. It is not planned to have Rubio join the Crew-5 astronauts for landing otherwise.

(Lead image: An astronaut during previous iROSA installation. Credit: NASA Johnson Space Center)

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