Astronauts Koichi Wakata and Nicole Mann have completed another spacewalk, continuing work to enable the final set of upgraded ISS Roll-Out Solar Array (iROSA) “solar wings” to be installed on ISS sometime this summer.
Following US EVA-84 on Friday, Jan. 20, Wakata and Mann conducted US EVA-85 on Thursday, Feb. 2.
On Friday, Jan. 20, at 7:14 AM CST (13:14 UTC), the astronauts left the Quest airlock module on US EVA-84. Koichi Wakataa, EV1, wore the suit with the red stripes while Nicole Mann, EV2, wore the suit with no stripes. This was the first spacewalk for both astronauts, and they used EMUs 3004 and 3009.
The first task for Wakata was to torque two collar bolts, M25 and M26, to 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 was done with this task on the S6 truss, he translated over to the S4 truss and worked with Mann on the iROSA kit installation for the 1A power channel. They installed a triangular fitting on top of the Beta Gimbal Assembly (BGA), then attempted to install four trusses, two on each side of the triangular mount before torquing the bolts to finish the truss installation.
Issues installing the fourth such strut prevented the completion of the bracket install and precluded other tasks originally planned for EVA-84. Mann’s next task was 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 was then to complete the iROSA mounting installation for this EVA by routing cables to his side of the mounting bracket.
Mann was then to 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.
Possible get-ahead tasks also planned for EVA-84 involved 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 was considered was the retrieval for refurbishment of a robotic micro conical tool stored on the ISS exterior.
The astronauts left the Quest airlock again at 7:42 AM EST (12:42 UTC) on Thursday, Feb. 2 to begin EVA-85. Mann served as EV1, using EMU 3009 and wearing the red-striped spacesuit. Wakata wore the unmarked suit and used EMU 3004 as EV2.
The EVA began by troubleshooting the problematic strut from EVA-84. After a few failed attempts to attach the final strut, the truss was successfully completed.
Mann and Wakata then moved ahead to begin deploying power cables also originally planned for EVA-84, as well as relocating a foot restraint for future spacewalks.
These were the final tasks finished before the spacewalk concluded at 2:26 PM EST (19:26 UTC).
ISS Roll-Out Solar Arrays
Following EVAs 84 and 85, the way is 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.
The latest spacewalks, 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.
EVAs 84 and 85 are the first US spacewalks — and the first EVAs 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 that showed that the hit came from a direction not favorable for orbital debris.
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.