ESA/NASA astronauts begin installation of new solar arrays on ISS -

Two astronauts have ventured outside the International Space Station (ISS) to install the first of six new solar arrays — part of a program to increase the station’s electrical power generation capacity as its science and research demands increase and future expansion plans continue.

The Extravehicular Activity (EVA) – officially known as US EVA-74 – began at 12:11 UTC / 08:11 EDT when Thomas Pesquet from the European Space Agency (ESA) and Shane Kimbrough from NASA took their spacesuits to battery power before exiting the Quest Airlock to begin their work.

IROSA background

The eight original Solar Array Wings (SAWs) on the ISS, which each produce around 30 kilowatts (kW) of power for a total of about 250kW are beginning to show signs of degradation, with the oldest array now having been in space since 2000 when the P6 truss and associated arrays was delivered to the station by Shuttle Endeavour’s STS-97 crew.

With over 20 years of use, and normal degradation of solar arrays, the eight SAWs now only produce around 160kW of power – against a backdrop of rising power demands from the station’s increasing users.

This led the Station program to develop the ISS Power Augmentation (IPA) plan, which called for adding six additional solar arrays to the station in order to restore the outpost’s power generation to its original levels.

Under the IPA program, six new ISS Roll Out Solar Arrays (IROSAs) will be added. Whilst the station’s original arrays were folded up and deployed in an accordion-like manner, the IROSAs are a new type of array technology which roll out in a mat-like manner from inside a cylindrical canister.

The IROSAs will be installed on top of six of the station’s existing solar arrays, which will allow the IROSAs to utilize the same sun-tracking motors and be connected into the same electrical system as the current arrays.

With the IROSAs being around 30% efficient, compared to the 14% efficiency of the original arrays, the IROSAs will generate roughly the same amount of power as the originals despite being only half their size.

Each IROSA will produce 20kW of additional power, for a total of 120kW across all six arrays.  

However, because the IROSAs are smaller, they will not completely cover the half of the six SAWs they’ll be installed over. Instead, portions of the original arrays will still be power positive. 

The unshadowed portions of the original arrays will continue to produce 95kW as a result, making for a combined total of 215kW of power available to the ISS — an increase of nearly a third compared with the outpost’s current levels.

👨‍🚀👨‍🚀 @astro_kimbrough and I will be heading out soon, to install some solar panels ☀. @NASA has been preparing for these spacewalks for over 1.5 years, the instructions span 28 pages, it is astounding what humans can do with teamwork. See you later! 👋

— Thomas Pesquet (@Thom_astro) June 16, 2021

This first IROSA was launched along with the second aboard the SpaceX CRS-22 cargo Dragon mission that launched from Florida back on 3 June.  The second IROSA — assuming the first

EVA today goes to plan — will be installed during a following spacewalk currently scheduled for Sunday, 20 June.

EVA procedures

For EVA-74, ESA astronaut Thomas Pesquet is EV1 while NASA astronaut Shane Kimbrough is EV2.

After exiting the Quest Airlock, the first task for the pair will be to translate out to the IROSA Flight Support Equipment (FSE).

The FSE is a pallet on which the pair of IROSAs are attached, and it was removed from cargo Dragon’s trunk by Canadarm2, also known officially as the Space Station Remote Manipulator System (SSRMS) — part of the overall Mobile Base System on the station.

Canadarm3 then installed the FSE onto the Mobile Base System (MBS) Payload ORU Accommodation (POA).

For Pesquet and Kimbrough, after translating to the FSE, the duo will begin setup of the worksite and release launch restraint bolts on the IROSA, with Kimbrough then translating out to the P6 truss installation site — specifically the 2B Integrated Electronics Assembly (IEA) — to begin more setup.

Once complete, bolts will be turned to release the IROSA from the FSE, and Pesquet – mounted to the end of Canadarm3 – will hold on to the IROSA while he is “flown” out toward the P6 truss.

Inside the ISS in the Robotics Work Station in the Cupola viewing module, NASA astronaut Megan McArthur will be at the controls of Canadarm3; she will be the one to physically drive Pesquet out toward the P6 truss.

However, due to the fact that P6 is at the very outboard end of the station, Canadarm3 cannot reach all the way to the worksite, meaning Pesquet will have to hand-off the IROSA to Kimbrough, who will in turn hold on to it whilst Pesquet dismounts the arm and repositions.

ESA/NASA astronauts begin installation of new solar arrays on ISS -

Angle showing how the new IROSAs will be deployed over the current arrays. (Credit: NASA)

Once Pesquet is in position, Kimbrough will hand the IROSA back to him. The duo will then align the IROSA onto the mounting bracket of the “Mod Kit” — which was installed during a spacewalk earlier this year — at the base of the 2B Mast Canister Assembly (MCA).

The IROSA will first be soft-docked onto the mounting bracket before being unfolded into its deployment configuration. Eight bolts will then be driven to hard mount the IROSA onto the bracket.

Four electrical connections will then be mated between the IROSA and the 2B MCA in order to connect the IROSA into the electrical system of the current 2B solar array.

Two bolts will then be driven to begin the roughly six-minute IROSA deployment sequence – which will mechanically unroll itself with no electrical actuators required. Once fully deployed, Pesquet and Kimbrough will drive two tensioning bolts to increase the rigidity of the array, which will complete the installation of the 4B IROSA.

ESA/NASA astronauts begin installation of new solar arrays on ISS -

The ISS once the new arrays are installed – via Mack Crawford for NSF L2.

The duo will then prepare the neighboring 4B worksite for the installation of a second IROSA on the following EVA before heading back inside the Quest airlock to conclude the EVA. As with its start, the EVA will be marked complete when Pesquet and Kimbrough take their suits off battery power.

Overall, this is the 239th EVA in support of Station construction and maintenance and the seventh spacewalk so far this year outside the outpost.

(Lead image: Placement of the new IROSAs over the existing Station solar arrays. Credit: Mack Crawford for NSF L2)