Mid-spacewalk, one NASA astronaut had to take a moment to show off his muscles.

What is it?

NASA astronaut Chris Williams recently left the confines of the International Space Station for a 7-hour-and-20-minute spacewalk with fellow astronaut Jessica Meir. This was Williams' second spacewalk and Meir's fifth.

In a moment of fun, Williams flexed his muscles for a photo snapped by Meir during the strenuous spacewalk. With a big grin on his face, visible even through his spacesuit helmet, Williams raised his arms in a classic Muscle Beach pose as planet Earth glowed hundreds of miles beneath him.

But the pair of astronauts weren't playing around in space; this spacewalk had a serious purpose. On June 30, Williams and Meir ventured into the void to replace a wrist joint on the space station's Canadarm2 robotic arm that had been malfunctioning.

Canadarm2 has been operating for over 25 years, so it makes sense that every once in a while it needs a repair or upgrade. After making this swap, the old wrist joint will be sent back to Earth to be fixed in case it needs to be used as backup in the future.

Why is it incredible?

Williams' demeanor in this photo makes it seem like spacewalks are fun, or even easy. But his smile and playful pose for the camera are a major contrast to the incredible strength, stamina and careful work that it takes to complete a spacewalk.

From preparation to suiting up, and doing incredibly precise work with a spacesuit on while floating in the vacuum of space while tethered to the space station, spacewalks are incredibly hard work. Williams may have been having a fun moment with Meir showing off in this photo, but the pair of astronauts were certainly using their muscles to get a tough job done.

Two NASA astronauts gave a robotic arm a hand up — or rather, a replacement wrist joint — during a successful spacewalk outside the International Space Station on Tuesday (June 30).

Chris Williams and Jessica Meir, both flight engineers on the station's Expedition 74 crew, spent seven hours and 20 minutes repairing the Canadarm2 remote manipulator system (RMS) after it was observed drawing current but not moving as expected in late May. The 58-foot-long (18 meters) arm has been in regular use since it was installed on the orbiting outpost in April 2001.

"For over 25 years, the Canadarm2 has been a crucial part of the International Space Station. The arm was key to our orbiting laboratory and continues to be a workhorse that we rely on. Whether it is performing maintenance or replacing equipment, moving and operating payloads, catching cargo vehicles or helping us out during spacewalks, the arm has played and will continue to play an essential role in our work on orbit," Williams said as the spacewalk ended.

"It is also a testament to international cooperation," he added. "Canada, the U.S. and the world have come together to make this program a success. We are honored … that we were able to give the arm a helping hand."

Williams and Meir, each wearing a NASA extravehicular mobility unit (EMU), ventured outside the Quest airlock soon after switching the spacesuits to battery power at 8:20 a.m. EDT (1220 GMT) on Tuesday. They made quick work of transitioning to their work station, where they retrieved a spare wrist joint by using a power tool (pistol grip unit) to unbolt it from an exterior equipment panel.

They then turned their focus to the arm, which was positioned nearby. They removed the old unit and installed the new joint (no. 5), bolting it in place. Williams and Meir brought the faulty joint back into the space station to be returned to Earth for analysis and possible refurbishment.

The astronauts completed their work on the arm by reattaching its latching end effector, or hand, which the arm uses to grapple objects and inchworm across the exterior of the station. Mission Control confirmed that the arm had good power connections after the astronauts' work.

Williams and Meir returned to the Quest airlock and began its depressurization at 3:40 p.m. EDT (1940 GMT), marking an end to the spacewalk.

Tuesday's EVA (extravehicular activity) marked the fourth time in history that spacewalkers have worked to service the Canadarm2. Previously, another wrist joint was replaced and both of the arm's end effectors were swapped out for spares.

"We are thrilled to have repaired the mighty Canadarm2 just in time for Canada Day tomorrow! We hope that all in Canada and everyone around the globe can celebrate this achievement," said Meir.

Expedition 74 flight engineers Jack Hathaway of NASA and Sophie Adenot of the European Space Agency assisted Williams and Meir by helping them to don and doff their spacesuits and maneuvering Canadarm2 into position for the astronauts' repair work.

This was Williams' second spacewalk and the fifth for Meir. Williams has now logged 14 hours and 22 minutes, including a previous EVA with Meir. Meir has totaled 36 hours and 6 minutes, including the first all-female EVA in 2019.

Tuesday's spacewalk was the 280th in support of International Space Station assembly, maintenance, and upgrades since 1998.

One of the space station's robot arms, crucial for catching cargo ships and doing a share of maintenance duties, is offline for at least a few weeks for repairs.

Canadarm2, which just passed 25 years of service in April on the International Space Station (ISS), will require a spacewalk to fix an apparently broken part that seized up during routine work on May 27, NASA said in a blog post Wednesday (June 10).

The arm is in a stable spot, but it is awaiting help from spacewalking astronauts on June 30 — the day before Canada Day, a national holiday in that country. "The system demonstrated an elevated motor current in a wrist joint, and arm motion did not occur as expected," NASA officials wrote of the issue. Consultation with the Canadian Space Agency (CSA), which funds the arm and supports its operations with MDA Space, showed a spacewalk will be needed to replace the affected joint. Luckily, a spare is already on station.

"Canadarm2 was designed with these kinds of potential issues in mind: it is made up of several segments that can be pulled out and replaced in space," the CSA wrote in a Wednesday update on its website. "Knowing that parts would eventually have to be replaced, the CSA planned shipments of key spares to the station well in advance. In 2017, a similar repair happened with one of the robotic arm's 'hands' after it started to show signs of normal wear and tear."

NASA plans a news conference at a to-be-announced date to discuss the spacewalk and to share more about the assigned spacewalkers. The two astronauts will likely be drawn from the Expedition 74 crew on the U.S. side of the station, which include NASA's Chris Williams, Jessica Meir and Jack Hathaway, and the European Space Agency's Sophie Adenot.

Getting Canadarm2 back online will be critical to berth some cargo ships at the space station, which carry food, equipment and other supplies to the astronauts, as well as to perform a share of maintenance on the orbiting complex. The last Canadarm2 berthing took place in April with Williams controlling the arm, and Hathaway supporting, to pick up the arriving Northrop Grumman Cygnus XL spacecraft.

Notably, Canadarm2 was not originally designed for ship arrivals (it flew to station in 2001, long before the rise of commercial spacecraft), but it made a milestone 50th "cosmic catch" in 2024 and has kept going despite being now 10 years past its design life as of this year.

Moreover, tasks over the decades have increasingly transferred to the ground, both at NASA in Houston and at the CSA headquarters near Montreal, Quebec. Controllers in Canada alone support more than 100 days of work a year for Canadarm2 and other Canadian ISS robotics (including the Dextre "hand"), which includes picking up equipment, transferring experiments, and performing other duties that don't require precious astronaut time.

The CSA's robotics on station represent its share of the ISS funding arrangement, allowing CSA astronauts and science to fly. The next CSA astronaut to go there will be Josh Kutryk, flying aboard SpaceX Crew-13 no earlier than September; the last was David Saint-Jacques in 2018-19.

Canadarm2 forms part of a long line of Canadian space robotic arms, originating in part with Canada's National Research Council technology that underlay early satellite antennas and the "legs" of Apollo lunar landers.

The first Canadarm made its debut flight on the second space shuttle mission in 1981. Canadarm2 helped build the ISS and supports station activities, and Canadarm3 is a next-generation arm being constructed to support the Artemis program, which saw CSA astronaut Jeremy Hansen fly around the moon on Artemis 2 in April.

One of Canadarm2's biggest moments in history was a near-emergency repair of a torn solar array in 2007, which required NASA spacewalker Scott Parzaynski to ride on the arm and a Canadian robotic "boom" extension to reach the faraway, live solar panel part for a fix.

The S.S. Steven R. Nagel has arrived at the International Space Station.

The second of Northrop Grumman's Cygnus XL cargo spacecraft to deliver supplies to the orbiting outpost, the vehicle was captured by the space station's Canadarm2 robotic arm at 1:20 p.m. EDT (1720 GMT) on Monday (April 13).

"Cygnus capture is complete," radioed Chris Williams, a NASA astronaut and Expedition 74 flight engineer, to Mission Control. "The S.S. Steven Nagel, welcome aboard the ISS!"

Williams was at the controls of the arm when the spaceship was grappled. Assisting him was fellow NASA ast Jack Hathaway. Flight controllers on the ground will next take control of the arm to berth the Cygnus on the Earth-facing port of the station's Unity Node 1 for unloading.

On board the S.S. Steven R. Nagel, which was named for a late space shuttle-era astronaut, are about 11,000 pounds (5,000 kg) of science equipment and logistics for the Expedition 74 crew. Among the specific research studies being delivered are quantum science module that could advance the hunt for dark matter, as well as improve computing technology and the equipment needed to increase therapeutic stem cell production to treat cancer and blood diseases.

Cygnus is also carrying a gut microbiome study and a receiver that could help protect space-based GPS and radar systems by improving our ability to predict space weather.

Launched on a SpaceX Falcon 9 rocket from Florida on Saturday (April 11), the S.S. Steven R. Nagel is scheduled to stay attached to the space station until October. The flight is Northrop Grumman's 24th under NASA's Commercial Resupply Services (CRS-24) contract.

Robot, meet spacecraft.

A new video shows what it's like to capture a visiting cargo ship at the International Space Station (ISS) — specifically, a Northrop Grumman Cygnus vehicle, which arrived Feb. 1 with vital supplies for the Expedition 70 crew.

NASA astronauts Jasmin Moghbeli and Loral O'Hara worked together at the controls of the Canadarm2 robot arm, in the ISS wraparound Cupola window, to make the cosmic catch. Moghbeli posted the footage on X, formerly Twitter, on Feb. 13.

Related: Private Cygnus cargo ship arrives at the ISS carrying 8,200 pounds of supplies

Canadarm2 is the second generation of robot arm from the Canadian Space Agency (CSA) and is now managed by supplier MDA. First used in the space shuttle program, the Canadarm series has assisted on spacewalks, hefted space station modules, repeatedly released and scooped up the Hubble Space Telescope, and performed many other tasks besides.

First installed on the ISS in 2001 by CSA astronaut Chris Hadfield and NASA astronaut Scott Parazynski, Canadarm2 was joined by a robotic helper named Dextre in 2008. Dextre specializes in moving smaller things around that require more dexterity. 

Canadarm2 was not exactly designed for berthing space station ships. But it has proved so capable that it has done dozens of these captures since May 2012, when a SpaceX Dragon cargo ship arrived at the ISS for the first time.

CSA and MDA are both working on successor robotic technology, called Canadarm3. This arm — complete with a large limb, a small limb and a "backpack" that can carry supplies around — will be mounted on NASA's moon-orbiting Gateway station, which the agency aims to start assembling in the next few years. 

CSA brokers seats and science on the ISS and NASA's Artemis moon program using its Canadarm series. Canadarm3 funded astronaut Jeremy Hansen's seat aboard the round-the-moon mission Artemis 2, for example, that should fly in 2025 or so. The next CSA astronaut on ISS will be Joshua Kutryk, also in 2025.

This space wallpaper reveals, with clouds and land forming a backdrop, the SpaceX Dragon commercial cargo craft is grappled by the Canadarm2 robotic arm at the International Space Station. Expedition 31 Flight Engineers Don Pettit and Andre Kuipers grappled Dragon at 9:56 a.m. (EDT) and used the robotic arm to berth Dragon to the Earth-facing side of the station's Harmony node at 12:02 p.m.