Astronauts Step Outside to Swap Batteries on the ISS

Today NASA astronauts Chris Cassidy and Bob Behnken suited up and headed out the airlock for a spacewalk with a very unglamorous but essential job: swapping out batteries on the space station’s exterior truss. Out with the old nickel-hydrogen batteries, in with newer lithium-ion ones.

It’s not the kind of spacewalk that makes for dramatic headlines, but it’s exactly the sort of maintenance that keeps a two-decade-old orbiting laboratory running. The ISS truss carries the solar array power channels, and those batteries store the energy the station collects from the sun so systems keep humming through the roughly 45 minutes of every 90-minute orbit spent in Earth’s shadow. Nickel-hydrogen batteries have done the job since the station’s solar arrays went up, but they’re heavy and their capacity fades. Lithium-ion cells pack more energy storage into less mass, which is why NASA has been steadily working through this upgrade across multiple spacewalks over the past couple of years.

Behnken’s busy stretch outside

What’s notable about today’s excursion is that it’s the fourth spacewalk Bob Behnken has performed during his stay aboard the station — a stay that’s part of SpaceX’s Demo-2 mission, the first crewed test flight of the Crew Dragon capsule. Behnken and fellow astronaut Doug Hurley rode Dragon up to the ISS back in May, and Behnken has clearly been earning his keep since arriving, cycling through EVAs at a pace that’s unusual for a roughly two-month stay. Four spacewalks in that window is a lot of suit-up-and-go-outside time, and it says something about both the workload NASA had queued up and Behnken’s experience as a veteran spacewalker from his shuttle days.

Cassidy, for his part, is the station’s current commander and has now logged multiple EVAs of his own during this expedition. Pairing him with Behnken for battery work makes sense — this isn’t first-time-outside kind of task, it’s methodical, checklist-driven hardware swapping where experience pays off in efficiency and safety.

Battery replacement EVAs follow a well-worn choreography at this point: astronauts translate out along the truss, disconnect the old units, install adapter plates if needed, wire in the new lithium-ion batteries, and verify everything talks to the station’s power system before heading back inside. It sounds almost routine written out like that, but every minute outside in a pressurized suit, tethered to a spacecraft moving at 17,500 miles an hour, carries real risk. That’s part of why these missions get planned down to the minute and rehearsed extensively on the ground beforehand.

There’s also a nice bit of symmetry to this spacewalk given the Demo-2 backdrop. Dragon’s whole purpose is to restore an American ability to launch crew from home soil rather than relying solely on Soyuz seats, and here you have a Demo-2 crew member out doing genuine station upkeep, not just riding along as a test-flight passenger. It underscores that once astronauts get to orbit, the actual work of keeping the ISS alive doesn’t care which capsule brought them there.

With this battery swap complete, expect NASA to keep chipping away at the remaining nickel-hydrogen units on other truss segments in future EVAs. It’s slow, steady infrastructure work — the kind that rarely trends online but is exactly what keeps humans living and working in orbit reliably.