The grueling underwater rehearsal behind a single hour of spacewalking

Space · Published 7 October 2026 Swipe more like this →

In short: To perform a routine battery upgrade outside the International Space Station, Thomas Pesquet had to master a complex choreography of movements. Because space offers no resistance, astronauts must train in environments that mimic the physical demands of a vacuum, turning underwater pools into high-stakes rehearsal stages.

Thomas Pesquet, a French astronaut who has been aboard the International Space Station since November 19, 2016, is preparing for a critical Extra-Vehicular Activity (EVA). His primary objective is to perform maintenance outside the station to replace existing batteries with newer lithium-ion versions. This transition to more efficient power sources is a vital step in maintaining the station's long-term operational integrity.

The preparation for such a task is exhaustive, spanning months before the actual launch. Training involves a dual approach: classroom sessions at NASA’s Johnson Space Centre and intensive physical rehearsals in NASA’s Neutral Buoyancy Lab. The latter is a massive underwater facility where astronauts practice the specific movements required for spacewalks. By working in water, they can simulate the weightless environment and the physical resistance of moving heavy hardware, ensuring that every gesture is precise and safe before they face the vacuum of space.

While Pesquet focuses on his upcoming EVA, the broader Expedition 66 crew engages in a variety of related maintenance and research. Tasks involved checking the Simplified Aid for EVA Rescue (SAFER) for routine upkeep and examining the Extravehicular Mobility Unit (EMU) Scrubber Assembly to find leak sources. The SAFER device is a critical safety component designed to allow astronauts to propel themselves back to the station if they become untethered during a spacewalk. These layers of preparation—from underwater buoyancy training to hardware inspections—highlight the meticulous nature of space exploration, where a single mistake in a routine battery swap can have significant consequences.

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