The shelter order

NASA mission control instructed the four members of the SpaceX Crew-12 mission and Expedition 74 astronaut Chris Williams to enter their docked Crew Dragon spacecraft at 9:04 a.m. ET (1304 GMT) on Friday. The astronauts donned their spacesuits and remained inside the capsule, which functions as an emergency lifeboat, for approximately two hours while two Russian cosmonauts worked on the leak.

“NASA ordered all four SpaceX Crew-12 crew members and NASA astronaut Chris Williams to take elevated safety positions inside the Dragon spacecraft during the repairs.”

The order was a precautionary measure triggered by a worsening air leak in the PrK transfer tunnel near the Zvezda service module, a core structure of the Russian segment. NASA reversed the order roughly two hours later, telling the crew they could return to the station and resume normal activities.

The leak's escalation

The air leak has been a known issue for years, with cracks in the Zvezda module persisting on and off for around six years. In recent months the leak rate had been relatively minor, but it escalated on Friday from roughly one pound of air per day to two pounds (approximately 0.5 kg to 1 kg per day), according to a senior NASA official.

“The transfer tunnel of that module has been suffering cracks and leaks for some time.”

Roscosmos reported that its specialists identified two leak points. One was sealed quickly, while preparations were underway to contain the second. The Russian agency stated that at no point was there an immediate threat to the crew or the station's essential systems, and that pressure aboard the ISS remained stable.

Repair disagreements

Tensions between NASA and Roscosmos over the leak's cause and repair strategy have persisted for months. On Friday, two Russian cosmonauts — station commander Sergey Kud-Sverchkov and flight engineer Sergei Mikaev — planned to open a section of the affected area to access the crack directly. NASA officials expressed reservations about that procedure.

Roscosmos ultimately paused the repair work, and both agencies agreed to continue analysing data before taking further steps. The repair attempt followed the arrival of a Russian cargo ship last month, after which Roscosmos detected a fresh slow pressure drop in the tunnel, prompting the decision to move beyond patchwork fixes.

“We look forward to continuing to work with Roscosmos on a collaborative approach to address the leaks.”

The crew aboard

Seven astronauts are currently aboard the ISS. The Crew-12 team, which arrived in February, consists of spacecraft commander Jessica Meir (US), pilot Jack Hathaway (US), mission specialist Sophie Adenot (France, ESA), and mission specialist Andrey Fedyaev (Russia, Roscosmos). The Expedition 74 crew, which began on 8 December, includes flight engineer Chris Williams (US), commander Sergey Kud-Sverchkov (Russia), and flight engineer Sergei Mikaev (Russia).

Kud-Sverchkov and Mikaev were assigned to the repair work, with their escape route being the separately docked Soyuz MS-28 spacecraft. The five astronauts who sheltered in the Dragon were Meir, Hathaway, Adenot, Fedyaev, and Williams.

Precedent and context

The ISS has not previously required an emergency evacuation in its 25-year history of continuous habitation. The incident comes less than five months after a serious medical condition with a crew member forced NASA to bring an astronaut and three crewmates back to Earth months earlier than planned in January 2026 — the first such emergency return in the station's history.

The persistent air leak issue had already caused the postponement of a private Axiom Space mission to the station. NASA and Roscosmos continue to monitor the Zvezda module closely while assessing long-term repair options.