Pallab Ghosh
Science correspondent

If the air leak in the Zvezda service module continues to worsen, the ISS crew has a clear emergency exit plan — but it involves splitting up across two separate spacecraft.

Five of the seven crew members are currently sheltering inside the docked SpaceX Crew Dragon "Freedom" spacecraft as a precautionary measure.

Nasa has directed Crew-12 astronauts Jessica Meir, Jack Hathaway, Sophie Adenot and Andrey Fedyaev to take refuge there, along with Nasa astronaut Chris Williams.

They have been told to put on their spacesuits so they are ready to undock and return to Earth at short notice. The Dragon effectively functions as a lifeboat — attached to the station but ready to detach the moment the order is given.

The two Russian cosmonauts, station commander Sergey Kud-Sverchkov and flight engineer Sergei Mikaev, are in a different position entirely.

They remain in the Russian segment - closest to the leak - carrying out the repair work. Their escape route is the separately docked Soyuz MS-28 spacecraft.

However, in a full evacuation, the crew would not simply leave on whichever vehicle they are currently sheltering in.

Crew members are assigned to specific return vehicles before they ever launch.

That means Dragon would carry the four Crew-12 members - Meir, Hathaway, Adenot and Fedyaev - splashing down off the US coast, while Kud-Sverchkov, Mikaev and Williams, all of whom launched together aboard Soyuz MS-28 last November, would make a separate landing on the Kazakh steppe.

For now, Nasa is emphasising this is a precautionary measure, not a full evacuation order. The agency says it is monitoring the situation closely and working with Roscosmos on a more permanent fix. But with suits on and engines ready, the crew is prepared to leave at a moment's notice.