Astronauts on board the International Space Station were ordered to prepare for a possible evacuation during attempts to fix a worsening air leak on Friday.
Five members were directed by Nasa’s mission control to take refuge in their docked spacecraft in case they needed to escape quickly as repairs were carried out by a Russian crew on a transfer tunnel, which has suffered from cracking.
They were also told to put on their spacesuits.
However, the rare safe-haven procedure was ended about two hours later and the astronauts returned to the football pitch-sized laboratory, orbiting 400km above the Earth.
Fractures in the Zvezda service module had been a continuing concern, said Nasa.
The agency has been working with its Moscow-based counterpart Roscosmos to find the root cause of the problem, which has been managed through mitigation measures and partial repairs.
Announcing the precautionary measure, Nasa spokeswoman Bethany Stevens said in a post on X said cracks on the Zvezda "have always been a concern that Nasa watches very closely".
Roscosmos said its experts had found two leaks on board the ISS but steps had been taken to address these.
“The situation does not threaten the safety of the crew and on-board systems – the pressure on board the ISS is stable and maintained at the calculated level,” the agency said.
There are currently seven astronauts on board the station.
