Astronauts aboard the International Space Station were ordered to prepare for a potential evacuation, as engineers worked to fix a worsening air leak.
Five crew members were instructed by Nasa’s mission control to retreat to their docked spacecraft, ready for a swift departure, while a Russian team repaired a cracked transfer tunnel.
They were also told to don their spacesuits.
However, the rare “safe haven” protocol was stood down approximately two hours later, allowing the astronauts to return to the football-pitch-sized laboratory, orbiting some 250 miles above Earth.
Fractures in the Zvezda service module had been an ongoing 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 spokesperson Bethany Stevens said in a post on X: “The Zvezda service module transfer tunnel, known as PrK, has suffered from cracks and leaks for some time, and has been mitigated by Roscosmos as much as possible to date. The cracks have always been a concern that Nasa watches very closely.
“Nasa and Roscosmos have been working to determine the root cause of the cracks, and Roscosmos manages the issue through operational mitigation measures and periodic partial-repair efforts.
“Following new leaks, Roscosmos has elected to proceed with a more extensive repair operation on Friday June 5.
“Out of an abundance of caution, Nasa has directed all four of the agency’s SpaceX Crew-12 members and Nasa astronaut Chris Williams to assume an elevated safety posture in the Dragon spacecraft while the repair is under way.
“We continue to work with our Russian counterparts, along with the rest of the international community that supports the space station, to arrive at a more permanent resolution.”
In a later update, she added: “Roscosmos has paused Friday’s structural repair efforts inside the Zvezda service module transfer tunnel, known as PrK, as more measurements and data is assessed.
“Given this development, Nasa has instructed the crew members inside the Dragon spacecraft to end the safe haven procedures and return to planned operations aboard the International Space Station.
“We look forward to working with Roscosmos on a collaborative approach to address the leaks.”
Roscosmos said its experts had found two leaks on board the ISS but steps had been taken to address these.
In a statement, the agency said: “The situation does not threaten the safety of the crew and onboard systems – the pressure on board the ISS is stable and maintained at the calculated level.”
There are currently seven astronauts on board the station.
