NASA cut short a spacewalk on Friday at the International Space Station after one of the astronauts reported a possible leak in his spacesuit helmet.
Tim Peake, who on the mission became the first astronaut from Britain to walk in space, and US astronaut Tim Kopra, had finished the primary goal of their outing when Mr Kopra reported a water bubble had formed in his helmet.
“The crew is not in any danger whatsoever,” mission commentator Rob Navias said in a live broadcast of the spacewalk on NASA TV.
Ending the spacewalk two hours early was a precaution, Mr Navias added.
NASA tightened its flight rules after a spacesuit worn by Italian astronaut Luca Parmitano leaked during a spacewalk in July 2013, nearly causing him to drown.
Mr Kopra, who was making his third spacewalk, and Mr Peake had replaced a failed voltage regulator in the station's power system shortly after leaving the station's airlock at around 1pm (irish time).
They were scheduled to spend more than six hours outside the station, a $100 billion research laboratory that flies about 400km above Earth, on other maintenance chores.
That work will be rescheduled, Mr Navias said.
Mr Peake, (43), a former army major, blasted off to the ISS as part of a six-month mission for the European Space Agency in December, becoming the first Briton in space since Helen Sharman travelled on a Soviet spacecraft for eight days in 1991, and the first to do so under a British flag.