Two astronauts have aborted their spacewalk and hurried back into the International Space Station after water leaked into one of the men's helmets in a scary repeat of a near drowning 2 1/2 years ago.
The trouble cropped up after the astronauts - including Britain's first spacewalker - successfully restored full power to the space station on Friday.
NASA astronaut Timothy Kopra caused concern when he reported a small water bubble and then a film of water inside his helmet.
Mindful of another spacewalker's close call in 2013, Mission Control terminated the planned six-hour spacewalk at the four-hour mark. It turns out Kopra was wearing the same spacesuit involved in the earlier incident.
"So far, I'm OK," Kopra assured everyone. Later he said the water bubble was 10cm long and getting thicker.
Lead flight director Royce Renfrew, who called an early end to the spacewalk, stressed the situation was not an emergency and insisted neither spacewalker was in danger.
An hour later, Kopra was safely inside his orbiting home, along with Timothy Peake, who attracted his own headlines by becoming Britain's first spacewalker on Friday.
The astronauts waiting anxiously inside pulled off Kopra's helmet, then measured the water that had leaked, presumably from the suit's cooling system. That was the source of the leak last time. Space station commander Scott Kelly reported he filled a syringe with about 1cu cm of water.
NASA officials said more than a litre of water escaped into the helmet and suit of Italian astronaut Luca Parmitano in July 2013.
Kopra's suit was the same one Parmitano was wearing when his helmet flooded. The suit was refurbished following the 2013 incident. NASA said Kopra used the same suit for a spacewalk last month without any problem, and it had been used previously as well.
Despite the latest leak being smaller, the cap Kopra wore under his helmet was moist, as were other parts of his suit.
Kopra and Peake completed their No.1 job early in the spacewalk. They quickly removed the voltage regulator that failed two months ago, slashing station power by one-eighth. The breakdown did not disrupt work 400km up, but NASA wanted the power grid fixed as soon as possible in case something else failed.
Working in darkness to avoid electrical shock from the solar power system, the astronauts removed the bad unit and popped in a spare, both about the size of a 113-litre aquarium. They had just 31 minutes, the amount of nighttime on that particular swing around the world, to complete the job.
Mission Control said the spare - dubbed Dusty for its 17-year tenure in orbit - appeared to be working properly.
Engineers suspect the original electronic unit suffered an internal electrical short. In the meantime, the station relied on seven other power channels.
Peake received a bounty of well wishes as he became the first spacewalker to wear the Union Jack on his suit.
"We're all watching, no pressure!" former Beatle Sir Paul McCartney said via Twitter. "Wishing you a happy stroll outdoors in the universe."
As Peake floated out, space station commander Scott Kelly called, "Hey Tim, it's really cool seeing that Union Jack go outside. It's explored all over the world. Now it's explored space."
Replied Peake: "It's great to be wearing it, a huge privilege, a proud moment."
Peake is a helicopter pilot and was chosen by the European Space Agency.
Engineers will scour data in the weeks ahead to figure out what happened with the suit and helmet.
Parmitano was at the European Astronaut Centre in Cologne, Germany, during Friday's spacewalk, answering questions about spacewalking.
