NASA terminated a spacewalk on Friday following a possible leak in US astronaut Tim Kopra's spacesuit. The six-and-a-half-hour spacewalk mission to replace an electrical component in ISS' solar power system was cut short after little under five hours due to a water bubble formation in Kopra's helmet.

The main objective of the spacewalk carried out by NASA's Kopra and ESA (European Space Agency) astronaut Tim Peake, which lasted for four hours and 43 minutes, was to replace a failed voltage regulator that caused one of the eight ISS' power channels to shut down last November. The primary task at hand was accomplished before the crew returned to the airlock for the inspection of the water bubble formation in Kopra's helmet.

Commander Rob Navias said in a live broadcast on NASA TV that both astronauts were "not in any danger whatsoever", adding that the early termination was a precautionary measure, according to Business Insider.

The International Space Station reported that spacewalkers safely returned to the airlock at 12:31pm ET. The fellow crew members along with Commander Scott Kelly helped Kopra out of the spacesuit and collected the water sample to determine the cause of the leak, according to NASA.

NASA astronaut Douglas Wheelock, who was answering queries on Twitter under hashtag #askNASA, said the crew reported the water found in Kopra's helmet was cold, which indicated a leak in the suit's cooling system.

Peake, the 43-year-old army major who left on a six-month mission to the ISS for the ESA in December, became the first British citizen to walk in space. As for Kopra, it was his third expedition.

The flight rules for astronauts on spacewalks were tightened after an incident in July 2013 that nearly caused Italian astronaut Luca Parmitano to drown. The leak in Parmitano's helmet was a lot worse than Kopra's. According to NASA, 1-1.5 liters of water had entered Parmitano's helmet, covering his ears, eyes, nose, part of his mouth that caused impaired visibility and difficulty in breathing.

"I experienced what it's like to be a goldfish in a fishbowl from the point of view of the goldfish," Parmitano said in a video posted on sharing his near-drowning experience. "It was really hard to communicate. I went back just using memory...going back to the airlock."