Astronaut Tim Peake on Friday became the first Briton to walk in space, undertaking a tricky mission in the dark to replace an electrical unit.

Peake and US colleague Tim Kopra switched their spacesuits to battery power at 1248 GMT, marking the official start of the floating maneuver for Peake, who is also the first British astronaut to fly to the orbiting International Space Station.

As Peake climbed out of the space station, American astronaut Scott Kelly positioned a camera from inside so that the British flag on the arm of Peake’s spacesuit was visible to viewers watching live on NASA television.

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“Great to see the Union flag out there,” said Kelly.

“It’s great to be wearing it,” answered Peake. “It’s a privilege.”

The 43-year-old Peake’s first job was to haul a bulky component called a sequential shunt unit, contained in a white bag as big as a suitcase.

He carried the unit, which would weigh 200 pounds (90 kilograms) on Earth, to the far end of the space station’s truss, about 200 feet (60 meters) from the exit.

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The replacement voltage regulator unit is nicknamed “Dusty,” because it arrived on the space station back in 1999, said NASA commentator Rob Navias.

Kopra, 52, making his third career spacewalk, toted the tools needed to remove the old unit and replace it with the new one.

The team’s work was precisely timed to coincide with a nighttime pass of the space station to avoid sparks from any residual electrical current in the solar-powered equipment.

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The ISS circles the Earth every 90 minutes, spending 31 of those minutes on each pass in the dark.

The first portion of the nighttime job began at 1437 GMT and was finished about 20 minutes later.

“Everything is going swimmingly,” Navias said.

Next, the astronauts will route cable and install a vent in a cramped space that spacewalk officer Paul Dum described this week as a “challenging work site.”

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- ‘No pressure’ -

In a blog post on Thursday, Peake said he felt “exhilarated” but had “no time to dwell on these emotions.”

Peake said he had spent months on Earth training for the mission, including virtual-reality sessions to prepare “for the worst-case scenario of becoming detached from the space station.”

Each step of the six-and-a-half hour spacewalk was “meticulously planned,” he added.

“But I guess nothing can prepare for the feeling of being outside of a spacecraft in the vacuum of space.”

As the first British person to reach the ISS — following the first British citizen in space, Helen Sharman, who flew to the Russian Mir space station in 1991 — Peake has drawn plenty of attention from his compatriots.

Among them was the Beatles legend Paul McCartney, who offered a message of “good luck” on Twitter.

“We’re all watching, no pressure! Wishing you a happy stroll outdoors in the universe,” McCartney wrote.