The first official British astronaut to walk in space, Tim Peake, said it was "a privilege" to wear the Union flag on his space suit as he left the International Space Station (ISS) on a maintenance operation.
Major Peake, 43, from Chichester, West Sussex, is on a six-month mission with the European Space Agency and today embarked on his first Extra-Vehicular Activity (EVA) - or spacewalk - making history in the process.
The six-and-a-half hour venture, which began just before 1pm on Friday, allowed Major Peake and his Nasa colleague Colonel Tim Kopra, 52, to repair a broken voltage regulator box that failed in November.
As Major Peake left the space station, sporting the Union flag on his shoulder, his colleague Commander Scott Kelly took a moment to point out the significance of the moment.
Mr Kelly said: "The Union Jack has explored all over the world, now it's exploring space."
Major Peake replied: "It's great to be wearing it. A privilege, a proud moment."
The historic moment was broadcast to millions back on Earth via a live stream on the Nasa web site.
In Westbourne, Emsworth, Hampshire, Major Peake's parents, Nigel and Angela Peake, beamed with pride as they watched their son's progress from their living room.
Mr Peake said: "It's amazing, the photographs from space are incredible.
"For us, we have immense pride, but also immense gratitude to all the people who are supporting Tim and the other astronauts."
Rebecca Peake, Major Peake's wife, left a short message for her husband as he left the ISS.
Using a screen grab from his helmet camera, she wrote on Twitter: "@astro_timpeake thank you for taking our boys with you into the vacuum of space".
The astronaut also received messages from Prime Minister David Cameron, who earlier posted: "Good luck to @astro_timpeake on today's #spacewalk. The country will be watching you make history #ScienceIsGREAT"
Celebrity well-wishers included Sir Paul McCartney, who added: "We're all watching, no pressure! Wishing you a happy stroll outdoors in the universe."
Guided by ground staff in Houston, the pair successfully replaced the broken power box with a spare unit. They inspected the broken equipment and found no damage, meaning the fault was likely internal.
Since the box broke in November, the ISS has been operating unaffected using the remaining seven power units.
Major Peake and his colleague are working in challenging conditions, with 45-minute blocks alternating between sunlight and complete darkness, and are having to fight the pressure of their space suits over more than six hours. They have water to drink from pouches and cannot stop for any toilet break.
But they have trained for years for the career-defining experience, including in the world's largest swimming pool, and the entire operation has been timed and planned to the minute. The pair studied a 40-page document outlining what will happen in every stage of the operation.
The astronauts are performing a number of other maintenance tasks before they head back inside the ISS.
Once they return, their colleagues inside the station will help with a 25-minute clean-up and further checks.
Only then will they be able to get out of their suits and adjust to the pressure back in the station.
Major Peake, a former Army Air Corps and helicopter test pilot, is the first Briton aboard the ISS and the first fully British professional astronaut employed by a space agency.
Previous "Brits in space" have either had US or dual citizenship or been on privately funded or sponsored trips.
He arrived at the station on December 15.