British astronaut Tim Peake will say goodbye on Saturday to the space station that has been his home for the past six months and return to Earth.
A Soyuz space capsule carrying the 44-year-old former helicopter test pilot is due to land on a remote spot on the Kazakhstan steppe at around 10.15am, UK time.
With him will be Principia mission crewmates, US Nasa astronaut Colonel Tim Kopra and Russian cosmonaut Yuri Malenchenko.
Shortly after 3am, the three men will scramble from the International Space Station (ISS) to the Soyuz TMA-19M spacecraft that took them into orbit on December 15 last year.
Closing the hatch will mark the official end of Major Peake's historic mission, which earned him an honour from the Queen for "extraordinary service beyond our planet".
Major Peake was the first British astronaut to be sent to the ISS by the European Space Agency (Esa).
The father-of-two took part in more than 250 experiments, performed a space walk, ran the London Marathon on a treadmill, and inspired more than a million schoolchildren.
The trip home involves a hair-raising plunge through the atmosphere in the tiny middle section of the Soyuz, the descent module.
Friction on the spacecraft's heat shield will slow its speed from 17,398 mph (28,000 kph) to 514 mph (827 kph) and raise the outside temperature to 1,600C.
The rapid deceleration will push the crew back into their shock-absorbing seats with a force of around five gee - five times normal Earth gravity.
One Nasa astronaut, Doug Wheelock, has described the experience of a Soyuz descent as "like going over Niagara falls in a barrel, but the barrel is on fire".
If all goes according to plan, the return to Earth will be controlled automatically by the craft's on-board computer. In an emergency, the crew, led by commander Malenchenko, can alter their trajectory manually using a hand controller.
The capsule is expected to land in a remote location on flat steppe scrubland more than 200 miles from the major Kazakhstan city of Karaganda.
Fifteen minutes before landing, four parachutes will be deployed in succession. One second before touchdown, retro rockets will fire and the spacecraft will hit the ground at 3mph.
Rescue crews will rapidly arrive at the site to help the space travellers out of their capsule and take them for medical checks.
They will be helicoptered to Karaganda airport, where according to tradition they will be offered bread and salt and a traditional Kazak hat.
Major Peake will then be flown to the European Astronaut Centre in Cologne, Germany, while his American and Russian colleagues go their separate ways to Houston and Star City, near Moscow.
His mission was named Principia after Sir Isaac Newton's landmark work describing the laws of motion and gravity.
Its primary purpose was to contribute to scientific knowledge by conducting experiments in zero gravity.
But the British astronaut did much more than that as he constantly kept in touch with the world by Twitter, took part in video-linked Q&A sessions, and engaged in educational activities that reached more than a million schoolchildren.
His success in putting Britain on the space-faring map earned him a unique place in the Queen's Birthday Honours list.
Becoming the first person to be honoured while in space, he was made a Companion of the Order of St Michael and St George for "extraordinary service beyond our planet".
Speaking from the ISS he said his space walk, conducted with Col Kopra in January to repair electrical components, was the highlight of his mission.
He added that he was looking forward to "private time" with his family, fresh air, and the feeling of raindrops on his face.
During his time in space Major Peake worked up to 14 hours a day, participating in more than 250 experiments devised by scientists from around the world.
They included numerous studies of his own body's responses to the space environment involving his brain, lungs, stomach, muscles, bones, skin, immune system and body clock.
The tests will continue as he begins a lengthy process of rehabilitation back on Earth.
While weakened muscles recover quickly after a long spell in space, it can take up to three years for bones to return to normal.
Despite their strict exercise regime, astronauts on average lose up to 1.5% of their bone mass for each month spent in space.
Major Peake was originally scheduled to return at the beginning of June, but his homecoming was delayed when the launch of the replacement crew was pushed back.