Astronaut Tim Peake is counting down to the London Marathon, which he will run on board the International Space Station in just 11 days' time.
The Briton faces a lonely 26.2 mile journey around a virtual course - but has been assigned a "shadow runner" on earth to bring him closer to the action.
Major Peake will wear a harness tethered to a treadmill to combat weightlessness as he completes the Digital Virgin Money London Marathon challenge in support of The Prince's Trust, of which he is an ambassador.
He will begin his challenge at 10am on April 24 as more than 37,000 runners set off in Greenwich, and will watch a video of the course as he travels on the treadmill.
The charity has selected celebrity fitness coach Tyrone Brennand, 29, from London, to act as Major Peake's legs on earth during the race.
Mr Brennand, who became a young ambassador for The Prince's Trust after setting up his fitness business with the help of the charity, said he was "very proud" and "excited" to act as Major Peake's "shadow runner".
He will complete the course alongside "#TeamAstronaut", which includes European Space Agency runners, who are fundraising for The Prince's Trust.
The astronaut is due to call Mr Brennand from space ahead of the race to wish him good luck.
Major Peake said: "I was very fortunate when I was young to have many opportunities; I was able to fulfil my ambitions. I am acutely aware that many other people do not have these opportunities.
"What The Prince's Trust does in helping disadvantaged young people to make the most of their lives and to fulfil their ambitions is something that I really feel strongly about."