Medic Kevin Fong explains how space harms your body
On 15 December, Tim Peake will launch into space to become Britain's first astronaut on board the International Space Station.
He’ll be carrying out lots of experiments, many of them on his own body – it’s essential to monitor the impact of space travel before attempting longer journeys, perhaps to Mars.
Some of the issues are well known and others are only recently becoming apparent, as medic and space health expert Kevin Fong explains.
Video produced by Sara Barman.