UK astronaut Tim Peake is due to set off for the International Space Station (ISS) at 11am GMT from NASA's Kennedy Centre's Cape Canaveral launch pad.
The European Space Agency astronaut joins Tim Kopra of NASA and Yuri Malenchenko of the Russian Federal Space Agency aboard the Soyuz rocket.
He becomes the first state-funded official UK astronaut - with previous Brits either privately funded or adopting a different nationality.
He has already been active on social media, and posted his final Tweet before launch.
This will begin Expedition 46's six month rotation in the space station that famously broke YouTube records when it was featured in a music video of David Bowie's Space Oddity, by NASA astronaut and Commander of the station at the time, Chris Hadfield in 2013.
You can watch the launch live via the Nasa TV website from 10:45am GMT.
Images courtesy of NASA.