British astronaut Tim Peake is currently heading skyward aboard a Russian Soyuz rocket, heading beyond the Earth's atmosphere to the International Space Station (ISS).
Just after 11am today, Peake took off from the Baikonur Cosmodrome launch pad in Kazakhstan. You can watch his mission live here:
Once he reaches his destination, he'll spend the next six months carrying out a series of experiments – some of which will be on himself – to further our understanding of science.
There has been a lot of hype about Peake's mission, not least because it's the first time the European Space Agency (ESA) has sent a British astronaut into space. In fact, he's currently the UK's one and only official astronaut.
So, who exactly is Tim Peake, and what will he be doing over the course of the mission? Here's everything you need to know.
Tim Peake: From military man to pilot
Peake spent 20 years in the military, travelling to places like Afghanistan, Bosnia and Northern Ireland.
The 43-year-old's next step was to become a commercial pilot, and it was only after being accepted onto the ESA's training programme in 2009 that he moved into space travel.
The first British person to be taken on by the ESA
Peake beat 8,000 other people in the application process, and his success makes him the first ever British astronaut to be employed by the ESA.
He wasn't the first British person to go to space, however - this was Helen Sharman, who went into orbit in 1991.
It has been a tough six years for the former military man – between being selected and today's mission, he has had to complete 6,000 hours of medical, physical and academic training.
He left from Kazakhstan
Kazakhstan is home to the Baikonur Cosmodrome, the world's first and largest operational space launch facility. Located deep in the county's desert steppe – a vast region of grasslands – it is absolutely huge, measuring 90km by 85km.
Vostok 2, the world's first manned spacecraft, and Sputnik 1, the first orbital spaceflight, were both launched from this pad.
Science, science, science
The purpose of this mission is to carry out a series of complex science experiments. Among other things, Peake will grow proteins for drug research and use an electomagnetic levitating device to study new metals.
Peake will also treat himself like a guinea pig, studying how his bone density and blood pressure are affected by being in space. This will shed light on how humans could survive in space in the future.
An intergalactic Christmas
Peake will spend Christmas Day at the ISS. He won't be totally deprived of earthly pleasures, though - a Christmas pudding and bacon sandwich made by chef Heston Blumenthal are being delivered to the ISS for his enjoyment.
During a Q&A session at the Science Museum in London last month, Peake said he was taking a pack of balloons, some Christmas presents and family photographs up with him.
But he won't be alone
Peake is being joined on the mission by Tim Kopra, a US astronaut, and Russian commander Yuri Malenchenko.
Together, the trio will travel round the earth at a speed of 17,500 mph. By the end of the mission, they will have completed 2,700 laps.