Right now, British astronaut Tim Peake is donning a space suit, preparing to step outside the relative (we've seen Gravity) safety of the International Space Station and go for a spacewalk.
From the when to the why, here are five things you need to know about the historic moment - which you can watch live below.
(Images: NASA, ESA)
When is it happening?
Should everything go according to plan, Major Tim Peake and fellow astronaut Tim Kopra will take part in the 35th NASA Extra-Vehicular Activity (EVA) at 12:55 GMT.
Two hours before they head outside, they'll start "prebreathing" a special mix of air with pure oxygen in their EMU space-suits, to ensure they don't get the bends when working outside.
The walk will last around six hours.
What will they be doing?
Both Tims will be looking to replace the failed Sequential Shunt Unit 1B (a grey box-like device that helps collect power for the station), lay some cables and install a new valve.
The operation will see Tim Kopra head out to remove the failed unit, while Tim Peake will bring the new power box.
Once the installation of the new unit is completed - restoring the station to 100 per cent operational capacity - the pair will look to install new cabling and a valve that will help future remodelling of the space station.
What could go wrong?
Not a lot. But in space, even a small mistake can have huge consequences.
Both astronauts will be tethered to the space station, meaning they can't go drifting off into the void like Sandra Bullock. Both of them will be wearing 'Simplified Aid for EVA Rescue' suits - giant backpacks with small rocket thrusters that will give them the ability to "fly" back to the station should they become untethered.
"The worst possible example is if one of the crew members is completely incapacitated and so he has to be bought back inside", said ESA astronaut Luca Parmitano - who has previously conducted space walks.
Both astronauts have trained for this eventuality in swimming pools back on Earth. Fingers crossed they don't have to call on this training today.
How many Brits have completed a space walk?
Tim Peake will only be the third Brit to walk about in space: Piers Sellers completed six space walks, totalling 41 EVA hours floating about between 2006 and 2011.
Michael Foale - pictured - was born in the UK but took joint American citizenship. In 1999 he became the first Brit to complete a space walk, spending eight hours to replace components of the Hubble Space Telescope.
How can I follow the spacewalk?
The best way to keep up to speed with the spacewalk is to follow events with the @esaoperations Twitter account - who will be live tweeting the events.
A live stream will begin on the European Space Agency Website at 12:00 GMT, which you can find here.