Major Tim Peake will make history today as he becomes the first Briton walk in space.
Although Peake has only spent four weeks aboard the International Space Station, this is a task that has taken him months of preparation at NASA’s Johnson Space Center.
Amidst all the excitement and the numerous facts and figures about the historic moment, the most important thing to bear in mind is why it's happening in the first place.
Peake and his colleague from NASA, Tim Kopra, have been tasked with replacing a faulty unit.
Both astronauts will head past the white radiators to the Solar Arrays in the background of this picture.
Once outside, the first thing both Tims will have to do is "buddy-check," to ensure all the equipment is in place and to orient themselves with their new environment, the European Space Agency have stated.
Kopra will be first to head over to what is known as the Sequential Shunt Units (SSU), using his arms to move along the outside of the International Space Station (ISS).
If you're wondering what the SSU is - it is what the ISS' solar panels are connected to and it is essentially a rectangular box.
At this point, time is of the essence as the repairs should be carried out while the ISS is still on the night side of the Earth.
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According to the British Interplanetary Society, this should take no longer than 15 minutes.
In order to ensure the new replacement part is aligned properly ESA have said both astronauts will be counting the turns while securing the bolt.
Ground control will then perform a few checks to ensure everything is working as it should be and both Peake and Kopra will head back to the airlock where they will keep the faulty unity for inspection - and that should take three hours.
The second part of the spacewalk has everything to do with laying cables.
At the airlock, Peake will pick up a bag of cables to lay, to fix one of the ISS labs known Destiny. While he's working away, Kopra will be installing a valve.
So, what happens if both Tims finish ahead of time? Well, ground control will have more tasks set up including more cable-laying.
There is no rest for those who walk in space.