Austrian BASE jumper and all-round nutter Felix Baumgartner will be replacing the heights of skyscrapers with somewhere so high you need oxygen to breathe and a suit and helmet that can keep you warm in temperatures of -68 degrees Celsius.
Just after lunchtime today, Baumgartner will begin climbing to an altitude of 36.5km, which is about 120,000ft, in a specially made helium balloon and capsule. Baumgartner will then probably say something memorable before jumping towards earth.
Besides hoping to beat US Air Force Colonel Joe Kittinger's world record skydiving height of 102,800 feet set more than 50 years ago, Baumgartner hopes to break the speed barrier, a feat that has never been officially achieved without aid. Nobody's really quite sure what will happen to his body as he accelerates to more than 690mph and then back down to a subsonic speed as his parachute is deployed.
The stunt will be aired with a 20-second time delay in case something goes wrong – but a measly 20 seconds is nothing when you think how astonishing it will be to see a man jump out a balloon above the earth. And we imagine the two-and-a-half hour ascent before the ten-minute drop will be pretty special, too.
Check out the hopefully record-breaking stunt below. Oh, and have a gander at our Felix Baumgartner Supersonic skydive: Everything you need to know while you wait for it to begin. Don't say we never spoil you.
UPDATE 1: At the moment the mission has been put on hold until 14:30pm GMT at the earliest. While it's nice and calm on the ground, wind speed at 700ft (roughly the height at the top of the balloon) is hitting the high teens, which, according to a spokesman, could cause the capsule to bounce along the ground.
UPDATE 2: According to the video, we'll be seeing more news very soon. We've caught glimpses of the balloon being fettled with so hopefully it will be all systems go very soon.
UPDATE 3: It all begins at 5pm GMT.
UPDATE 4: Following Tuesday's aborted mission, Baumgartner is expected to attempt his skydive at around 1pm today!
UPDATE 5: And he's landed! Felix Baumgartner's supersonic skydive concludes with his safe return to Earth.