Felix, top, before he jumped off a balloon from 71,581 feet during a test jump in March this year.Photo: AP
For 23 miles up on the edge of space, and wearing only a pressurised suit and a parachute, Felix Baumgartner will pause at the hatch of his tiny capsule as it ascends into the heavens beneath one of the biggest balloons ever made.
The sponsor Red Bull Stratos announced on Friday that the jump by extreme athlete Baumgartner, 43, have been moved from Monday to Tuesday. The jump can only be made if winds on the ground are under 2mph for the initial launch a balloon carrying Baumgartner.
No more than 20 minutes later, the world will know whether this audacious Austrian has become the first skydiver to break the sound barrier in the highest, fastest freefall descent in history.
If anything goes wrong - and despite five years of planning and training, there is plenty that could - it might get very, very messy.
The nightmare scenario that Felix's project director likens to a 'horror film' would involve his blood boiling, brain bursting and eyeballs popping out - all of it watched live via the internet around the globe.
Felix has clocked up 2,500 skydiving jumps, including one in which he became the first person to 'fly' across the English Channel, with carbon-fibre wings strapped to his back.
Baumgartner says his supersonic plunge will be the end of his 'journey' as a daredevil.
Ahead of his grand finale, he has completed a couple of high-altitude dress rehearsals. In July, he leapt from 96,640ft - just 6,000ft shy of a world record set in 1960 by Joe Kittinger, a US air force test pilot.
A specially designed £125,000 spacesuit has an insulating exterior that can withstand extreme temperatures, and an airtight inner layer filled with pressurised oxygen.
The suit's 12lb chest pack contains monitoring and tracking equipment together with a voice transmitter so he can talk to mission control on the way down. The pack is connected to a device on his wrist that allows him to monitor his speed and altitude.
The capsule in which he'll make his ascent is 11ft high and 8ft in diameter, made from fibreglass strengthened by an internal metal frame, and weighs as much as a Volkswagen Beetle.
The air pressure inside the capsule will still be significantly lower than at sea level, and any kind of gas inside his body could prove extremely uncomfortable.
Weather permitting (the balloon material is so flimsy the ground level wind cannot be stronger than 2mph), the launch is scheduled for dawn on Tuesday, on a runway in the New Mexico desert.
The helium balloon is as high as a 55-storey building with a volume of 30million cubic feet. Made from strengthened plastic, it is a tenth of the thickness of a sandwich bag.
Baumgartner has limited space to move around in the capsule and the balloon will be largely steered remotely from mission control down on the ground.
As a safety precaution of sorts, his clever spacesuit will release a drogue parachute - a miniaturised version of the type used to slow fast-landing jets - to reduce his speed if its monitoring system senses he has lost consciousness.
It will take him just 40 seconds to go from zero to 700mph and break the sound barrier at an altitude of around 100,000ft.
His spacesuit fitted with cameras recording his stomach-churning descent, will freefall for some five-and-a-half minutes before pulling his main parachute at 5,000ft. Some ten to 15 minutes later, with luck he will touch down battered but unbowed near Roswell.
If all goes well, the journey will take just under three hours. The biggest danger he faces on the way up is the risk of the balloon rupturing soon after take-off. If that happens, Fearless Felix won't have time to open the hatch and get out, and will come crashing down inside the capsule.
When it reaches the jumping height of 120,000ft - three times the altitude at which airliners fly - he will look out on a black rather than blue daytime sky while he waits for the final 'clear to jump' message from mission control.