If the wind blowing across the New Mexico desert drops, a 43-year-old Austrian man will step out of a small silver capsule on Tuesday and attempt to make history.
Felix Baumgartner is to jump from the largest helium-filled balloon ever built for manned flight and hurtle towards the Earth from near the edge of space, 23 miles up.
He will reach a speed of 690mph, becoming the first man to break the sound barrier in freefall, before deploying his parachute.
If it goes wrong, the project's medical director, Jonathan Clark, says cheerfully, Baumgartner's skin will boil. Baumgartner explained in a recent interview that he "loves a challenge".
He made his first parachute jump at 16, the earliest Austria would permit it, and joined the army to continue his training. He hates being called an adrenaline junkie, saying: "I like the planning."
Both Baumgartner and Red Bull Stratos, which has spent five years and undisclosed millions preparing the stunt, say the purpose is "to advance scientific discoveries in aerospace for the benefit of mankind". It is also, as one commentator has said, one giant leap for publicity.
With five days to go, the attempt was put back by 24 hours due to forecasts of strong winds.
A weekend dress rehearsal went well and the forecast looks good for Tuesday. There have been two test jumps, including one in July from just over 90,000 feet up.