Two daredevil parachutists are competing to become the first person to break the sound barrier unaided in a freefall jump from a balloon.
Michel Fournier, of France, and Rodd Milner, an Australian ex-commando, are both scrambling to gather the funds for separate attempts to leap from balloons at 40,000m (131,200ft or 25 miles), twice the cruising height of Concorde and four times as high as Everest.
So far Mr Fournier, 57, a former army officer, has had to put off at least two attempts after failing to agree take-off and landing points with the authorities in France. He hopes to make his jump between May and September. Mr Milner intends to jump from above Alice Springs in May and has the unofficial backing of the Australian government.
Breaking the sound barrier means travelling faster than 760mph, or 1 mile every five seconds. Highly specialised equipment is required just to survive the trip to the jumping-off point. At 40,000m, the temperature is minus 20C (minus 4F), falling to minus 60C further down, and the air has negligible oxygen content. The extreme conditions call for a spacesuit, which has internal heating and more than three hours' oxygen.
Both men are planning to be towed aloft by a helium-filled balloon. Mr Milner said: "By the time it gets to 131,000ft, the expansion of the helium will make the balloon the size of two jumbo jets."
They intend to travel in caskets that will protect them from intense ultra-violet radiation from the Sun; the Earth's atmosphere gives barely any protection. The parachutists will then jump and freefall, not opening their parachute for six minutes. Mr Milner said the project would have a real application: "This will be utilised for future space travel as emergency procedures as people start leaving the atmosphere."
Researchers calculate a body falling in the stratosphere will reach the speed of sound in 180 seconds. The terminal velocity of a skydiver at that altitude could reach 1,119mph but as they get lower the increasing thickness of the Earth's atmosphere will slow them, while heating the outside of their suit.Reuse content