On Wednesday, Baumgartner took another stratospheric leap, this time from an altitude of more than 29km — nearly three times higher than cruising jetliners. He landed safely near Roswell, New Mexico.

His top speed was an estimated 862.5kph, said Brian Utley, an official observer on site.

Supersonic

It's the second test jump for the Austrian-born Baumgartner from such extreme heights and a personal best. He's aiming for a record-breaking jump from 38,100 metres, or 37 kilometres, in another month. He hopes to go supersonic then, breaking the speed of sound with just his body.

"It has always been a dream of mine," Baumgartner said in a statement following Wednesday's feat. "Only one more step to go".

Longtime record-holder Joe Kittinger jumped from 31.38km in 1960 for the Air Force. Kittinger monitored Wednesday's dry run from a mini Mission Control in Roswell.

As he did in March, the 43-year-old ascended alone in an enclosed capsule lifted by a giant helium balloon that took off from Roswell. He wore a full-pressure suit equipped with parachutes and an oxygen supply — there's virtually no atmosphere that far up.

It took about 1 hours to reach his target altitude. He was in free fall for an estimated three minutes and 48 seconds before opening his parachutes.

No control

"It felt completely different at 90,000 feet," Baumgartner noted. "There is no control when you exit the capsule. There is no way to get stable."

In March, Baumgartner jumped from 21,818 metres, more than 20.9km, saluting before stepping from the capsule. Bad weather earlier this week delayed the second test jump until Wednesday.

NASA is paying close attention to this Red Bull-funded project dubbed Stratos, short for stratosphere. The space agency wants to learn all it can about potential escape systems for future rocketships.

Space

Baumgartner won't come close to space, even on the ultimate jump that's planned for late August or early September. Space officially begins at 100km.

Baumgartner, a former military parachutist and extreme athlete, has jumped more than 2,500 times from planes and helicopters, as well as from skyscrapers and landmarks, including the 101-story Taipei 101 in Taiwan.

Kittinger, who turns 84 on Friday, was an Air Force captain when he made his historic jump for what was called Project Excelsior. He reached 988kph on that dive, equivalent to Mach 0.9, just shy of the sound barrier.

Baumgartner expects to accelerate to 1,110kph on his final plunge.