Extreme athlete Felix Baumgartner cancelled his planned death-defying 37-kilometre free fall Tuesday because of high winds, the second time this week he was forced to postpone his quest to be the first supersonic skydiver.

The former military parachutist from Austria had planned to ride a pressurized capsule carried aloft by a 55-story, ultra-thin helium balloon into the stratosphere, and then jump in a specially designed suit.

But winds and delays from a lost radio and problems with the capsule contributed to the decision shortly after 11:30 a.m. MT to abort the mission. Because the balloon is so delicate, it could only take flight if winds were 2 mph or below on the ground.

Baumgartner's team said he has a second balloon and intends to try again, possibly on Thursday.

Plagued by wind, delays

The balloon had been scheduled to launch about 6:30 a.m. from a field near the airport in a flat dusty town that is best known for a rumoured 1947 UFO landing. But high winds kept the mission in question for hours.

When winds died down, Baumgartner, 43, suited up and entered the capsule and crews began filling the balloon. But the team's discovery it had lost one of two radios in the capsule and a problem with the capsule led to delays in the decision to begin filling the balloon, pushing the mission critically close to a noon cutoff for launch.

As the balloon was finally filling, a gust of 25 mph whipped it around and could have damaged its integrity, mission technical director Art Thompson said. "Not knowing if the winds would continue or not, we made the decision to pull the plug," he said.

Mission meteorologist Don Day said, "it was just a situation where it took too long" and they lost their already pushed-back launch window.

Day was shown on a live video feed shaking his head as he watched the latest weather data just before the mission was halted. "I was very despondent because I could see the end right there," he said.

Pilot Felix Baumgartner shows a piece of the balloon material he'll be using for his ascent. (Joerg Mitter/Red Bull Stratos/AP)

After sitting fully suited up in his capsule for nearly 45 minutes, Baumgartner was shown on a live video feed leaving the capsule and departing the launch site in his Airstream trailer.

Thompson said the earliest the team could try again would be Thursday because of weather and the need for the crew — which worked all night Monday into Tuesday — to get some rest.

Baumgartner was to make a nearly three-hour ascent to about 36,500 metres, then take a bunny-style hop from a pressurized capsule into a near-vacuum where there is barely any oxygen to begin what is expected to be the fastest, farthest free fall from the highest-ever manned balloon.

Risky jump

Baumgartner spent Monday at his hotel, mentally preparing for the dangerous feat with his parents, girlfriend and four close friends, his team said. He had a light dinner of salmon and a salad, then had a massage. He spent Tuesday morning resting in an Airstream trailer near the launch site.

The mission carried several risks: any contact with the capsule on his exit could tear the pressurized suit. A rip could expose him to a lack of oxygen and temperatures as low as –57 C. It could cause potentially lethal bubbles to form in his bodily fluids, a condition known as "boiling blood."

Felix Baumgartner falls during a 7,600-metre high test jump in 2010. (Luke Aikins/Red Bull Stratos/AP)

He could also spin out of control, causing other risky problems.

The energy drink maker Red Bull, which was sponsoring the feat, had been promoting a live internet stream of the event at http://www.redbullstratos.com/live from nearly 30 cameras on the capsule, the ground and a helicopter. Organizers said there would be a 20-second delay in their broadcast of footage in case of a tragic accident.

Despite the dangers and questionable wind forecast, high performance director Andy Walshe had said earlier that the team was excited, not nervous. Baumgartner had made two practice jumps, one from 24 kilometres in March and another from 29 kilometres in July.

"With these big moments, you get a kind of sense that the energy changes," he said Monday. "It really is just kind of a heightened energy. It keeps you on your toes. It's not nervousness, it's excitement."

Valuable scientific data

During the ascent, Walshe said, the team would have had views from a number of cameras, including one focused directly on Baumgartner's face. Additionally, they would have had data from life support and other systems that show things like whether he is getting enough oxygen.

The team was also expecting constant communication with Baumgartner, although former astronaut Joe Kittinger, whose 1960 free-fall record from 31.4 kilometres Baumgartner hopes to break, is the only member of mission control who will be allowed to talk to him.

And while Baumgartner had hoped to set four new world records, his free fall was more than just a stunt.

His dive from the stratosphere would have provided scientists with valuable information for next-generation spacesuits and techniques that could help astronauts survive accidents.

Jumping from more than three times the height of the average cruising altitude for jetliners, Baumgartner's was expected to hit a speed of 1110 km/h or more before he activated his parachute at 2.9 kilometres above sea level, or about 1.5 kilometres above the ground in southeastern New Mexico. The total jump would have taken about 10 minutes.

His medical director is Dr. Jonathan Clark, a NASA space shuttle crew surgeon who lost his wife, Laurel Clark, in the 2003 Columbia accident. No one knows what happens to a body when it breaks the sound barrier, Clark said.

"That is really the scientific essence of this mission," Clark, who is dedicated to improving astronauts' chances of survival in a high-altitude disaster, said earlier Tuesday.

Clark told reporters Monday he expected Baumgartner's pressurized spacesuit to protect him from the shock waves of breaking the sound barrier. If Baumgartner survived the jump, NASA could have certified a new generation of spacesuits for protecting astronauts and provide an escape option from spacecraft at 36.5 km, Clark had said.

Currently, spacesuits are certified to protect astronauts to 30.5 kilometres, the level Kittinger reached in 1960. Kittinger's speed of 988 km/h was just shy of breaking the sound barrier at that altitude.

With files from CBC