Felix Baumgartner, a 43-year-old helicopter pilot, hot-air balloonist and professional skydiver, would break a longstanding altitude record and the sound barrier if the jump goes forward.

Weather will be key. Baumgartner's team issued a statement saying the launch of the massive but fragile helium balloon that would carry him to an altitude of 120,000 feet (36,576 meters) above Roswell, New Mexico, had been rescheduled for 1:30 p.m. EDT (1730 GMT).

The launch, originally scheduled for around 9 a.m. EDT (1300 GMT), was delayed by winds between about 700 feet (213 meters) and 800 feet (244 meters) above the launch site, the team said.

"We're on hold, waiting," Sarah Anderson, a spokeswoman for the team, told Reuters in an e-mail.

If the launch proceeds it would take about 2.5 to 3 hours to reach 120,000 feet.

The 30-million-cubic-foot (850,000-cubic-meter) plastic balloon, which is about one-tenth the thickness of a Ziploc bag, cannot handle winds greater than 6 miles per hour (9.7 km per hour). The balloon will carry a specially made space capsule where Baumgartner will spend the ride into the stratosphere.

Baumgartner hopes to break the record of 102,800 feet (31,333 meters) for the highest-altitude freefall, a milestone set in 1960 by U.S. Air Force Colonel Joe Kittinger.

By jumping from 120,000 feet (36,576 meters) Baumgartner will also break the sound barrier. With virtually no air to cushion his fall, he is expected to reach the speed of sound, which is 690 mph (1,110 kph) at that altitude, after about 35 seconds of freefall.

He will stay supersonic for nearly a minute and should freefall for a total of 5 minutes and 35 seconds.

When Baumgartner jumps from the capsule, the position of his body will be crucial, since there is no air for him to move around in. If he falls in a way that puts him into a rapid spin, Baumgartner could pass out and risk damaging his eyes, brain and cardiovascular system.

Baumgartner's safety gear includes a custom spacesuit to protect him from the low pressure and the extreme cold. Temperatures are expected to be as low as about minus-70 degrees Fahrenheit (minus-57 degrees Celsius.)

The near-vacuum puts him at risk of embolism, a potentially lethal condition in which fluids in the body turn to gas and the blood literally boils. Severe lung damage could occur within minutes.

Helicopters equipped with newly developed instruments to treat lung damage will be standing by during Baumgartner's skydive.

"What we're doing here is not just a record attempt. It's a flight test program," project adviser Jonathan Clark, a medical doctor and former NASA flight surgeon, told reporters during a news conference on Monday.

Among those interested in the spacesuit research are commercial companies developing spaceships for passenger travel. The research could help people survive a high-altitude accident.

Clark's wife, shuttle Columbia astronaut Laurel Clark, died along with six crewmates when the spaceship broke apart over Texas on February 1, 2003, as it headed for a landing in Florida. (Editing by Tom Brown and Doina Chiacu)

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