* Stunt would break altitude record and the sound barrier
* Not clear how long launch window will remain open
* Fragile balloon cannot handle strong winds
(Adds background) By Irene Klotz
Oct 9 (Reuters) - Plans for an Austrian daredevil to skydive from a balloon 23 miles (37 km) over the New Mexico desert were on hold on Tuesday due to winds, but his team said the death-defying stunt could still happen later in the day.
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 early Tuesday morning 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 delayed until at least 9:30 a.m. EDT (1330 GMT).
The delay was prompted by winds at about 700 feet (213 meters) above the launch site, the team said.
It was not immediately clear how long the window for the possible launch would remain open but it takes 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 current 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 ebullism, 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 Feb. 1, 2003, as it headed for a landing in Florida.
Baumgartner's jump is sponsored by Red Bull, which will be webcasting the event live at redbullstratos.com
(Editing by Tom Brown and Doina Chiacu)
Keywords: USA SPACE/SKYDIVE