* No new launch attempt before Thursday
* Stunt would break altitude record and sound barrier
(Adds background, new details)
By Irene Klotz
Oct 9 (Reuters) - An Austrian daredevil called off his death-defying skydive from a balloon 23 miles (37 km) over the New Mexico desert on Tuesday because of winds at the launch site.
Felix Baumgartner, a 43-year-old helicopter pilot, hot-air balloonist and professional skydiver, had been preparing to break a longstanding altitude record.
But his team announced the launch had been aborted moments after Baumgartner's balloon was set to carry him aloft over Roswell, New Mexico.
"Mission aborted due to gusty winds," a statement on the website of sponsor Red Bull said.
Team spokeswoman Sarah Anderson later said no new launch attempt would be made before Thursday. She said Wednesday had been ruled out due to weather concerns and to give Baumgartner's support crew a day off.
Winds were about 17 mph (27 kph) when the balloon launch was called off at 1:43 p.m. EDT (1743 GMT).
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).
If successful, Baumgartner would be the first parachutist to break the sound barrier but not the first person to fall faster than the speed of sound. On Jan. 25, 1966, Bill Weaver, a test pilot aboard an SR-71 Blackbird aircraft, was ejected over the United States from his damaged plane at Mach 3.18 - more than three times faster than the speed of sound - and survived.
Before Tuesday's launch was scrapped it had already been delayed by nearly five hours because of winds above the launch site.
After the winds subsided Baumgartner, wearing a pressurized spacesuit, climbed into the specially made capsule designed to carry him into the stratosphere. But the gusts then picked up again.
If the launch had proceeded, it would have taken about 2.5 to 3 hours for the 55-story tall balloon to reach 120,000 feet.
Baumgartner's goal is 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.
As he falls from 120,000 feet (36,576 meters) Baumgartner would also break the sound barrier. With virtually no air to resist his fall, he was expected to reach the speed of sound, which is 690 mph (1,110 kph) at that altitude, after about 35 seconds of freefall.
He would 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 his custom spacesuit that will protect him from 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 would be standing by during Baumgartner's skydive.
(Additional reporting by Jane Sutton in Miami; Editing by Tom Brown and Doina Chiacu)
Keywords: USA SPACE/SKYDIVE