Skydiver to attempt record-breaking jump from stratosphere

* Austrian daredevil tries to break the sound barrier

* Specially designed spacesuit needed to protect him

* Current record was set in 1960 by a U.S. Air Force colonel

By Irene Klotz

Oct 8 (Reuters) - An Austrian adventurer is preparing toskydive from a balloon flying 23 miles (37 km) above New Mexicoon Tuesday, seeking to break a long-standing altitude record -and the soundbarrier - in the process.

Felix Baumgartner, a 43-year-old helicopter pilot, hot-airballoonist and professional skydiver, would become the firstperson to freefall from that high up in the stratosphere, aregion more like the vacuum of space than the oxygen-richatmosphere closer to Earth.

Weather will be key. Baumgartner's team decided to wait outa cold front moving through the area on Monday before launchingthe massive but fragile helium balloon that will carry him to analtitude of 120,000 feet (36,576 meters) above Roswell, NewMexico.

If the weather is good, the balloon will be launched at dawnon Tuesday, around 7 a.m. New Mexico time (9 a.m. EDT/1300 GMT).It takes about 2.5 to 3 hours to reach 120,000 feet.

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

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

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

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

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

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

The near-vacuum puts him at risk of ebullism, a potentiallylethal condition in which fluids in the body turn to gas and theblood literally boils. Severe lung damage could occur withinminutes.

Helicopters equipped with newly developed instruments totreat lung damage will be standing by during Baumgartner'sskydive.

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

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

Clark's wife, shuttle Columbia astronaut Laurel Clark, diedalong with six crewmates when the spaceship broke apart overTexas on Feb. 1, 2003, as it headed for a landing in Florida.

Baumgartner's jump is sponsored by Red Bull, which will bewebcasting the event live at redbullstratos.com

(Editing by Jane Sutton and David Brunnstrom)

((1 305 810-2688)(miami.newsroom@thomsonreuters.com))