An Austrian adventurer is preparing to skydive from a balloon flying 23 miles (37 km) above New Mexico on Tuesday, seeking to break a long-standing altitude record - and the sound barrier - in the process.
Felix Baumgartner, a 43-year-old helicopter pilot, hot-air balloonist and professional skydiver, would become the first person to freefall from that high up in the stratosphere, a region more like the vacuum of space than the oxygen-rich atmosphere closer to Earth.
Weather will be key. Baumgartner's team decided to wait out a cold front moving through the area on Monday before launching the massive but fragile helium balloon that will carry him to an altitude of 120,000 feet (36,576 meters) above Roswell, New Mexico.
If the weather is good, the balloon will be launched at dawn on 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) 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 Jane Sutton and David Brunnstrom)