If the launch proceeds on Wednesday 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 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.