Teetering 23 miles above the New Mexico desert, Felix Baumgartner plans to leap head first into the abyss and become the first free-falling human to break the sound barrier as he plummets to the ground.

The feat will put his life on the line and push his body to the limit as when he falls from 120,000 feet in the air.

Wearing a newly designed pressurized suit and helmet, the Austria native will test the threshold of his equipment as scientists, aerospace engineers, the Air Force and NASA study what it shows about the limits and capabilities of the human body bailing out from aircraft at ultra-high altitudes. After several years of preparation and test jumps, Baumgartner, 43, is ready. "I feel like a tiger in a cage waiting to get out," he said.

The jump -- which could be made as early as Tuesday, depending on a cold front -- is an effort to break a free-fall world record of more than 19 miles, or 102,800 feet, set in 1960 by Air Force test pilot Joe Kittinger, who is serving as an adviser on this mission. The endeavor, called Stratos, is funded by the energy drink company Red Bull.

'This is beyond extreme'

Clearly, Red Bull has things in mind besides scientific breakthroughs. The mission involves two dozen cameras, including a helmet cam, to catch the action and to deliver live Web streams.

This jump is "unprecedented" and risky, said Kelly O'Keefe, a marketing professor at Virginia Commonwealth University. "This is beyond extreme. The risk of failure is so high."

The company and mission organizers reject talk of the event being done solely for publicity.

"This is a flight test program, not a stunt," said Art Thompson, technical project director. "Sure, we're breaking a 52-year-old record, but we're developing technology that will benefit humanity for decades to come."

In addition to testing the new space suit and high-altitude limitations on the human body, Stratos aims to find out whether GPS equipment can function and whether the parachute can provide adequate stabilization.

Baumgartner will be carried skyward inside a pressurized capsule suspended from the largest balloon ever used in a manned flight. Most of the equipment involved was built by Sage Cheshire Inc., a small aerospace firm in Lancaster, Calif., founded by Thompson in 2002.

Supersonic in 35 seconds

The pressurized capsule, weighing 2,900 pounds -- a little more than a Volkswagen beetle -- will be carried by a massive, helium-filled balloon to an altitude of 23 miles near Roswell, N.M. The trip will take up to three hours, and temperatures will fall as low as minus 70 degrees.

Once Baumgartner jumps from the capsule, he's expected to become supersonic within 35 seconds and ultimately reach about 700 mph. After free falling an additional five minutes, he will deploy his parachute. About 15 minutes later, Baumgartner should reach the ground. In all, his descent is expected to last 20 minutes.

Without a pressurized suit, his body fluids would begin to "boil" from lack of atmospheric pressure above 62,000 feet. The suit helps stop nitrogen from forming bubbles in his blood and bringing on decompression sickness. He will also wear an instrument pack to monitor heart and respiratory rates and an 8-pound helmet providing oxygen.

Baumgartner, who lives in Switzerland, is an accomplished jumper who has parachuted from a variety of structures, including the Jesus statue in Rio de Janeiro and one of the world's tallest buildings, Taipei 101 Tower in Taipei, Taiwan.

Describing the dangers, Dr. Jonathan Clark, the mission's medical director and former NASA flight surgeon, said: "On the ascent, it starts with the potential for balloon failure in the first few thousand feet, when there wouldn't be enough time for the capsule parachute to deploy or for Felix to bail out. As he gets higher in the atmosphere, low pressure and oxygen deprivation could render him unconscious in seconds if his life-support systems were breached."

But the team is confident, he said. "We wouldn't launch if we didn't think Felix was ready."