For a supersonic skydive, first comes practice (photos)

In 1947, Air Force Capt. Chuck Yeager became the first person to fly an aircraft faster than the speed of sound. Sometime later this year, Austria's Felix Baumgartner wants to become the first human to achieve these speeds without the luxury of doing so in aircraft: He plans to do it in an open freefall.

Riding a capsule carried by a balloon to the edges of space, more than 23 miles up, Baumgartner plans to step out of the capsule at about 120,000 feet, then hurtle toward the Earth at more than 768 miles per hour -- faster than the speed of sound.

In this photo, Baumgartner stands at the edge of the capsule ready to jump from an altitude of 71,581 feet during preparations for the Red Bull Stratos project above New Mexico. He's made more than 2,000 jumps in his lifetime, but this jump, on March 15, 2012, was his highest jump yet. At 71,581 he is above the mark known as the "Armstrong Line," the point of altitude at which the atmospheric pressure is so low (0.0618 atmosphere) that bodily fluids would, essentially, boil at human body temperature, requiring a protective, pressurized spacesuit.

The launch balloon ascends to more than 71,000 feet during the first manned test flight for Red Bull Stratos in Roswell, N.M., on March 15. The eventual supersonic jump, which will occur at an unspecified future date, will be from an incredible 121,000 feet. If he accomplishes that rarefied feat, he will have surpassed the achievement of the legendary Joe Kittinger, an Air Force officer who in 1960 parachuted from unpressurized balloon gondola at an altitude of 102,800 feet and who came just short of reaching supersonic speeds -- his descent topped out at about 614 miles per hour

In 2010, Baumgartner's original planned jump was put on hold due to legal complications, but he's back and ready to try the jaw-dropping jump again.

Here, Baumgartner prepares for a wind tunnel test in Perris, Calif., in February 2010. The pressurized spacesuit Baumgartner must wear to protect himself from the blood-boiling altitudes severely restricts his motions.

Famous for his daredevil BASE jumps and freefalls, on December 11, 2008, Baumgartner leaped off the world’s tallest building, the 1,666-foot "Taipei 101 Tower" in Taiwan.

The Brooks Altitude Chamber at Brooks Air Force Base in San Antonio, Texas, was used to simulate altitudes of 121,000 feet, where temperatures reach -50 degrees Fahrenheit.

This is the interior of the capsule at the Brooks testing chamber.

The Red Bull Stratos camera systems maintain constant visual contact with Baumgartner during testing in the pressurized Brooks capsule, as here on November 8, 2011.

A look at the mission control center during the first manned test flight for the Red Bull Stratos in Roswell, N.M. on March 15, 2012.

A crew member inspects the capsule following recovery of the launch capsule during tests for the Red Bull Stratos project in Roswel in March.

Felix Baumgartner and life support engineer Mike Todd celebrate after a test flight.

Baumgartner rides a forklift to reach the capsule which is hoisted by a crane. This is minutes before a manned test flight on March 15. In this test he reached 71,581 feet and landed safely near Roswell.

In 2003, Baumgartner flew across the English Channel wearing a carbon wing.