ROSWELL, N.M. (AP) - Extreme athlete Felix Baumgartner has started his ascent to 23 miles above Earth, hoping to make a death-defying free fall that could make him the first skydiver to break the sound barrier.

Baumgartner took off Sunday in a pressurized capsule carried by a 55-story ultra-thin helium balloon that is expected to take nearly three hours to climb into the stratosphere.

Baumgartner will jump into a near vacuum with no oxygen to begin what is expected to be the fastest, farthest free fall from the highest-ever manned balloon.

Any contact with the capsule on his exit could tear the pressurized suit, a rip that could expose him to a lack of oxygen and temperatures as low as minus 70 degrees. That could cause potentially lethal bubbles to form in his bodily fluids

If all goes well, NASA could certify a new generation of spacesuits for protecting astronauts and provide an escape option from spacecraft at 120,000 feet.