Felix Baumgartner is aiming to jump from a higher altitude than anyone ever has -- 120,000 feet (about 23 miles), more than three times the cruising altitude of the average airliner -- with nothing but a space suit, helmet and parachute.

He also hopes to be the first person to break the sound barrier. At that altitude, the thin air provides so little resistance that after just 40 seconds, he is expected to be free-falling faster than 690 miles an hour.

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