Felix Baumgartner is making the jump in a space suit, helmet and parachute. He's being ballooned 23 miles up, where he'll begin the jump.
Baumgartner, who is being sponsored by Red Bull, could be the first human being to break the sound barrier without the assistance of a mechanical device like an airplane or spacecraft. Because the air is so thin at that altitude, 40 seconds into the jump he should hit 690 miles an hour.
To give you some perspective, he'll jump from a height more than 3 times the cruising altitude of a commercial jet.
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