Within the hour, Felix Baumgartner will step out of a capsule at the edge of space. He'll jump out at 120,000 feet in an attempt to break the speed of sound in freefall.
That is Baumgartner will have to travel at more than 700 miles per hour with the help of an engine.
It's a risky attempt that All Things Considered's Audie Cornish spoke to Baumgartner about back in May.
Audie asked him if there were any concerns about a human body travelling at this speed.
"Well, mostly, the scientists, they think you cannot maintain your normal freefall position, so it would start flat-spinning," he said. "And if that occurs and it's faster than 150 RPM, there's only one way for your blood to leave your body, and that's through your eyeballs."
Baumgartner and his team are live streaming the jump. We've embedded live video at the bottom of this post. Baumgatner is supposed to step out the capsule at 1:40 p.m. ET.