This crazy Austrailian,  Felix Baumgartner, is going to attempt a base jump from 23 (miles) above the Earth surface.  He's wearing a space suit of sorts for oxygen and warmth but the real risk is in the speed he's going to reach. 

690 mph!!!  That's faster than sound!  The fear is that his body could go into an uncontrollable spin which could potenitally lead to a gruesome outcome.

His blood could boil. His lungs could overinflate. The vessels in his brain could burst. His eyes could hemorrhage. Yikes!!

Here's a cool preview of what he hopes for.