If all goes well, Felix Baumgartner will take about half an hour to get back to Earth during this afternoon's 120,000-foot skydive attempt.
But the veteran Austrian skydiver's preparations for the record-setting jump have taken years. As the key player in the mission, known as Red Bull Stratos, Baumgartner has been planning the jump since 2005. He began taking test dives in a high-pressure suit from as high as 27,000 feet in 2009.
Why so much planning for one jump?
A lot could go wrong. "His blood could boil. His lungs could overinflate. The vessels in his brain could burst. His eyes could hemorrhage. And, yes, he could break his neck while jumping from a mind-boggling altitude of 23 miles," the Associated Press reported.
And that's in addition to the technical difficulties of creating a suit and parachute system for a body that will likely break the sound barrier.
The suit, modeled after those worn by pilots of high-altitude reconnaissance aircraft, will regulate the temperature and pressure Baumgartner experiences and provide him with 100% oxygen throughout the jump.
The parachute system will include a special drogue chute that could help stabilize 'Fearless Felix' if he were to start spinning uncontrollably in the upper atmosphere.
A head-over-feet spin can be life-threatening, as it forces blood into the jumper's extremities—at high pressures, this could cause unconsciousness, and even moderate pressures could damage the brain and eyes, according to National Geographic.
The drogue chute can be manually operated, but it will automatically engage if Baumgartner experiences 3.5 Gs or more continuously for at least six seconds.
It's all a far cry from the 43-year-old Baumgartner's earlier exploits as a BASE jumper, when all he needed to leap off Rio de Janeiro's Christ the Redeemer statue was a parachute.
Follow Baumgartner's jump with HuffPost Science on the liveblog below. For more, check out our in-depth coverage here.
10/14/2012 3:02 PM EDT
GIF: Felix Baumgartner's triumphant reaction after landing safely. twitpic.com/b471d4— BuzzFeed Sports (@BuzzFeedSports) October 14, 2012
10/14/2012 2:18 PM EDT
On The Ground!
10/14/2012 2:16 PM EDT
10/14/2012 2:13 PM EDT
"I Couldn't Have Done It Any Better Myself"
Joe Kittinger on Felix's graceful chute opening.
10/14/2012 2:13 PM EDT
Chute deploys, mission control cheers.
10/14/2012 2:12 PM EDT
Visor Fogging Up
Felix reports that the visor is fogging up, but commentator notes that he's getting to warmer altitude.
10/14/2012 2:10 PM EDT
Felix has reached a stable descent, after spinning briefly and reaching a top speed of 729 mph.
10/14/2012 2:09 PM EDT
10/14/2012 2:06 PM EDT
Door Is Open!
10/14/2012 1:58 PM EDT
Email From Red Bull Stratos
"Felix is now testing his reserve system on the Chest Pack. After this he will decide whether ready to go or not. Felix is now running through the Egress procedure."