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.
CLICK HERE OR SCROLL DOWN FOR LIVE UPDATES
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.
GIF: Felix Baumgartner's triumphant reaction after landing safely. twitpic.com/b471d4
— BuzzFeed Sports (@BuzzFeedSports) October 14, 2012
Joe Kittinger on Felix's graceful chute opening.
Felix reports that the visor is fogging up, but commentator notes that he's getting to warmer altitude.
Felix has reached a stable descent, after spinning briefly and reaching a top speed of 729 mph.
"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."
From Misson Control, Joe Kittinger runs through checklist in run-up to Baumgartner's leap.
As per Baumgartner's request, flight mentor Joe Kittinger is the only one speaking to him through mission control.
In 1961, Joe Kittinger made a record-setting jump from 102,800 feet. A little background on Kittinger here (VIDEO).
"The decision has been made. Felix Baumgartner will jump," the Red Bull Stratos live feed commentator announced.
Baumgartner and Mission Control are beginning a second checklist run-through.
"Felix raised an issue with the heat in his visor faceplate. The team currently sees no fog on the faceplate; however Mission Control is investigating the issue. Joe Kittinger from Mission Control enabled a private conversation between himself and Felix. We will keep you updated with updates on the issue as soon as we have them."
Mission Control says Baumgartner will jump. Other possibility would have been for him to have descended inside capsule.
According to YouTube stats, more than 5.2 million people are watching Felix Baumgartner's live jump on Red Bull Stratos's video stream.
Bear in mind that these shots of the balloon are coming from mission control. 115,000 feet and still crystal clear.
Mission Control reportedly troubleshooting problem with heating element in Baumgartner's facemask.
Mission control concerned that the balloon is ascending too slowly. It may be necessary to drop more ballast.
Felix Baumgartner now higher than the maximum altitude of U2 spy plane: 70,000+ ft #livejump
— James Offer (@joffley) October 14, 2012
#livejump anyone notice they aren't playing the voice communications anymore? #problem no visor heat!
— DB (@bondoa6) October 14, 2012
*Drink an ice-cold beer
Mission control says we can expect the teardrop-shaped capsule to fatten up as the helium inside expands. The balloon material is 0.001 inch thick--"ten times thinner than a sandwich bag," according to mission control.
Loading comments… 
Posted: 10/14/2012 12:36 pm EDT Updated: 11/13/2012 1:08 pm EST