UPDATE: They've decided to call the jump off because of gusty winds. The winds caused a five hour delay this morning from the original starting time. The winds died down eventually and they thought they had a window, but problems with the capsule's communications systems delayed getting everything set. They had the balloon almost filled when the winds picked back up and it became clear it was too dangerous to take off. 

Sad astronauts:

They might try again tomorrow, but there's no guarantee the winds will be calm enough. The forecast says the wind will be higher than today, according to Weather Underground. Thursday seems like the most likely day the jump could occur. 

Original: Daredevil parachutist Felix Baumgartner will attempt to break the record for the highest sky dive ever today and his death-defying free fall will be broadcast live on YouTube. If successful, Baumgartner will step out of a custom-made, 55-story hot air balloon more than 120,000 feet above the Earth, fall more than 100,000 feet (about 22 miles) in five-and-a-half minutes, reach a top speed of 690 miles-per-hour, and become the first human to break the sound barrier without the help of a jet airplane.

The mission (sponsored by Red Bull, which has become the go-to bankroller of the world's craziest ideas) has taken five years of training a lot of helpful advice from Joe Kittinger, the retired Air Force colonel who set the top altitude and speed records as a space program pioneer in 1960.

The launch of the balloon was delayed for several hours due to wind conditions, but his team is still aiming for a launch today—current start time is scheduled around 1:00 p.m. ET—and is preparing for liftoff. It will take two-to-three hours to reach the jump height once he begins the ascent. As Baumgartner explained to The New York Times, being crammed into a tiny capsule for such a long time is actually the hardest part of the ordeal, as the mind has a tendency to freak out in such situations.

You can keep track of of Baumgartner's progress on the Red Bull Stratos website, or their Twitter feed, and also watch stream below.