Baumgartner gives supersonic skydive a go (live video) - CNET

Felix Baumgartner will have five cameras on him to record his historic skydive.

(Credit: Red Bull Stratos )

Felix Baumgartner aims to make history today as the first person to achieve supersonic speed in freefall.

As if that weren't enough, he will be starting his descent from higher than anyone else has ever ascended in a manned balloon flight: 120,000 feet, or 23 miles above the Earth.

The daredevil's jump comes after years of preparation and delays, and replete with a full array of high-tech gear, from the 2,900-pound "space capsule" slung under a 550-foot-tall (at launch) helium balloon that will carry him aloft in an approximately 2-hour ascent, to the custom-made full-pressure suit that will protect him from the very real dangers of the thin and frigid air.

Sensors in a chest pack will log all the relevant data for vetting by the Federation Aeronautique Internationale, the body that governs air sports and aviation records. Gear in the pack includes GPS tracking device, inertia measurement unit, HD camera, and voice transmitter and receiver.

Baumgartner's team, Red Bull Stratos, is live-streaming the jump, which is taking place in the vicinity of Roswell, N.M. You can watch it here, starting at about 5:30 a.m. PT / 8:30 a.m. ET:

There's more than mere bragging rights behind the extreme altitude as the starting point. It's also a practical consideration, with two key components: air temperature and air density. In the subzero stratospheric atmosphere, sound travels more slowly, so Baumgartner doesn't have to travel quite as fast to go supersonic -- his backers reckon he'll need to hit 690 mph to achieve Mach 1. And the thin air at that altitude is less dense, so that there's less resistance to a body moving through it.

The 43-year-old Baumgartner also will need to exercise some serious body control to get into the most streamlined position possible for his freefall, which is expected to last roughly 5 minutes, 35 seconds (which also would be a record, outdoing the existing mark by a full minute). It all starts with making a precise exit from the capsule -- something he has rehearsed over and over again -- and he won't have to wait long to hit his top speed.

"If calculations prove to be accurate, and Felix is successful in his attempts to control his position," the Red Bull Stratos site explains, "he will accelerate from standstill to the speed of sound -- that's 0 to approximately 690 miles per hour in 40 seconds or less."

Eventually, Baumgartner will deploy his parachute, at about 5,000 feet above ground, for the final part of his descent. To open that main chute safely, he'll have to have slowed to about 172 mph.

The mission will be well-documented. Here's the array of cameras, including five on Baumgartner himself, that will be recording the ascent and descent:

Baumgartner's capsule is equipped with nine HD cameras, three digital cinematography cameras and three high-resolution digital still cameras. On his pressure suit, he wears five small HD video cameras - two on each thigh and one on his chest pack. In the air the helicopter, which will track both Baumgartner and the capsule, is equipped with a gyro-stabilized Cineflex HD camera and two interior HD cameras. The mission's two ground-based optical tracking systems, which are mobile, each include an HD P2 camera, a 4K camera, a shortwave infrared camera and a digital still camera - with a variety of high-power zoom lenses and large telescopes. To receive the live signals, a dedicated radio communications system had to be set up, including both fixed and mobile units in a range of 200 miles around Roswell.

Baumgartner's jump may turn out to be record-setting, but it's not completely unprecedented. In August 1960, Air Force officer Joe Kittinger set the enduring standard by jumping from 102,800 feet (19.5 miles) and hitting a top speed of about 614 mph. That effort came in the early days of the space race -- eight months before Yuri Gagarin became the first man in space -- as researchers sought to learn whether it was possible for a pilot, or an astronaut, to safely eject at such rarefied heights.

The Red Bull Stratos project lays claim to advancing the science of aerospace safety. "The mission's findings may point the way toward developing escape systems for the space tourists of the future, as well as for the pilots and astronauts who already need suborbital systems today," the site says.

The dangers to the human body way, way up in the stratosphere are legion, from extreme cold to lack of oxygen to the low, low air pressure that could, in effect, cause a person's blood to boil.

Mix in supersonic speed, and the risk only gets that much more outrageous. As Baumgartner told NPR in an interview in May, "Well, mostly, the scientists, they think you cannot maintain your normal freefall position, so [you] would start flat-spinning. 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."

But Baumgartner, an accomplished BASE jumper, is no stranger to extreme skydiving. In 2007, for instance, he jumped from Taipei 101 Tower in Taiwan (1,669 feet), at that time the world's tallest building, and in 2004 he jumped into Marmet Cave in Croatia's Velebit National Park (623 feet deep). He also has used carbon wings to make a freefall flight across the English Channel.