Skydiving is dangerous -- but not nearly as dangerous as skydiving from a plane in outer space.
That can kill you. The temperature can freeze your body, and the lack of air pressure can boil your blood.
Nonetheless, an Austrian daredevil named Felix Baumgartner plans to take the 23-mile plunge from the edge of space. And in the process, he hopes to become the first parachutist to break the sound barrier, plummeting toward the ground at 760 miles per hour.
But this is no stunt; it's called the Red Bull Stratos project, and the engineers and scientists behind this attempt to break the record for the highest freefall ever -- from 120,000 feet above sea level -- hope it will yield volumes of data that will be used to develop advanced life support systems for future pilots, astronauts, and even space tourists.
And to do it, they've designed a unique supersonic spacesuit.
No one else has tried to use a pressurized suit as Baumgartner plans to; they're typically used to protect jet pilots who eject from their seats -- not skydivers who plan to travel faster than sound.
"So we reconfigured the arms and legs on his suit," says Daniel McCarter, who is building the suit at the David Clark Company, which has developed protective suits -- called PPAs or pilot protective assemblies --since 1941. The company made the first suits to prevent World War II fighter pilots from blacking out during high-acceleration maneuvers, not to mention launch entry suits for space shuttle astronauts.
The changes being made to Baumgartner's suit will allow him to dive with his head at a 25- to 35-degree angle and to control his speed. Full pressure suits for pilots are generally configured for comfort in a sitting position, but "for Felix it's in an almost standing position," says McCarter. The shoulder areas also have to be more flexible, and the designers had to ensure that there will be no "binding up" that could prevent him from making critical maneuvers in freefall.
The suit will essentially be Baumgartner's life-support system, providing oxygen, telemetry, communications and, most importantly, enough pressure to keep him alive. To do this, the suit contains devices known as aneroids, which act like mechanical bellows and respond instantly to changes in atmospheric pressure. When they sense low air pressure, the aneroids trap air in the suit, which then becomes pressurized, squeezing the wearer.
The pressurization is essential: above 63,000 feet, the lack of air pressure makes it not only difficult to get oxygen into the lungs (which would cause Baumgartner to black out), but it also makes it easy for nitrogen bubbles to escape from the blood, causing an embolism and death. Baumgartner's suit will maintain 3.5 psi of pressure -- not so tight that he can't maneuver his arms and legs, but enough to keep nitrogen bubbles from killing him.
"It feels like getting into a sleeping bag with arms," says McCarter. There's a nylon comfort liner, then a ventilation system that keeps the wearer cool. Next comes the pressurized gas layer, followed by a hand-woven layer called the link net that maintains the shape of the suit. Finally, there's the outer, flame-retardant layer made of the heat- and flame-resistant fiber Nomex.
Team members declined to reveal the cost of the suits (there are three: the original prototype, the one Baumgartner will wear, and a backup), except to agree that the Red Bull Stratos project is a multimillion-dollar effort.
So what will it feel like when Baumgartner opens the hatch of the gondola suspended below the weather balloon that will take him to space, and he steps out into 23 miles of nothingness?
"For about the first 30 seconds he's not going to feel anything," says Mike Todd, a life-support engineer at Sage Cheshire Aerospace and a member of the Red Bull Stratos team. This is particularly dangerous because, even though the air is so thin that it won't feel like he's even falling, Baumgartner must get into exactly the right position -- the so-called delta position -- to attain the speed he wants and survive the five-and-a-half-minute descent.
Todd expects Baumgartner will reach Mach1 somewhere between 100,000 and 90,000 feet. But it won't be overly uncomfortable. At that altitude, he says, "It will feel like putting your hand out the window of a car going 35 mph."
McCarter is convinced the suit will protect Baumgartner, based on pilots who have survived ejections at similar altitudes
But exactly what will happen when -- if -- Baumgartner becomes the first supersonic man remains unknown. Could the sonic boom damage his hearing? Will the turbulence of breaking the speed of sound spin him out of control? Will there be any turbulence at all?
"... we don't know what's going to happen," Todd says. "We'll try and push him through it as quickly as possible, but once he steps out of that hatch, he's going to be on his own."
John R. Quain is a personal tech columnist for FoxNews.com. Follow him on Twitter @jqontech or find more tech coverage at J-Q.com.