Red Bull Stratos helium balloon during unmanned test in January Joerg Mitter/Red Bull Media House

The Red Bull Stratos team had been through delays before but Tuesday's live webcast showed the world just how delicate the helium balloon that Felix Baumgartner is relying on to take him up to 120,000 feet really is.

For many people, the idea that a helium balloon can take a person up to the stratosphere was a new one. But then again, there has never been a balloon quite like the one used by the Red Bull Stratos team. Once twisted, as it was by the wind Tuesday, it is no longer safe to use.

Right now, the team has only one left, which will be used Sunday morning, if weather conditions remain stable. The team, however, is in the process of trying to procure a third balloon. Here are some answers to questions you may have on your mind...

nullJoerg Mitter/Red Bull Media House

What is Felix Baumgartner’s balloon made of?

The balloon is constructed of nearly transparent polyethylene (plastic) strips about the same thickness as a dry cleaner bag, which are heat-sealed together.

Why use such a delicate material?

A very large balloon is needed to carry the Red Bull Stratos capsule (which weighs nearly 3,000 pounds) to the stratosphere. Very thin material is necessary to save weight. As it is, despite the light weight of the polyethylene, there is so much of it (40 acres) in Felix's balloon that uninflated it weighs 3,708 pounds.

What is the balloon filled with, and why?

The balloon is filled with helium. Helium is lighter than air, providing the lift needed to take a heavy payload to the stratosphere.

How is a helium balloon different than hot air balloons used for sightseeing?

They're different in many ways, including size, material and construction methods, but perhaps most significantly, using helium for lift allows a higher altitude. A hot-air balloon is limited because the air inside must be heated (usually via propane burners) to provide lift -- and with low oxygen in the upper stratosphere such heating wouldn't be feasible. Helium is lighter than air and provides lift without heating.

nullRed Bull Stratos Team announced the new launch window on October 10/Joerg Mitter/Red Bull Media House

How much helium is used?

The team will insert about 180,000 cubic feet of helium at launch. As the balloon rises and the air pressure decreases, the helium will expand until the entire capacity of nearly 30 million cubic feet is completely full.

That's 10 times larger than Joe Kittinger’s balloon in 1960, and three times bigger than the largest balloon ever launched with humans aboard (project Strato-Lab in 1961).

What are the dimensions of the balloon?

The length of uninflated balloon before launch is 592.41 feet. The height of balloon at takeoff is 550 feet. The takeoff height from the top of balloon to bottom of capsule is about 750 feet. Size of balloon at 120,000 feet: height: 335 feet, diameter: 424 feet.

What kind of weather conditions are necessary to launch such a large balloon?

The factor that concerns the team most is wind. Winds must be no more than about 2 mph from ground level to about 800 feet.

What else are these kinds of balloons used for?

Helium balloons are used by government and university programs to launch weather equipment and telescopes that look into deep space, and also to provide near-space testing of components in preparation for eventual space missions. They are usually custom made, so there are very few in existence.

Can anyone fly a helium balloon?

No, a special license is required.

nullJoerg Mitter/Red Bull Media House

What happens to the balloon after Felix's jump is complete?

When Mission Control determines that the balloon is over an appropriate area, the capsule is remotely triggered to detach from the balloon. The balloon is automatically torn by a cable as it separates from the capsule, so the helium, which is nontoxic when vented into the atmosphere, escapes and the empty balloon envelope falls to earth.

A field crew retrieves polyethylene material, a process they've compared to “wrestling an elephant.” The balloon team also retrieves a digital logger to analyze data from the mission, which can help to inform future flights.

Who launches the balloon?

The balloon launch crew is from ATA Aerospace, a company with a half-century of experience, including support of some of Joe Kittinger's missions. ATA Aerospace is trusted to launch U.S. Air Force high-altitude balloon projects, and collectively the crew members for the Red Bull Stratos balloon have the experience of thousands of balloon launches.

Key among them are crew chief Ed Coca, who directs the team on the runway, and project lead Tracy Gerber, who coordinates balloon launch operations from Mission Control.


Be sure to watch Felix Baumgartner make history Sunday morning -- pending weather conditions -- on the Red Bull Stratos live webcast. Follow Red Bull Stratos and Red Bull on Twitter for more updates.



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