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Balloon

The helium balloon that brought Felix to such great heights! Photo Credit: http://channel.nationalgeographic.com/channel/space-dive/galleries/preparing-for-the-supersonic-dive/at/balloon-blowup-66340/

On October 14, 2012, people across the nation were watching, with pits in their stomachs, as Felix Baumgartner attempted the highest and fastest skydive in history. Certainly Baumgartner got even more nervous as a dispatcher Joe Kittinger declared "There it is; the world is out there...Our guardian angel will take care of you" right before Baumgartner hoisted himself out of the sitting position and began plummeting toward Earth (http://abcnews.go.com/US/felix-baumgartner-supersonic-skydive-swimming-touching-water/story?id=17479415#.UJAuCsXO14s).

Baumgartner fell to his knees and pumped his fists to the air as a sign of victory when he landed safely on the ground after successfully skydiving, quite literally, from the edge of space.

A task such as the one Felix Baumgartner attempted is completely intertwined with Physics. This page is dedicated to discussing the physics regarding the massive helium balloon which brought Baumgartner to 128,100 feet, over 24 miles high into the atmosphere.

Baumgartner reached an incredibly high altitude, significantly higher than the average plane or jet. As altitude increases, the air becomes less dense and the air pressure is reduced. Consequently, the air pressure under an object immersed in a fluid (such as air) is greater than the air pressure on the top of the object. As a result, the buoyant force easily pushes the object upward. The buoyant force refers to "the upward force exerted by a fluid on an object immersed in that fluid," caused by the difference in pressure above and below the object (Louis A. Bloomfield, How Things Work, 4th Edition, Glossary). Archimedes' Principle, a fundamental concept in Physics, states that an object partially or wholly immersed in a fluid is acted on by an upward buoyant force equal to the weight of the fluid it displaces. Clearly, an object immersed in a fluid is taking up space...space which cannot also be take up by that fluid since two things that have mass cannot simultaneously be in one specific location or take up the same space.

The helium balloon used to bring Baumgartner to such great heights is an object immersed in the fluid air; it is exposed to a buoyant force equal to the weight of the air it displaces. This concept is explained by the following equations and diagrams.

Capture

Object immersed in a fluid (in this picture, a basic cube)







Buoyant Force


Buoyancy.svg

A pictorial depiction of buoyancy

Archimedes' Principle makes it known that the helium balloon which carried Baumgartner into the atmosphere was acted on by a buoyant force equal to the weight of the air it displaced. The balloon was filled with helium instead of another gas to create lift, since helium is less dense than air. The helium balloon used was categorically massive, meaning the buoyant force was of great magnitude.

Uninflated, the balloon used weighs 3,708 pounds; it is nearly 30 million cubic feet in capacity. At the time of launch, the balloon was tall and thin; the shape became more round as the altitude increased. This is because the helium slowly expanded as the balloon ascended. Over the course of the mission, the balloon drastically changed shape. At launch, it stretched 55 stories high, 550 feet. Once it reached 120,000 feet into the atmosphere, the balloon was 334.82 feet tall and 424.37 feet in diameter. http://www.redbullstratos.com/technology/high-altitude-balloon/

Material of the balloon: "It is constructed of strips of high-performance polyethylene (plastic) film that is only 0.0008 inches thick. In total, these strips would cover 40 acres if they were laid flat. Polyester-fibre reinforced load tapes are incorporated to do the weight bearing" (http://www.redbullstratos.com/technology/high-altitude-balloon/).

A massive helium balloon calls for a massive amount of helium. The helium was delivered on two large trucks. A "launch arm" was used to restrain part of the balloon during inflation, a process that took between approximately 45 minutes to an hour. Once everything was prepared for launch, the arm released the balloon, enabling it to rise. As the balloon began to ascend, a crane drove the capsule containing Baumgartner (in his space suit and ready for the adventure) under the balloon. As the balloon rose, it lifted the capsule off the crane and the ascent began. http://www.redbullstratos.com/technology/high-altitude-balloon/

Of course, there were many unknowns and risks involved. Balloons are affected by air movement and the thin plastic of the balloon used could be torn by wind. This is one reason the event was postponed due to weather.

The target altitude for Baumgartner was refered to as "float altitude." This is the height at which a balloon's ascent levels off and does not rise anymore. This is because the air density decreases with altitude. "Float altitude is reached when the average density of the ablloon is the same as the density of the surrounding atmosphere" (http://www.redbullstratos.com/technology/high-altitude-balloon/).

This same principle applies to hot-air balloons:

"Even if the pilot heats the air to be very hot, the balloon won't rise upward forever. As the balloon ascends, the air becomes thinner and the pressure decreases both inside and outside the envelope. Although the balloon's weight decreases as the air thins out, the buoyant force on it decreases even more rapidly, and it becomes less effective at lifting its cargo. When the air becomes too thin to life the balloon any higher, the balloon reaches a flight ceiling above which it can't rise, even if the pilot turns the flame on full blast. For each hot-air temperature, then, there is a cruising altitude at which the balloon will hover. When the balloon reaches that altitude, it's in stable equilibrium" (Louis A. Bloomfield, How Things Work, 4th Edition, p. 161). Balloon.capsule

Balloon.liberty

Balloon compared to the Statue of Liberty

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