Balloons Over Antarctica: Multi-Ton Experiments Float Over the Ice Suspended from Balloons

February. The summer season in Antarctica is winding down. Field camps are being pulled in. Groups of scientists are heading north for warmer climes. Just one huge helium balloon is still floating 110,000 feet above the ice. Each year 2 or 3 baseball-field-sized balloons lift scientific experiments weighing tons to the top of the atmosphere. But this lone balloon still floating is different.

Scientific Ballooning over Antarctica

Some experiments spend weeks above 99% or more of the atmosphere without the benefit of a rocket launch. These include cosmic-ray experiments trying to catch high-energy particles arriving from outside our solar system or even outside our galaxy. One even seeks to use the immense ice sheets of Antarctica as gigantic radio-frequency radiators signaling when extremely energetic neutrinos interact. This would form a cascade of charged particles traveling faster than the speed of light in the ice (but obviously slower than the speed of light in vacuum), causing an electromagnetic sonic-boom-equivalent known as Cherenkov radiation.

The advantages for flying over Antarctica are several. First, the summer vortex over Antarctica carries stratospheric balloons in a roughly circular pattern, almost always above land (or ice), making a "splash, glug, glug, glug" ending less likely. Second, at no other latitude on Earth is there a lower risk of "oops," dropping a ton or more on someone's head and ruining their entire day.

A third advantage is that Antarctica is a political no-man's-land, so no over-flight permissions are required from such trusting governments as Russia's or that of the People's Republic of China. Fourth, summer in Antarctica provides the ultimate free lunch, 24-hours-a-day sunlight to power these experiments.

A Breakthrough in Scientific Ballooning - A Super-pressure Pumpkin (Balloon)

The balloons flown over Antarctica each year have been so-called zero-pressure balloons. These balloons are filled with just enough helium to provide about 10% free lift. As the balloons float to the top of the atmosphere the atmospheric pressure around them drops, and the little bit of helium expands.

Reaching float near 130,000 feet (almost 25 miles) they're fully inflated, with volumes as large as 40 million cubic feet. That's big enough to park a jumbo-jet in (if you could figure out a way to get it in without breaking the balloon).

At local midnight in Antarctica, the sun is low over the horizon, reducing the heat radiating on the balloon. As the balloon's helium cools down it shrinks, dropping the balloon by 5,000-10,000 feet. At noon the higher sun angle heats up the helium, expanding it enough to cause the balloon to over-shoot equilibrium height.

The slightly higher internal relative to outer pressure resulting can easily burst the sandwich-bag-thin balloon. To avoid this "pop" some helium is vented out. Recall your heart skipping a beat last time you over-inflated a party balloon until it popped? Now multiply the balloon volume by 40,000,000, add a 2-3 ton package dropping 130,000 feet, trashing years of effort and millions of dollars in cost, and you can see why this is one pop you'd like to avoid. Venting helium however means that next drop/rise altitude cycle would be lower, so ballast must be dropped to compensate.

For nearly a decade NASA has been developing a new type of balloon to avoid this limitation, allowing much longer flights without tons of ballast. These so-called super-pressure pumpkin balloons have been tricky to design and fabricate. This year however, the first large-scale pumpkin balloon was successfully launched by the Columbia Scientific Ballooning Facility staff and is still aloft after more than a month.

The label "super-pressure balloon" refers to its design, intended to withstand a greater internal than external pressure. To accomplish this, the balloon has hundreds of long straps that accept the increased mechanical load. The straps are a bit shorter than half the vertical circumference of the balloon causing vertical indentations similar to a pumpkin's (but better not carve this pumpkin into a Jack-O-Lantern!).

The Future of Pumpkin Balloons - More than a bunch of Hot Air over a Cold Antarctica

Ultimately, NASA hopes to be able to steer such balloons, at which point it could safely let them float for many months, possibly years, even if they stray from Antarctica. This would provide a much cheaper alternative to launching multi-ton experiments into orbit. Can you blame NASA for spending years developing these pumpkin balloons? With launch prices at $50,000 or more per pound, would you like to pay for the next 2-ton satellite launch?