Cosmic-Ray Research Above Antarctica

Far above Antarctica, 120,000 feet and more, near the very top of the atmosphere, three enormous balloons float, each large enough to hold a major league baseball field. Forty million cubic feet of low pressure helium - enough to loft 3 tons of scientific equipment over 3 times as high as most modern airliners fly. How did they get there? More importantly, what on Earth for?

Getting Ready for Launch

Three science crews arrived on the Ice in October and November of 2007. Each crew received cargo from "back home." The crews re-assembled their complex instrumentation, and carried out intricate tests over the following weeks. The tests were designed to ferret out any last minute glitch that might render months and years of hard work worthless.

Each instrument team in turn brought their payload to the ultimate point - the declaration they're "flight ready." From this point on it was all up to the weather. The teams eagerly waited for good news about the polar vortex.

A Waiting Game

At altitudes up to 140,000 feet above Antarctica the winds set up each summer, swirling counter-clockwise around the South Pole at speeds of many tens of knots. These are the winds scientists count on to keep research balloons above the Ice. Until this vortex sets up around the pole, anyone launching a balloon runs the risk of losing the payload over the Antarctic Ocean.

Finally the polar vortex set up. The teams attentively listened each day to the local meteorologist's weather briefing. It is his responsibility to predict when a launch window opens and how long it's likely to last. The first launch attempt of the 2007 season was scrubbed - an unexpected change in wind direction and strength made launch impossible. Several more days went by, with the crews anxiously waiting for calm at the surface and slow winds at altitudes up to 5000 feet.

A Picture Perfect Launch

Finally, the day arrived.

December 19^th, 3:30 AM local: The first crew leaves McMurdo Station for Willy Field. Another flurry of preparations and last minute test procedures ensues. Finally, the word goes out - the payload is to be moved to the launch pad. "The Boss" - the launch vehicle for Antarctic balloon payloads trundles slowly bringing the Cosmic Ray Energetics And Mass¹ payload into position. The Columbia Scientific Ballooning Facility (CSBF²) team rolls out the flight train and balloon and attaches them to the payload.

11:00 AM: Balloon inflation begins as helium is pumped into a "bubble" at the top of the balloon.

12:30 PM: the balloon is finally ready. The command goes out over the hand-held radios - launch! The tear-drop shaped balloon is released and quickly lifts until it's vertical and picks up the multi-ton weight of the payload. The launch vehicle releases its grip and the instrument is off, rapidly ascending. A perfect launch!

6:30 PM: the payload reaches its designated float altitude of 127,000 feet. At this altitude the pressure is low enough for the small amount of helium to fully inflate the balloon, which assumes its final spherical shape. The combined science and support crew has now been up for over 15 hours. Nonetheless, this is what we're there for. The high voltage systems are turned on, and instrument tuning begins.

December 20^th, early morning: After hours of tuning, control is handed off to the state-side crew. The time has come to tear down the temporary control center on the Ice and pack it for shipping back home. More than 24 hours after starting, we head back to McMurdo Station. A quick breakfast, an even quicker shower, and finally some sleep.

Heading Home - Or Maybe Not?

That night, at half past midnight we headed out from McMurdo to catch our flight home, the last flight off the continent before Christmas. A last-minute snow storm nearly scrubbed the flight, but we were lucky, and a short break in the weather allowed the C-17 cargo jet to land. Ten minutes after it landed the wind picked up and visibility dropped to 200 feet. Despite some anxious moments, the US Air Force Air Mobility Command jet finally took off. Five hours later we were in New Zealand.

Forty hours after initial takeoff, including 25 hours in the air and 15 hours at various airports, we were finally home. Meanwhile, the balloon was still aloft, the instrument still sending valuable scientific data via the Telemetry and Data Relay Satellite System, and ultimately back to the control center at the University of Maryland.

Cosmic Ray Research

Before the month was out, the remaining two payloads were launched. The Balloon-borne Experiment with Superconducting Solenoid (BESS³), and the Advanced Thin Ionization Calorimeter (ATIC⁴) both launched without a hitch. For the first time ever, three balloons floated at the same time high in the Antarctic sky, carrying three high-energy cosmic-ray experiments. By early February 2008 all three payloads completed their flights, landed, and were recovered as far as practical.

High Energy Cosmic-Ray Experiments measure the sub-atomic particles that arrive from beyond the solar system. Instruments measure the identity of particles going through them, and their energy. These data allow the reconstruction of elemental spectra, giving hints allowing scientists to determine the source of these particles, how they were accelerated to near the speed of light, and what they go through during their 100,000 - 10,000,000 year journey.

Why Antarctica?

One might wonder why a physicist studying cosmic-ray particles would have to travel to the bottom of the world. After all, these particles hit the atmosphere everywhere. The answer is simple. To measure cosmic-ray particles directly, experiments must be flown as high as possible. The Earth's atmosphere acts as a huge radiation shield. This is very good, considering that without this shielding we'd be fried. However, making accurate scientific measurements requires going outside the shield. Enormous helium-filled research balloons loft experiments to altitudes over 125,000 feet - altitudes attained by very few man-made artifacts. In fact, those objects that do go this high are usually placed in orbit or head out to the reaches of our solar system.

High energy cosmic-ray research requires flight durations of many weeks, best done over Antarctica. During the Antarctic summer the constant sunlight provides power via the solar arrays. Flying around the South Pole, balloons stay above solid surface, making successful recovery more likely. By international treaty, Antarctica is not part of any sovereign nation so no over-flight clearances are required from skittish foreign governments.

Finally, and most important, NASA rules require that balloon payloads only be flown where the risk of anything falling kills someone is less than one in a million. This precludes flying balloons over major cities. Given the lack of trajectory control, Antarctica provides a natural solution.

University Research - an Unlikely Path to Adventure

While few would consider years of graduate education in physics as a path to adventure, experimental cosmic-ray researchers travel nearly annually to Antarctica, the final wilderness of our planet, to carry out their work. Some even spend days at remote field camps with no heat and little shelter, hundreds of miles from any base, in places where quite literally, no human had ever set foot before. In a land where life is rare, the only hunt allowed is the hunt for knowledge.

¹cosmicray.umd.edu/cream/
²www.csbf.nasa.gov
³www.universe.nasa.gov/astroparticles/programs/bess/
⁴atic.phys.lsu.edu/aticweb/