Floating at the Edge of Space

Scientific balloons are often the vehicle of choice

By Karl Hill

When it’s summertime in Antarctica, the ballooning is great.Two ambitious research collaborations found that to be the case a few months ago, when scientific balloons launched from McMurdo Station, Antarctica, carried their experiments to the edge of space.

“These flights turned out to be perfect,” said Danny Ball, site manager for the Columbia Scientific Balloon Facility, which is managed and operated for NASA by New Mexico State University’s Physical Science Laboratory.

One of the flights carried an experiment known as BLAST, for Balloon-borne Large-Aperture Submillimeter Telescope. This international collaboration, led by the University of Pennsylvania, is seeking a better understanding of the early evolution of the universe, when stars and galaxies were just beginning to form, Ball said.

From its balloon-borne vantage point about 120,000 feet above Earth, the BLAST telescope took large-area surveys at submillimeter wavelengths – measurements that should help answer important questions about the formation and evolution of stars, galaxies and clusters of galaxies.

“It looks like the instrument performed very well and it was up for about 11 days,” Ball said. The experiment was brought back down when it ran out of the liquid helium needed to cool the detectors to a temperature near absolute zero.

The other flight, carrying an innovative high-energy neutrino detector dubbed ANITA (Antarctic Impulsive Transient Antenna), stayed aloft for 35 days, circumnavigating the South Pole and the continent of Antarctica two and a half times, Ball said.

ANITA, a collaboration led by a University of Hawaii scientist, uses the entire Antarctic ice sheet as a collecting aperture for detecting high-energy neutrinos – elusive particles that are believed to originate from cosmic ray collisions.

“They are flying a set of sensitive radio receivers with omni-directional antennas that look down at the surface of the ice in Antarctica,” Ball said. “That becomes the telescope; if a neutrino hits that big deep layer of ice it creates a radio signal from which you can draw conclusions about the neutrino.”

For this type of science, the size of the detector is important, Ball noted, and this technique creates “an enormous collection device” about 300 miles in diameter.

The BLAST and ANITA scientists are among the many who recognize that, far from being outdated, scientific balloons can be the most efficient and economical route to some types of space research.

“Ballooning is viewed as a best-value proposition by many scientists,” said Stephen Hottman, associate dean for research and development and deputy director of the Physical Science Laboratory. “A balloon can place an experiment in essentially a space environment in a relatively short time after the inception of an experiment and at a low platform cost.”

Balloons offer scientists the advantage of carrying instruments to altitudes of about 30 miles – above 99.5 percent of the Earth’s atmosphere and free of the distortion it causes – at a fraction of the cost of launching a satellite into orbit. A typical satellite mission can cost about $100 million, compared with $1 million or less for a balloon flight, Ball said.

Ball, a veteran of 27 years with the scientific balloon program, said the advent of long-duration flights is the biggest change in his experience – and ultra-long-duration flights will be the next major advancement.

“We used to be lucky to get 35 hours and now we can fly 35 or 40 days at a time,” he said. The record for duration, a 42-day flight, was launched from Antarctica in December 2004.

PSL is working with NASA’s Wallops Flight Facility in Virginia to develop super-pressure, ultralong- duration balloons (ULDBs) that could stay aloft for 100 days or more. In addition to keeping scientific experiments up for longer periods, ULDBs would open the door for new applications, such as constellations of balloons that could be used for communications.

ULDBs use a closed, super-pressure system that allows them to maintain a constant altitude night and day. With traditional zero-pressure balloons, the gas that carries them aloft contracts when the sun sets, causing the balloon to lose altitude. Ballast can be dropped to offset this effect, but these night-and-day flights can be sustained for only a few days.

In Antarctica in the summer, however, the sun never sets. That’s the season for the balloon program’s annual long-duration flight campaign.

“Our guys go down in late October and come back in late January,” Ball said.

The Columbia Scientific Balloon Facility is based in Palestine, Texas, and also operates out of Fort Sumner, N.M., in addition to launching balloons from Antarctica and sites around the globe.

PSL first won the NASA scientific balloon contract in 1987 and has successfully defended it four times in competitive bid processes. The current 10-year contract, worth a total of about $258 million, is in its fourth year.

http://www.psl.nmsu.edu/aasd/ballooning.php