Up, up (and up, and up) and away

With the advent of powered flight at the turn of the 20th century, balloon flight might have seemed doomed to extinction. However, the practice -- invented in 1783 -- has a new lease on life at the forefront of astronomy.

Astronomers have long preferred to look skyward from above the distortions caused by the atmosphere, but the expense and time involved in the launch and use of space-based Hubble make the use of high-altitude balloons a feasible alternative for astronomers trying to get the astronaut's view, said Danny Ball, site manager of the National Scientific Balloon Facility in Palestine, Texas.

Last month, a group of eight organizations and universities led by Penn researchers sent a two-ton telescope to the very edge of the atmosphere by no other means than a colossal, helium-filled balloon.

The Balloon-borne Large-Aperture Sub-millimeter Telescope project, led by Physics and Astronomy professor Mark Devlin, launched the balloon and device from Sweden and recovered it in Canada four days later.

When on the ground, the balloon -- made by Texas-based Aerostar -- was about 175 feet in height. But due to the decreased air pressure at high altitudes, it expanded as it rose until it had a volume of 37 million cubic feet and, as Ball put it, was as big as the Houston Astrodome. Vents then opened to release excess helium.

At its highest, the balloon reached an altitude of 125,000 feet, Devlin said. By contrast, commercial jets fly between 30,000 and 45,000 feet.

By the launch, researchers hoped to study wavelengths of radiation shorter than a millimeter that are emitted from distant stars. Because of the immense spans that separate the earth and those objects, they appear to observers as they were thousands of years ago.

Devlin said in an e-mail interview from Vancouver that while researchers are still analyzing the data collected during the four-day flight, he expects that "we will learn a great deal about the nature of star formation in our own galaxy."

Still, the project was not without its difficulties. One problem encountered by the researchers was the effect of changing temperatures on helium, which expands and contracts in response to heat and cold. This would have made for a bumpy ride for the telescope as the balloon rose and fell by day and night.

However, Devlin and his team were able to minimize this concern by confining the balloon's path to the far north, where the sun shines all day during the summer.

Additionally, Devlin would not downplay the importance of any conceivable problem, saying that "if [anything] fails in flight, it could trash everything. It's not like we can send a student up with the payload."

Recovery of the telescope and balloon posed its own problems. Said Simon Dicker, a research associate with the BLAST project, "It really does land in the middle of nowhere. You ... have no control over where it lands."

When the balloon did come down over Canada's Victoria Island, the telescope's mirror was cracked, but Devlin's enthusiasm with the overall good result was not much diminished.

Devlin added that another balloon flight is scheduled for December 2006 over Antarctica. That project is intended to gather similar information, but about galaxies other than this one.

However, the BLAST researchers do not intend to use balloons forever. In a few years, Devlin said, a telescope called the Spectral and Photometric Imaging Receiver will capture sub-millimeter radiation from space.

The National Scientific Balloon Facility launches between 15 and 20 such balloons per year. Ball said that they carry instruments to detect gamma and X-rays as well as perform scientific research into atmospheric chemistry.

Devlin said that the BLAST project was financed primarily by NASA, though other contributions came from the Canadian Space Agency and the Particle Physics and Astronomy Research Council. The project cost between $4 and 5 million, not including the launch.

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