NASA floats idea for balloon 'Superpressure' model could soar longer than conventional craft

December 22, 1997|By Douglas M. Birch | Douglas M. Birch,SUN STAFF

GREENBELT -- Engineers at NASA's Goddard Space Flight Center are trying to design and build a super balloon that could keep a ton of astronomical instruments in the upper atmosphere for more than three months, up to 10 times longer than existing lighter-than-air craft.

Today, conventional research balloons typically stay up only 10 to 20 days. The National Aeronautics and Space Administration's new vehicle, called a "superpressure" balloon, would spend at least 100 days aloft, and serve as an ultra-low-cost orbiter that could circle the Earth 10 times.

If the project succeeds -- and there is no guarantee it will -- NASA plans to begin using superpressure balloons to loft X-ray, gamma ray and ultraviolet telescopes by the year 2000.

"If we can make it work, we'll have a flight capability very competitive with space flight," says Jack Tueller, a Goddard astrophysicist who is chief scientist for the Ultra Long Duration Balloon project.

Project engineers see it as an audacious effort to advance balloon technology, the fulfilment of a decades-old dream.

"It's very exciting to me, because it's basically what I've lived for," says Steve Smith, project manager for the superpressure balloon at Goddard's Wallops Island test range on Virginia's Eastern Shore.

But this low-key, low-profile and shoestring project clearly isn't the Apollo program.

Tueller's second-floor office in Greenbelt, which serves as superpressure balloon headquarters, is plastered with family photographs, plaques and sticky notes. He works at an old Macintosh computer. Colleagues drift in and out, picking up papers from a communal printer on a table a few steps from his desk.

Rocket giants Boeing and Lockheed-Martin have no hand in this program. NASA is working on it with the nation's only research balloon builder, Raven Industries of Sioux Falls, S.D.

Testing prototypes of these amoeba-like aircraft consists partly of pumping them up with helium until they pop. Some of that work is being done at the National Scientific Balloon Facility in the East Texas town of Palestine (pronounced Pal-es-teen.)

At NASA, even "low cost" projects can carry price tags of $100 million or more. But development of the super balloon, Tueller estimates, should cost a minuscule $5 million to $10 million -- most of it scraped together from existing budgets. Building and launching it is expected to cost $1 million.

That compares to $18 million for NASA's lowest-cost rocket, the airplane-borne Pegasus.

The first attempt at a 100-day flight is expected in late 2000, and will likely lift off from Australia or New Zealand.

What sets the superpressure balloon apart?

Conventional balloons are open at the bottom, like hot air balloons. A superpressure balloon is sealed and pressurized, like a child's toy balloon.

Unpressurized balloons easily adjust to the dramatic swings in temperature typical of high altitudes. At 30 miles, the thermometer can yo-yo between about 20 below zero and minus 112 degrees Fahrenheit.

When a conventional balloon heats up, the gas inside expands and escapes. This prevents the ultra-thin fabric from ripping. As the balloon cools, the helium inside shrinks. That means the balloon's volume shrinks. And that reduces its buoyancy. To maintain altitude, the balloon must drop ballast.

After heating up and cooling down several times, conventional balloons deplete their reserves of helium and ballast. Gravity takes over.

A long-duration balloon carries a pressurized load of helium in a relatively compact, sealed envelope. It neither expands when heated nor contracts when cooled. In this way, it maintains a constant altitude.

Its fabric skin must be as light as possible, but strong enough to keep from stretching under tremendous pressure or tearing while carrying thousands of pounds of payload.

Two recent advances have made superpressure balloons possible, Smith says.

The first is the development of new lightweight, ultra-strong synthetic materials. NASA is studying two candidate fabrics -- both sandwiches of materials, including "rip-stop" nylon used in many winter coats.

The second important advance is in computer science.

Only in the past eight to 10 years have computer models become sophisticated enough to predict the behavior of the skin of pressurized balloons in extreme environments.

Balloon flights have long been used to test technology that was later sent aloft aboard satellites. An early version of the Hubble Space Telescope flew aboard a balloon in the 1960s.

"The balloon program is really a crucial link in the development of new technology," Tueller says.

Balloons can also be launched on short notice. When a supernova exploded in the Milky Way galaxy in February 1987, no satellites were in position to look at this rare event -- the violent death of a star. Building and scheduling a satellite would have taken at least two years. Balloon-born instruments began making measurements in a few months.

But balloons have their disadvantages.

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