SUPERBALLOONS, which can float for months at a time on the edge of space, could one day take over some of the work of satellites and for less than a tenth of the cost. NASA will test a prototype next March. It hopes to launch its first working balloon by the end of 2000.
The new superballoons are being developed as part of NASA's Ultra-Long Duration Balloon (ULDB) project. They are designed to overcome a fundamental technological shortcoming of existing helium-filled balloons.
The pressure inside and outside the balloon has to be kept equal to prevent stresses ripping the fragile envelope. However, the balloon must lose helium during the day when the sun's heat makes the gas expand. But the balloon will drop at night when the helium cools and contracts. "The only way to maintain altitude is to dump ballast, limiting the time aloft to a maximum of 3 to 5 days at the latitude of the US," says Steve Smith, ULDB project manager at NASA Goddard Space Flight Center's Wallops Flight Facility in Virginia.
With the help of companies in the US and Japan, NASA has developed a lightweight material that is strong enough to withstand the pressure without venting helium. The fabric has three layers bonded together. The outer layer is woven polyester fabric, with a middle layer of mylar and an inner layer of polyethylene. "The total thickness is about that of a lightweight garbage bag," says Smith.
The superballoon has been dubbed the "pumpkin" because of its odd flattened shape-it is 79 metres high and 128 metres in diameter. It will be able to carry a 1-tonne payload at an altitude of 36 kilometres for up to 100 days. The total cost will be up to $3 million.
Raven Industries of Sulphur Springs, Texas is now making an "intermediate-size" balloon. After test flights, the plan is to fly a full-size balloon in December. This will be followed by the first flight with a payload-a scientific experiment to obs-erve cosmic rays.
Smith says the balloon will be ideal for both astronomical and atmospheric experiments. It will be able to carry experiments that are too heavy or too large to fit into a rocket nose cone. Smith also says such balloons could be used to relay voices round the world for mobile phone companies. "Once people realise this is a cheap alternative to satellites, I think we'll see a host of novel applications," says Smith.
"Long-duration balloons will make a big difference to astronomy, because they're a cheap way to get almost into space," says John Mather, project scientist on NASA's Next Generation Space Telescope. And Andy Yeatman of the Meteorological Office in Bracknell says they could beam back useful data for weather forecasting. "We're always on the look out for new data for our computer models of the atmosphere," he says.
Author: Marcus Chown
New Scientist, issue 5th Dec 98
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