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鈥檚 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鈥檚 heat makes the gas expand. But the balloon will
drop at night when the helium cools and contracts. 鈥淭he 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,鈥� says Steve Smith, ULDB project manager at NASA
Goddard Space Flight Center鈥檚 Wallops Flight Facility in Virginia.
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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. 鈥淭he total thickness is about that of a lightweight garbage bag,鈥�
says Smith.
The superballoon has been dubbed the 鈥減umpkin鈥� because of its odd flattened
shape鈥攊t 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
鈥渋ntermediate-size鈥� 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鈥攁 scientific experiment to observe 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. 鈥淥nce people
realise this is a cheap alternative to satellites, I think we鈥檒l see a host of
novel applications,鈥� says Smith.
鈥淟ong-duration balloons will make a big difference to astronomy, because
they鈥檙e a cheap way to get almost into space,鈥� says John Mather, project
scientist on NASA鈥檚 Next Generation Space Telescope. And Andy Yeatman of the
Meteorological Office in Bracknell says they could beam back useful data for
weather forecasting. 鈥淲e鈥檙e always on the look out for new data for our computer
models of the atmosphere,鈥� he says.