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Technology update
HALE a new airship
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Airships have played a passing role in aviation for close to a century.
Their designers have tried hard to establish them as practical forms of
intercontinental transport or to make them capable of performing special
tasks. But for a variety of reasons that include their public safety
image, airships have never fully met the criteria that would establish
them as a real success. However, now they are under consideration again
by - unlikely though it may seem - the European Space Agency (ESA).
According to the agency, our skies could soon be home to special airships
able to provide local to regional telecommunication services, Earth
observation services, atmospheric science, and astronomical observations.
Working with DaimlerChrysler Aerospace of Germany, Lindstrand Balloons
in the UK and the Technical University of Delft, Netherlands, ESA has
completed a first assessment of a concept for high-altitude long
endurance (HALE) "aerostatic craft" positioned in the stratosphere at an
altitude of about 20 km, with an operational lifetime that may be
measured in years.
The HALE design comprises a large, helium-filled, powered airship with
an aerodynamic cigar shape, measuring about 220 m long and with a
diameter of some 55 m and able to carry a payload of up to 1000 kg.
Unlike Zeppelins, which they closely resemble from the outside, HALEs
do not need a rigid overall internal structure, says the agency. With
modern flexible hull materials, helium-tight and ultraviolet-resistant,
their design can rely on pressurization to impart the necessary stiffness
to the airship body. Only local rigid reinforcement for the engine and
payload attachment is necessary.
HALE requires a high-efficiency electric motor for mobility and for
positioning against stratospheric winds, although these should be
minimal. Solar cells would cover the upper part of their skins to
supply energy for the electric motor that would drive a large propeller.
Energy would be stored for propulsion during the hours of darkness.
According to ESA, Earth observation is a domain in which HALEs can play
an important role in permanent or ad-hoc services such as
environmental monitoring or disaster management.
ESA's interest in HALEs is due to their relevance to a broad range
of space technologies such as thin-film solar cells, inflatable
technology, telecommunication equipment, astronomical instruments and
various subsystems such as power management and distribution, steerable
antennas, Earth observation sensors, and radar imagers. Lightweight
design, another typical area of special expertise, is particularly
important to the development of HALE airships. According to the agency,
this initiative must be seen in the context of similar efforts in
Japan (Sky-Net) and the U.S. (Sky Station International) in which
European space and balloon manufacturing companies are participating.
Stuart Birch
Aerospace Engineering August 2000
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