(Engineers abandoned the use of hydrogen in 1937 after the Hindenburg, a German airship, was consumed by flames in less than a minute).
More recently but less perilously, CargoLifter, a German firm that planned to develop a dedicated heavy-lifting airship, went bust in 2002 with only a huge empty hangar and a few blueprints to show for it.Technology Quarterly Splitting the digital difference Behold, the bus of the future Pipe in the sky?
But there is a catch: so far, nobody has ever built an airship so large.
A heavy-lifting airship must be easy to tie down, even in cross winds.
Before building the Hindenburg, which was 245 metres long, the Luftschiffbau Zeppelin company first built more than 120 smaller airships, each slightly bigger than the last.One difficulty, for example, is that if the bow is raised too high above the stern during a climb, the airship can tip into a vertical position.
The Walrus project also took this approach.Before his death in 1917, Count von Zeppelin, inventor of the airship, was hailed as the greatest German of the 20th century.
The arrangements in Athens include: a 70,000-strong security force; an airship packed with surveillance equipment; and gizmo-filled aircraft and ships, courtesy of NATO, which is also providing chemical, biological and nuclear response units.
Such airships will, however, be much cheaper to launch and maintain than satellites and can do things that satellites cannot.Each 75-metre-long airship will be controlled autonomously, and will contain nearly 37,000 cubic metres of helium to keep it and its 1.4-tonne payload aloft, says Michael Molen, Sanswire's chief executive.
They could have other military uses, too: in 2006, Lockheed Martin is due to position a prototype airship over the city of Akron, Ohio, once the centre of Goodyear's blimp operation, as part of an experimental missile-defence system.
A single airship could, says Mr Molen, potentially provide coverage over an area of nearly 800,000 square kilometres, or about the size of Texas.
(The balloon will then follow Zephyr 3 up, so the mission could also break the altitude record for a manned balloon).As Mr Kelleher points out, airship technology is less mature than that of UAVs.
