The golden age of airship travel came to an abrupt end in 1937 when the German airship Hindenburg, coming in to New Jersey after a transatlantic flight, collided with its mooring tower and disintegrated in a huge fireball, killing 36.
The images of its huge cigar shape crumpling into a gas-fuelled inferno was enough to convince the world that the aircraft's flammable skin and the vast volumes of explosive hydrogen used to lift the airships made them unsafe.
Today's airships are lifted by helium. But, while helium is a major component of our atmosphere, it is nearly impossible to extract it from the air, which makes it more expensive than hydrogen.
However there are huge naturally occurring reserves of the gas in the United States, Poland, Russia and Canada, and a huge reserve of helium was discovered in Qatar.
Another problem that bedevilled the early airships was buoyancy control. Airships relied on taking on board water or soil as ballast to ensure they stayed on the ground as passengers boarded. It also made adjusting the buoyancy mid-flight relatively difficult.
The prototype airship being built by Aeros will use a new system doing away with the need for ballast to reach the correct altitude and ropes and docking stations on the ground to stop a vessel floating off.
Instead, the Aeroscraft uses large bags, or bladders, inside a rigid structure. When the pilot wants to descend, the vehicle needs to be heavier, so the helium in the craft is compressed into storage tanks.
The vacuum created inside the body draws air from the outside.
As air is heavier than helium, the vehicle sinks. To rise again, the helium is released, pushing the air out of the bags and giving lift. "We can control the buoyancy and allow ourselves to come to the ground and land vertically as well as take off vertically," says Fred Edworthy of Aeros.
