IN 1670, Francesco Lana, a Jesuit mathematician from Brescia, published a small volume describing his various inventions, including a chapter entitled “A demonstration of the feasibility of constructing a ship with rudder and sails, which will sail through the air”. A sketch showed what it would look like: a typical wooden sailing boat, except that the vessel would be suspended below four copper spheres, each containing a vacuum that, being lighter than air, would provide lift.
The idea didn’t fly. No one could make spheres with walls as thin as Lana calculated he would need – and in any case, they would have collapsed from external air pressure as soon as they were evacuated. But maybe Lana was on to something. There is now renewed interest in his vision of airships sailing through the clouds, borne aloft by nothing – and this time we might have the engineering solutions to get them off the ground.
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Airships have already graced the skies, of course. The earliest ones featured simple balloons filled with hydrogen. Their heyday came in the 1920s, when the familiar elongated shape of the Zeppelin carried passengers across the Atlantic in the lap of luxury: the gondola on the LZ 127 Graf Zeppelin, for instance, featured a dining room and cabins with beds.
“You become like a ship in the ocean, but with a port that exists anywhere”
That golden age ended abruptly in 1937 with the Hindenburg disaster, in which 36 passengers died when a Zeppelin caught fire. But the dream of travelling by such elegant airborne means has never faded.
Airships have several advantages over jet aircraft. They are greener, for starters, because they need much less fuel – their propellers might even be solar-powered – and they don’t need runways because they can take off and land vertically almost anywhere. “You become like a ship in the ocean, but with a port that exists in any place,” says Igor Pasternak, founder of Worldwide Aeros Corp, a company based in California that is developing commercial rigid-shell helium airships for freight transport.
Pasternak isn’t alone in betting on helium airships. French company is developing them for cargo transport, and several other firms are working on “hybrid” airships that incorporate components from winged craft and helicopters to achieve lift both from buoyancy and aerodynamics.
The trouble is that Earth’s helium supply is dwindling and the gas is too expensive to make airships viable on a large scale, says Julian Hunt at the International Institute for Applied Systems Analysis in Laxenburg, Austria. What’s more, maintenance gets very complicated, says Pasternak, because you need systems to control the ballast. Unloading cargo from a freight airship, for example, creates lift that must be counteracted by removing and recompressing some of the helium. That requires devices like valves and pressurised storage compartments, and the more moving parts there are, the more there is to go wrong.
There are no such problems with a vacuum. “I can just open my valve [to let in air] and balance the pressure inside,” says Pasternak. “And if I want to fly, I just start pumping air out again. You can create the lift at any moment.” As a result, Pasternak believes that if we can get vacuum-based vessels aloft, they “will make cargo airships absolutely practical, effective and inexpensive”.
There is a problem, though. Without anything inside an airship’s shell, the air pressure is enormous. Use today’s materials to make a shell strong enough to resist the compression and it will end up so heavy that the vacuum inside will be unable to lift it. Hunt speculates that light yet superstrong carbon-based materials like graphene and carbon nanotubes could overcome this difficulty.
Ben Jenett, working on his doctorate at the Massachusetts Institute of Technology’s Center for Bits and Atoms, has another solution, and he has already made progress towards it.
Jenett has devised lightweight “lattice materials” in which tiny, rod-like struts are assembled into frameworks with tremendous stiffness and strength. It is the same principle as that behind the familiar triangular truss structures in cranes and the Eiffel Tower. Jenett’s struts are linked to form octahedral units with eight triangular faces that can be assembled into extended lattices. They are extremely light without sacrificing strength. A 10-centimetre cube of this lattice material weighs just under 6 grams, about as much as a small strawberry.
What’s more, Jenett believes that the otherwise laborious assembly process can be simplified by using small robots that climb over the framework to put each piece in place.
An empty shell
Jenett has sketched out from a material like this. Working with Christine Gregg and Kenneth Cheung at NASA’s Ames Research Center in California, Jenett calculated that, even with currently available materials, a shell with a thickness one-tenth of the radius of the sphere it contains should be able to withstand the air pressure without buckling. There would also need to be some thin, impermeable skin covering this latticework shell, which would add a bit to the weight, but not enough to invalidate the findings. “A proof-of-concept prototype of at least a portion of this substructure is in the works,” says Jenett.
The challenge is less severe if you create the vacuum only once the ship has reached high altitude, where the air pressure is lower. In that case, Jenett suggests that the initial lift could come from hot air, heated by sunlight. That buoyancy would decline as the external air pressure diminishes, but then air would be pumped out of the airship’s vacuum compartment to generate further lift. “At an operating altitude of 20,000 metres, the airship would be stable using only a near-vacuum environment to generate lift,” he says.
This isn’t just a sketchbook dream. Jenett and his collaborators are in discussion with aeronautical company Aurora Flight Sciences, recently acquired by Boeing, which is interested in developing vacuum balloons for atmospheric satellites. NASA is also considering the lightweight lattice materials for space-based solar arrays and telescopes, and for making pressurised shells in near-vacuum conditions outside that could be quickly assembled by robots for human space settlements.
But thoughts of vacuum airships are in the air. A nascent Italian company called has drawn up ambitious plans, although at this point, they aren’t much more than that. The firm’s hybrid design would allow it to achieve vertical take-off, either via its wings and helicopter-like propellers, or by using helium that is gradually compressed as the ship rises.
“As the external air pressure decreases, the vacuum balloons will be emptied more and more to lighten the load on the wings and reach higher altitudes,” says O-Boot’s CEO Ludovico Turinetti. Propulsion would come from solar-powered electric motors, soaking up sunlight well above the cloud layer.
One way or another, the age of the airship will return, says Pasternak: “The question is when.” The market for freight transport is clear: a fleet of small, cheap airships could make deliveries straight from the factory, without any need for warehouse storage. “If you can establish a carbon-neutral air infrastructure for moving materials and goods, it could be a significant benefit to the environment,” says Jenett.
What about passenger travel? Airships will always be slow compared with jet aeroplanes, so it is hard to see them working for long-distance travel – unless a leisurely, luxurious journey is the whole point. For short trips, though, the speeds would be competitive. People don’t tend to fly for journeys of a few hundred kilometres; the competition is then with trains or cars, which are generally no faster. Airships could be ideal for hopping between islands too, replacing ferries.
And let’s be honest, who wouldn’t be tempted by the chance to travel by gondola, hanging thousands of metres above the ground, borne aloft by nothing but nothing?
