New Scientist - USA (2019-12-21)

21/28 December 2019 | New Scientist | 69

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 how to make the shell

of a vacuum airship 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 O-Boot

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? ❚

Philip Ball is a science
writer based in London.
He is feeling buoyant
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instance, featured a dining room and

cabins with beds.

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 Flying Whales 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

“ You become like a ship in the ocean, 

but with a port that exists anywhere”