LZ-N07, a 75-metre semi-rigid design that can carry two tonnes of cargo, or 12 passengers.

ECONOMIST: Pushing the envelope

CL160, a semi-rigid airship, will be the largest ever made, with a lifting capacity of 160 tonnes.

ECONOMIST: Pushing the envelope

But in the vacuum of space the tiny amount of air trapped between them would inflate to create a semi-rigid structure.

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The advantage of this arrangement is that it can be scaled up more easily than a semi-rigid design, since the envelope is not load-bearing.

ECONOMIST: Pushing the envelope

Larger modern airships rely on a semi-rigid design, in which engines and passenger compartments are suspended from a metal keel that runs along the bottom of the envelope and prevents it from distorting under the load.

ECONOMIST: Pushing the envelope