Cryogenic tank research shifts from materials to permeation and cycling

Hydrogen aircraft research has moved past the question of whether composite tanks can hold liquid hydrogen. Multiple centres have demonstrated that. The open problem is permeation over operational life, and the cycling behaviour of liner and matrix under repeated cryogenic contraction.

Permeation matters commercially because a tank losing a fraction of a per cent per hour is unusable on a scheduled network, however impressive its burst strength.

The testing required is unglamorous and slow: thousands of cycles instrumented for loss, which is why so few facilities offer it and why the queue at those that do runs long.

What to watch: which centres publish cycle counts rather than burst-pressure figures. The first tells you a tank is nearly a product; the second tells you it is still a demonstrator.