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Comment by credit_guy | Hacker News Reader

There's actually no need for hydrogen. Helium would do just fine. From the blog post, filling the hypothetical airship with helium would cost $8 MM, while filling it with hydrogen would cost only $100k. Sounds like a no brainer. But, the overall cost of the airship would be at $100 MM. Hydrogen would result in a less than 10% cost reduction.

Now, the FAA approved unleaded jet fuel in 2022. Yes, that's how conservative FAA is. We'll sooner achieve world peace than the FAA would approve hydrogen for airships.

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Helium is a non-renewable resource drilled out of the ground, of which there is a global 'crisis' shortage[1]. Hydrogen is easy to make in vast quantities and cheaper. But more importantly, while they have similar lift capacities on paper (Helium ~90% of Hydrogen), in practice they don't - https://www.airships.net/helium-hydrogen-airships/ has an explanation and calculations.

Hydrogen lift airships set off fully inflated and vent Hydrogen along the way for control of altitude and to stop their lift cells expanding too much as they rise into lower pressure air; Helium is too expensive to vent casually, so they have to start less inflated to protect the lift cells, and other concerns so Helium lift ends up with half the payload carrying capacity, less fuel, shorter flight distances.

And, nb. the deadliest airship disaster was the USS Akron which was was a Helium lift airship which crashed in a storm with 73 deaths and 3 survivors. It's not as simple as Hydrogen = danger, Helium = safe.

[1] https://www.forbes.com/sites/omerawan/2022/11/10/the-helium-...

If fusion power takes off, could you produce helium as a by-product?

if we figured out fusion, it would alter the economics of all of this

why not fusion powered ships/trains/airplanes

> why not fusion powered ships/trains/airplanes[?]

What could possibly go wrong?

We already have fission powered ships and submarines.

We almost had fission powered airplanes and airships: https://en.wikipedia.org/wiki/Nuclear-powered_aircraft

and https://en.wikipedia.org/wiki/Lockheed_CL-1201

And dreams of fission trains: https://twsmedia.co.uk/2020/05/09/atomic-trains/

Sense prevailed, and we do not have civilian mobile nuclear reactors.

The military are mad. Mad and bad. It is in the job description.

We would all be better off if none of them (the military) existed

Afaik what makes fusion hard is maintaining the conditions that allow fusion to occur. Because of this, it’s quite safe - if anything goes wrong, it’ll just stop working.

Safe? Really?

I expect that the containment vessels will get very radioactive.

But all a bit hypothetical, since none exist

Yes they do exist, link elsewhere in this thread, Helion have a 7th generation nuclear fusion reactor fusing once every ten seconds or so. https://www.youtube.com/watch?v=_bDXXWQxK38

(It's not surplus of power, but it is repeatable fusion actually happening).

That is not a fusion reactor

There's a fusion startup called Helion near Seattle working on this, it'll be really exciting if it pans out at scale.

This video was a fascinating watch: https://www.youtube.com/watch?v=_bDXXWQxK38

Basically, no: https://www.jerf.org/iri/post/2922/

And that assumes perfect capture, too.

If you're going that route it'd probably be better to just use hot air with the energy.

Nice! Thanks.

Probably, but the amount would be tiny. ITER is trying to generate 500 megawatt from a half-gram of hydrogen.

Yeah hydrogen sounds like it could even be safer given that you get a larger buoyancy buffer to fight downdrafts? It's a real public misconception that it just explodes from all those oxyhydrogen experiments at chemistry class, but pure hydrogen such as in airships just slowly burns, much like any other fuel we fill our planes with.

The main problem is still that you need to contain a large volume, which will inevitably get pushed around by wind more than you can compensate for.

I wonder if you could use a fuel cell to get power from the hydrogen you'd otherwise vent.

You may have overlooked the part where filling the quantity of airships that would (theoretically) be used would represent over half of the KNOWN quantity exploitable on earth, and would take decades to produce at current production rates. Also, they would need topped up over time. Compared to hydrogen, which is cheap, available, and renewable.

> KNOWN quantity exploitable on earth

It's great that you emphasized "known".

Knowledge is not a static thing. Also what's economically exploitable is a variable thing.

Currently, the US produces 40% of the world's helium, despite producing only 25% of the world's natural gas. Is it because the US has drawn a lucky lottery ticket for helium?

That's very unlikely. Helium is being produced continuously inside Earth as the alpha particles generated during the radioactive decay of some elements (mainly Uranium and Thorium, but Radon too). It seeps upward, and it generally escapes in the atmosphere, but some of it gets trapped in the same geological formations that trap natural gas.

In most places people don't bother to see how much helium there is in natural gas. They just sell the gas and take the money. Separating helium can increase the profitability a bit, but it depends on how cheaply you can do the separation. It's very likely that the US has better technology than the rest of the world, and because of that it separates more helium for the same quantity of natural gas.

As the technology will spread out, more helium will become recoverable.

Also, it may come as a tautology, but more helium is economically recoverable if its price goes up.

The FAA approved modifications to piston engines to use unleaded avgas. Jet fuel doesn’t have lead.

Also, this isn’t about the FAA just being slow for no reason. Switching from leaded to unleaded without the engine modifications was not safe for the piston aircraft that need it.

https://en.wikipedia.org/wiki/Jet_fuel

https://en.wikipedia.org/wiki/Avgas

It's not safe for us to be breathing. But that doesn't matter to cheapskate rich private plane owners or their regulatory-captured FAA.

The really rich private plane owners all have planes that burn jet fuel, which is always unleaded. The piston planes are generally owned by "doctor rich" upper-middle class people, who have political influence to be sure but they're hardly the billionaires that might be known by name to politicians.

I think it's more likely that the FAA protects general aviation because general aviation is part of the professional pilot training pipeline.

The people that are below “doctor rich” just rent their planes from the FBO, a cheap piston plane can rent for $125-$175/hour. So you can get in a couple hours of flying for what it costs a couple to go to a football game.

Nothing is stopping the EPA from banning it regardless of what the FAA wants. The FAA doesn’t regulate emissions.

Author mentioned a market for 25K of these airships, which is like half the helium on earth the first time you fill them up. $8M will go up once you start building

So, if filling your gas tank cost 8% of the price of your car... you'ld think nothing of it? Lift gas leaks (esp He) and gets vented. So this seems odd to me. It's kinda like buying your car again every few months to a year or paying $250/gal to fill up. Now 80x lower at 0.1% of the car price you're in the regime where it's negligible like an EV.

> Lift gas leaks (esp He)

Hydrogen more than helium, I believe.

Each Hydrogen molecule is more reactive, but actually a larger molecule (less leaky) because there are two (it's diatomic H2 rather than monoatomic He).

Now it does get complicated, because the simple atomic radii aren't sufficient when you start bouncing around and leaking through other materials, but suffice it to say that He is still smaller once you look at the Vander Walls attraction and everything. It may only be 10% smaller, but that leads to at least a 20% lower leak rate.

https://bbblimp.com/2021/09/17/helium-vs-hydrogen-atom-size/

Lift gas is a consumable. You have to vent it to descend in many cases, and that’s ignoring the inevitable leaks and diffusion.

> Lift gas is a consumable. You have to vent it to descend in many cases, and that’s ignoring the inevitable leaks and diffusion

Helium blimps compression the gas to lower buoyancy

> Helium would do just fine.

Though that creates another problem: there is a shortage of Helium developing that is starting to cause concerts in a few places (like medical imaging, which it is used as a coolant for devices like MRI scanners). That $8E6 might grow significantly not long after the first airships roll off the production line, and it'll raise for other users significantly too as available supply becomes more contested.

> There's actually no need for hydrogen.

The Hindenburg was originally designed with Helium in mind, but because of a US export ban (at the time Helium was in even shorter supply, and most of it was being produced from resources in the US) forced a redesign.

Unless new practical+affordable sources are found, the same sort of design limitations could strike again.

As a noble gas, helium can't be synthesized, so its cost is because of its scarcity— and because it's a small molecule (like hydrogen), you inevitably lose some and require continuous top-ups.

None of this sounds like it would be realistic at scale, no matter the amount of money in play.

Preventing the helium from leaking out of wherever its stored is challenging, it's not a "fill once and forget about it" kind of deal. Helium is bound to get more expensive too.

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