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Comment by triplesec | Hacker News Reader

I think a big problem is that helium is a very scarce Resource and which we get only from fossil fuels. Much helium has been wasted in the past couple of decades and prices of it will only go up as its scarcity increases. It's really highly needed for medical equipment and other things and I can't see it being used in bulk for this purpose.

Now using hydrogen has been mooted, using newer technologies to keep it safer. I love this idea mentioned in this thread of a vacuum glimpse as well

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But you don't actually expend the helium. You lose a tiny bit through leakage. In airship companies today, the helium is the least of the problems.

I'm not sure that's true. While abundant in the universe, there's a fairly finite amount of helium here on Earth, and once it escapes, it leaves into space for good. The US even has a strategic helium reserve. The shortage of helium was reported back in 2012 [1] We really need that helium for things like MRIs and chip lithography processes.

[1] http://www.popularmechanics.com/science/health/a4046/why-is-...

We still use helium for children's balloons. It's cheap enough that most companies don't even bother to distill it out of natural gas.

I refer you to this article by a chemistry professor: https://www.chemistryworld.com/opinion/helium-in-crisis/3007...

This might be true, that you don't lose much, but every day they'd need recharging a bit, and even without dirigibles, we have barely a century of supply. That is not much. The market rate is criminally low. https://priceonomics.com/the-increasing-scarcity-of-helium/

Well, I agree Congress's elimination of the Strategic Helium Reserve was criminally stupid. I was addressing the cost point, though. Helium is still reasonably cheap, so it's lost in the noise, financially speaking.

Hot air is also completely viable and in many ways simpler to work with, though you need very high temperature or the volume gets extreme. However the most reasonable option is probably multiple layers with hydrogen inside a nitrogen envelope which makes small leaks a non issue.

The numbers don't work for hot air. You just can't get the lift.

It's altitude and temperature dependent. 100 °C Which is normal hot air balloon temperature. If the outside temp is 27c that's 1-(300/370) or 19% lighter than air vs heliums 1-1/14 = 93% lighter than air. But you lift increases significantly with temperature. The downside is you end up spending fuel to add heat. But hot air balloons also have terrible insulation.

Further volume has great scaling if you save 93% with hydrogen having 4x the volume means being ~20% lighter than air provides the same lift.

Now yes scaling the airframe adds weight and drag as does the fuel to provide all that hot air. But you can also significantly past 100c before you encounter massive issues.

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