In the novel/film Contact the character S.R. Hadden lives in an airliner that rarely lands. With a larger Phoenix that lifestyle could become available to somewhat less wealthy billionaires. Maybe it could eventually become an atmospheric variation of seasteading.
You’d still have to buy the helium (how else does it get off the ground?). Probably more if you intend to safely bring it back down.
So now you have to have at least 2 times the helium needed to attain buoyancy, plus mechanisms to generate hydrogen and vent/replace gas. And systems/procedures to handle edge cases.
It sounds like a lot of complexity and cost added. However, it might be worth it if extremely high altitude is needed. The altitude ceiling could be increased significantly (not sure how much, but <2x) for a given configuration and payload.
It's like a miniature version of the Venus cloud city idea, but here on Earth.
Like rocket stages but for airships.
Does it matter for an unmanned vehicle? Such a thing could be inflated at a safe distance. In some cases, being able to self destruct is a safety benefit (to prevent crashes when control is lost) and a security benefit (to prevent analysis of captured aircraft). Particularly UAVs are popular in military / spying operations.
Helium wins out on the inertness, but has far lower lifting capacity, and of course has a supply issue.
Hydrogen wins on lifting capacity, supply is not an issue at all - but it has a weird image problem, thanks to one singular accident - which was arguably not caused by the lifting gas!
Prior to that accident, hydrogen had a fairly great record with airships, and it was used extensively for ballooning as well without many incidents.
Hydrogen by itself isn't flammable - you need another particular gas involved for that to be an issue. You also need a source of ignition.
See Figure 2, Gas Permeability of Mylar vs. Temperature
Helium permeates Mylar significantly faster than hydrogen over the full temperature range tested. It looks like the helium permeation rate is nearly double that of hydrogen near room temperature. Surprising! I would have guessed that lighter gases permeate faster. Note on the same figure that oxygen permeates faster than nitrogen even though it's heavier.
There is more tabular data here:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/196900...
It confirms the same trend. Helium permeates Mylar faster than hydrogen.
* https://en.wikipedia.org/wiki/Lighter_than_air#Hydrogen_and_...
Agreed that the danger of hydrogen is less than perceived. In an accident it goes up which is normally where the people are not. When it burns it doesn't create much radiant heat. Outdoors in the daytime firefighters have to use something like a broom to find hydrogen fires. Otherwise you could just walk right by one ... which is an issue if you instead walk right into the fire.
We already run into issues with water without cracking water vapor and venting hydrogen into the atmosphere at scale. I shudder at the thought of unconstrained industry being cut loose with the idea that we have an essentially limitless supply without sitting down to really figure out the numbers.
Never mind the maintenance issues. High levels of electrical generation/storage +volatile gas generator? What could possibly go wrong? Hydrogen embrittlement, high level of oxidative stress, increased radiation exposure...
Mean-time-to-failure is not giving the magic 8 ball warm fuzzies. Could be super neat for meteorological/astronomical purposes/reconnaissance purposes though.
I can see the international incidents rolling in now.
"North Korea protests American Weather Baloons"
"Russia introduces new anti-balloon laser"
"China threatens Taiwan over balloon based infrastructure"
Unfortunately, I wouldn't put it passed ad companies to utilize this "exciting new breakthrough in audience outreach" as well.
I'd really like to look at this kind of stuff how I used to as a kid again. Too much time in the tech industry has absolutely ruined my outlook however.
Hydrogen is still expensive to split from water, and the quantities required for deleterious effects to present are so high, that these are really distantly hypothetical "what ifs".
1d-compressium, 1d-tensilium, and 2d-tensilium are all allotropes of obtainium, being the materials with the highest uniaxial compressive strength to mass ratio, the highest uniaxial tensile strength to mass ratio, and the highest biaxial tensile/shear strength to mass ratio. Currently, those are probably diamond struts, buckytube fiber cables, and graphene sheets.
Throw 2d-tensilium envelope around a tensegrity frame with 1d-compressium struts and 1d-tensilium cables. Pump out the interior gas until it breaches or collapses.
Start over. This time, put another frame and envelope around the first, and anchor them to each other with more 1d-tensilium cables. Pump out the interior gas of both pockets until the outer shell breaches or collapses.
Repeat, until the pressure differential on every envelope and shell is insufficient to breach the envelope or buckle the frame. Now you have a gradient from vacuum to atmospheric pressure instead of a perfect vacuum in the whole volume, but you don't have to find any unobtainium to build it.
As a bonus, you can put the envelope on the inside of the shells, and follow a similar process of breaking each one with air, to make an inflatable spacecraft hull that can hold 1 atm of breathing gas on the inside without rupturing in vacuum, using minimal mass.