Don't we have Helium anyway?
What we have naturally comes from radioactive decay deep in the earth. This will continue for some time, but it's a fixed, slow rate.
Helium evaporates into space. Once it's gone, it's gone for good.
The other options we have are hydrogen (extremely reactive), heated oxygen (also reactive), methane (reactive), ammonia...
It's a hard problem.
https://physics.stackexchange.com/questions/71027/is-it-poss...
Nitpick: So is hydrogen.
More precisely, helium is an element that doesn't readily form compounds. Hydrogen does, and as such can be extracted from, say, water via electrolysis.
The secondary issue with helium is that it's much lighter than air -- this is why helium and neon are both much rarer than, say, argon (which is actually the third-most common element in the air after nitrogen and oxygen).
Actually, hydrogen is lighter, and so a better lifting gas, than helium.
He: 0.1786 kg/m^3
H: 0.08988 kg/m^3
Air: 1.225 kg/m^3
Air vs He: 1.0464 kg/m^3
Air vs H: 1.13512 kg/m^3
To put it differently, for helium, the lift is about 86% of the weight of the displaced air, while for hydrogen it's 93%.
Both very good, and both are much better than hot air!
(which gives a lift of only about 25% of the weight of the displaced air, at typical temperatures of about 120 deg C)
> In a practical dirigible design, the difference is significant, making a 50% difference in the fuel-carrying capacity of the dirigible and hence increasing its range significantly
But I wouldn't know :)
> While helium is exceedingly light as compared with air, it is somewhat heavier than hydrogen. The total lift of a helium-filled dirigible is accordingly some 10% less than that of the hydrogen-filled airship. The difference does not appear important at first sight, but the total lift of the gas carries the structure, the motors and the crew. It is only the last 20% or so that is available for carrying fuel, and hence a difference of 10% in the gross lift may spell a difference of 50% in the fuel-carrying capacity. On long-distance flights this difference is vital.
> Nor is the danger of fire totally eliminated with the use of helium; the gas-tanks and the fuel system generally are still vulnerable. But when a ship is properly designed and carefully handled, the danger of fire is comparatively small, even with hydrogen.
https://web.archive.org/web/20110209024932/http://www.time.c...
No.
Hydrogen is highly explosive/flammable — that is why Helium is preferred.
But that doesn't significantly impact rarity of hydrogen, as it reacts very readily and is typically found in compounds.
You don't find much hydrogen gas in nature (~1ppm in the atmosphere, vs 5ppm for helium).
Better the hydrogen, a few small technical problems aside.
Gravity also matters here.