Turns out -- no, it permanently escapes to space with the help of the solar wind
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The overall amount of helium in the atmosphere is still more than enough for the foreseeable future, and it could be extracted (albeit at high energy cost) by augmenting existing air separation units (ASU's). Of course natural gas wells currently provide an easier to extract source, seeing as the concentration there is way higher.
Helium is only 5ppm in the atmosphere. Extracting useful quantities of it that way will probably never be economically viable. In other words, if for some reason we can no longer get helium from natural gas wells then it will be cheaper to just let patients die instead of doing cryogenic distillation of helium from the atmosphere to run MRI machines.
MRI could switch to LH2. Yes, it's explosive and higher boiling temperature so would not support as high field and incompatible with currently used semiconductors. But it's doable. Plenty of other important uses (i. e. semiconductors and lasers) where it is much more irreplaceable.
New MRI only use 7 Liters (25 Cups) instead of ~1500L (~330Gallons) of liquid Helium due to better sealed magnets.
https://mriquestions.com/uploads/3/4/5/7/34572113/philips_bl...
In a world of extremely cheap solar electricity pushing grid prices negative, a lot of things might be a lot more economical then conventionally thought though - particularly when you factor in the desire to get a full return on industrial manufacturing of panels.
For me personally, this is one of the most promising aspects of solar that I hope to see in the future. There are many, many things we could do but currently do not because the energy cost is not worth it. Push the energy cost to zero, or even below, and it will be interesting to see what new things become abundant.
CO2 capture from the atmosphere, turning it into hydrocarbons. All the solar panels/wind farms combined have quite large surface that might be useful for the capture. Just need to figure out the mechanism to do it. Easy-peasy, right? :-)
We are already separating out the majority elements from air via ASU plants, so we should compare the abundance of helium in what is left from typical extraction. And that looks quite technically viable, if obviously uneconomic at present.
This is a very good point.
Oxygen, nitrogen, CO2 and argon make up 99.94% of the atmosphere. The remaining 0.06% has 5ppm is nearly 1% helium. That's up 200x from the original concentration and is well above the 0.3% that is sometimes quoted as the limit for economic extraction of helium (and well below the 7% of some natural gas).
Furthermore, the leftover gas is also already cold. It is absolutely true that 85K isn't very close to the boiling point of helium, it is a lot closer than starting at the temperature of gas at the well head.
The gotcha is almost certainly going to be that an ASU probably doesn't liquify most of the gas it takes in. That means that the exhaust gas will only be slightly enhanced.
http://wordpress.mrreid.org/wp-content/uploads/2014/06/atmos...
the density is low though
observe that where Helium becomes a significant percentage, there is also Hydrogen and (monoatomic) Oxygen.
if one were driven by purism or vanity for stoichiometric exactness, then at a height of 1000 km theres 2 Hydrogens per Oxygen atom, so this could be reacted to water, and the energy used to power compression of the Helium, the water would freeze.
without this vanity, helium becomes a significant fraction at much lower heights... and thus higher densities.
The energy to compress becomes nearly insignificant at low pressures.
if humanity ever builds space elevators, this will be one of many benefits of having space elevators.
Space is at the top of the atmosphere right? That place is full of stars producing helium by the teragram.
GP ain't wrong, but the phrasing implied we'd have it closer by than it actually is.
No, they're entirely incorrect because they used the word "near". There is no practically usable helium near the top of the atmosphere.
But, I'm also confident they were making a silly joke.
Is this graph wrong?
http://wordpress.mrreid.org/wp-content/uploads/2014/06/atmos...
I'd believe it. Wikipedia has a similar one [1] but it shows a bit more hydrogen than helium at higher elevation.
Awesome graph! Worth stating that the increase in the relative fraction of He isn't so much because there's a lot of He out there as because there's a lot less of everything else. Overall density falls off roughly exponentially but lighter elements have a longer tail.
So once you get out to a few earth radii quite a bit of what you see might be ionized helium but that doesn't mean you can do much with it.
[1]: https://en.wikipedia.org/wiki/File:Chemical_composition_of_a...
> There is no practically usable helium near the top of the atmosphere.
The context of this discussion and the fourth word in that sentence is important. Something existing isn't the same as something being practically available. That graph isn't wrong, percentage wise, but it's missing both density an cost per liter that makes it relevant to this discussion.
The practicality is a function of many things:
the amount of people simply considering extraction of such helium
the amount of research into comparing hypothetical methods of extraction
the level of technology of a civilization
Agreed, but there's a reasonable bounds for that future context that sets what's "practical", at the time these reserves would run out if not replaced (this discussion), with that context partially dictated by todays practical alternatives (which also happen to be the exact same as the original source of the reserves!).
For an idea of the difficultly, compared to not bleeding helium into the atmosphere (as the petrol companies do now): the atmospheric pressure at those elevations is around 1/10,000,000,000,000 of that at sea level. To fill one party balloon, you would need to capture something like 5,000,000,000,000 party balloons of that atmosphere. Note: math might be a relatively negligible couple orders of magnitude off.
Even if it didn't, collecting it seems wildly expensive.
Or free if we managed to run solar powered sails (or so) skirting the very top and autonomously sending the harvest down.
If by “free” you mean “very very expensive” then i agree with you. It would cost a fortune to even just attempt a pilot project proving feasability. Then we would need to send up regular replacements to the “sending the harvest down” hardware at the minimum. Just imagining the cost of a tank which can be launched into space, autonomously dock with the collector sails, then deorbit and land makes my head spin. And then doing that at scale, paying people to launch it, paying people to operate the system.
It could be free if we imagine some crazy advances in autonomous self-replicating spacecrafts. But by then we live in the post-scarcity diamond age probably.
I meant some semi permanent harvesters (which would cost a fortune to build and deploy).
Sending the harvest down could maybe happen inside plastic containers built in place, made with the abundant sunlight, some Co2 and water (not sure if there's CO2 this high though. In retrospect we'd need also some metals to print some sort of the antenna reflecting radar frequencies (for the ground stations tracking them on the approach)?
And with the hundreds of small containers (carefully balanced so they don't smash in the ground but slowly rain onto the area) maybe it'd be easier.
I don't know. I think it's hard sci-fi, achievable within our lifetimes :)