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Is a layer of He and Hydrogen at the edge of our Atmosphere?

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Serigia
1389631.  Sun Sep 12, 2021 4:26 pm Reply with quote

From what I've read the last ten minutes it sounds like lighter than air elements escape similar to how water evaporates, so molecules are constantly accumulating the energy needed to escape but there must be a reservoir of the stuff up there for it to escape from.
Similar to the space elevator idea where you build a tower at the equator couldn't we stick a pipe up and suck it back down. I'd imagine it would gather at the equator as that's the fastest rotating point if that influences the atmosphere at all. I call this idea the Skyscraper and perhaps it could be a way to reclaim some of our gas emissions as an added bonus.

 
PDR
1389636.  Sun Sep 12, 2021 6:14 pm Reply with quote

The hydrogen escapes into space because the RMS velocity of the hydrogen molecule [kinetic theory of gases: (3RT/M)^0.5 and all that jazz] is greater than the escape velocity at the edge of the atmosphere. So only the enormous gravities of very large (massive) planets like Jupiter, Neptune, Saturn & Uranus can actually keep hydrogen captured. That's why there is essentially no naturally-occurring hydrogen on earth. I'm hazy on gas laws these days - the details could be better better explained by a physicist like DrBob.

Also space elevators are a flawed concept because they would need too much structural bracing to react the forces resulting from the way they violate the conservation f angular inertia. Even ignoring that aspect, they would be structures whose centre of mass would need to be 22,000 miles from the bottom of the tower. Even texans would see that as a tad on the large side.

PDR

 
Numerophile
1389645.  Mon Sep 13, 2021 3:15 am Reply with quote

PDR wrote:
Even ignoring that aspect, they would be structures whose centre of mass would need to be 22,000 miles from the bottom of the tower.

The atmosphere is only about 300 miles thick, and 99.99997% of its mass lies below 62 miles (the Kármán Line). The International Space Station orbits at a mean altitude of 230 miles.

So I think your arithmetic may be a little awry...

 
PDR
1389647.  Mon Sep 13, 2021 3:39 am Reply with quote

No - the "space elevator" concept involves the centre of mass of the tower being geo-stationary (hence the 22,000 mile bit).

PDR

 
Numerophile
1389660.  Mon Sep 13, 2021 6:55 am Reply with quote

Fair enough.

I was thinking in terms of sucking hydrogen back to earth from the edge of the atmosphere, as originally suggested. (I take the point that since it doesn't actually accumulate there, the whole idea is a non-starter.)

 
PDR
1389857.  Tue Sep 14, 2021 5:09 pm Reply with quote

Numerophile wrote:
Fair enough.

I was thinking in terms of sucking hydrogen back to earth from the edge of the atmosphere, as originally suggested. (I take the point that since it doesn't actually accumulate there, the whole idea is a non-starter.)


Ah, see what you were getting at. It's the "space elevator" tag which "popular science" feels is an easy solution to getting stuff into orbit using energy rather than impulse, when actually there a number of fundamental issues:

1. It can only get stuff to a geo-stationary orbit, and that's a rather high orbit which has limited uses.

2. It also means the structure must (as previously mentioned) be huge. We currently can't built a one mile high building, so a structure well over 20,000 miles high (to put its centre of mass at the geostationary orbit) isn't exactly an easy, risk-free project.

3. The issues associated with conservation of angular inertia (or Coriolis compensation if you prefer) when mass is moved up or down the elevator would introduce orbital lead/lag forces that would stress the tower, and could introduce hormonic problems (any structure that slender must flex, and so will have lots of natural frequency modes)

4. It would be subject to day/night and seasonal heat cycles that would vary its length, causing the centre of mass to move above/below the geostationary orbit with a consequent tangental oscillation. This could be synthetically compensated (or damped), but that introduces further large machinery with some nasty failure modes.

5. It is currently economically impossible to build a building much higher than about 3,000 feet because the interest on the construction debt makes the debt grow to a runaway value (ie where the maximum possible revenue won't even cover the interest on the debt, let alone payback the capital) before the building can earn revenue to service it, so building that large a structure can't be an economic reality.

6. etc

PDR

 
tetsabb
1389880.  Wed Sep 15, 2021 4:56 am Reply with quote

PDR wrote
Quote:
hormonic


Splendid typo, dear boy!

 
PDR
1389893.  Wed Sep 15, 2021 5:50 am Reply with quote

A common typo at this time of the month...

PDR

 

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