(urth) Dome, Dome on the Range

[Jerry Friedman]

> From: Gerry Quinn <gerryq at indigo.ie>

> From: "Jeff Wilson" <jwilson at io.com>
> 
> > It occured  to me at lunch today that a problem with the open air atmosphere 
>schemes, even  ones that last thousands of years between refills, is that they 
>take half to 3/4  the mass of earth's atmosphere to work. When this does escape 
>from the moon,  only small amount of that will also escape from the earth, and  
>the reset  will eventually come to fall on the earth, raising its surface air 
>pressure  accordingly; this is a serious problem
...

> Seriously, will this actually happen, anyway?  I couldn't find  detailed 
>references to a proper calculation, but here are my thoughts:
> 
> If  an atom leaves the top of Lune's atmosphere at lunar escape velocity, the  
>question of whether it is likely to end up in Urth's atmosphere on Urth depends  
>on whether it exceeds Urth escape velocity at this point (unless it's headed  
>directly for Urth, which is unlikely.

[snip calculation]

I like it, but you need to add in the orbital velocity of Lune, which makes 
molecules substantially more likely to escape.  (This could actually be a bigger 
problem than air ending up back on Urth, where as you note it's not lost.)

Also, molecules that escape from Lune but not the Lune-Urth system will be in 
orbits that intersect Lune's orbit where they left it. Except for the relatively 
small portion aimed at Urth, they're not going to come to rest on Urth until 
their orbits are modified by collisions with other molecules or brushes with 
Lune.  I suspect they're a good deal more likely to come to rest back on Lune 
than on Urth.

Jerry Friedman