(urth) Dome, Dome on the Range

[Jerry Friedman]

> From: Jeff Wilson <jwilson at io.com>

> On 1/15/2011 11:51 PM, Jerry Friedman wrote:
> >> 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.
> 
> It can escape the moon moving rearward, going into an  elliptcial orbit,

Those seem like two ways of saying the same thing--headed for Urth, going 
backwards
relative to Lune, which puts it into an elliptical orbit that intersects with 
Urth.
 
> > 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.
> 
> I considered  that last, but the infalling gas regains the kinetic energy 
> so when it  returns it heats the atmosphere, increasing the rate other 
> gas leaves, so  that much more gas is available to take non-returning 
> paths while  maintaining the same overall rate of depletion.

It just puts back the energy it took out with it, partially compensating for the
evaporative cooling.

> Not to 
> mention all  this gas farting around lunar orbit is a hazard to navigation.

Much like Earth's atmosphere.

Jerry Friedman