January 31, 2013

Friedlander Cold Crown 2: A Conversation With Goat Guy







A guest post by Joseph Friedlander for Next Big Future



The reader known as Goat Guy is a regular in the talkbacks at Next Big Future, many have been entertained by his opinions, backed up by hard engineering calculations. This is a follow up examination of the Friedlander Cold Crown and managing large scale lunar industry. The purpose of the Friedlander Cold Crown is to capture runaway gas escapes that otherwise would ruin the wonderful Lunar ambient vacuum during a period of massive industrial bootup. For current lunar atmosphere, Landis gives ten million molecules/cubic centimeter (half nanotorr) during the lunar day 100,000 molecules/cubic centimeter during the lunar night, This corresponds to pressures from 0.001 nanotorr This is good enough to use vacuum tubes without the tube, a vacuum technician’s paradise easily spoiled by large scale outgassing. 

I had a correspondence with him about the Friedlander Cold Crown
whose purpose is to capture runaway gas escapes that otherwise would ruin the wonderful Lunar ambient vacuum during a period of massive industrial bootup.


For current lunar atmosphere, Landis gives ten million molecules/cubic centimeter (half nanotorr) during the lunar day 100,000 molecules/cubic centimeter during the lunar night, This corresponds to pressures from 0.001 nanotorr 
 This is good enough to use vacuum tubes without the tube,  a vacuum technician’s paradise easily spoiled by large scale outgassing.



I wrote Goat Guy:

My gut (and I have a considerable gut) tells me the lunar polar Cold Crown http://nextbigfuture.com/2011/12/friedlander-cold-crown-cold-trap-for.html would work but I would love to know a best guess as to what efficiency (possibly as little as 1/1000th of the 'book value' of many teratons of frozen gas a year).  The way I approached the problem was the old movie trope (if Earth is ripped from the Sun how long to freeze the atmosphere) but on a vacuum world like the Moon I don't think it would be so efficient. (3 ways to get rid of heat, conduction, convection, radiation is the least efficient use of surface area of the three)





I am curious as to how you would approach the problem.  I believed the shadowed circles on the Lunar poles with the hardware described would do the job and are big enough once cooled down to freeze oxygen at a single bound (or rebound, but the 50s Superman TV show had an unnatural influence on my childhood :) The random walk of escapee oxygen stray molecules would often lead it back to a second cooling opportunity.  But my guess is one thing, a GoatGuy analysis of the problem another---love to see it.

Goat Guy wrote back:


 (re: Ice King crown) - It is an interesting proposition - but I think you might have forgotten that enthalpy works both ways.  It takes specific and finite energy to dissociate oxygen to a vapor phase, and it releases a specific and rather significant amount of energy on being condensed to liquid/or/solid.  If less-than-88K is needed, remember that all the condensate will be pushing temperatures UP, with only black-body radiation available to cool everything down.

Now, while there are a LOT of seconds in a year (31.5 million of them),  11 tons per square meter per year is still 0.35 grams per sq. meter per second.  
31536000
s (yr)
11000000
g (oxy)
0.35
g/s
6.8
kJ/mol
32
g/mol
0.01
mol/s
74.12
J/s

So... 75 additional watts of heat per square meter.  Feel like doing the Black-Body thing and calculating both backward what "88K" (converted to blackbody watts) + 75 watts ... reconverted back to degrees K is?   I don't think it is close to 88K.

[calculating]

OK, 88 K equals 3.4 watts per square meter. 
190.15K equals 74.12 watts per square meter.

Obviously... too high a temperature to equalize into a workable Friedlander steady-state oxygen trap.  

Indeed ... your budget is actually more like "1 watt per square meter" above and beyond the natural background lunar regolith output.  So... instead of 11 tons/square meter per year, adjust down by 1/75th of that.  Maybe then it'd work.

=GoatGuy=

Taking Goat Guy’s suggestion,  the previous value of 5 teratons (5 million megatons) of oxygen freezeout capabilities  which could capture the oxygen waste from  vigorously processing about a Phobos (Mars’ larger moon) of moon rock per year.

Divide that by 75 or 100 to be sure, and from 10 teratons (10,000 gigatons) of rock vigorously deoxygenated we then are able to process a mere 100 gigatons of rock a year without affecting the Lunar atmospheric ambient.


 Without the Friedlander Cold Crown we would be lucky to deoxygenate
 10 million tons of rock a year before slightly messing with the vacuum because of the limited natural Lunar vacuum purging  mechanisms  detailed in the Landis references in the first article.

So that is 10,000 times as much industry for a lunar bootup with no outgassing problems.

100 billion tons of lunar rock would enable a supply of at least 20-30 billion tons of usable metals.



Here are typical contents of the lunar regolith by main regions:

Chemical composition of the lunar surface regolith (derived from crustal rocks)



Compound        Formula   Composition (wt %)
                Maria Highlands
silica          SiO2       45.4%   45.5%
alumina         Al2O3      14.9%   24.0%
lime            CaO        11.8%   15.9%
iron(II) oxide  FeO    14.1%    5.9%
magnesia        MgO         9.2%    7.5%
titanium dioxide TiO2       3.9%    0.6%
sodium oxide    Na2O        0.6%    0.6%
Total                      99.9%  100.0%
 

Wikipedia on the moon

Note that this is one set of tables on a global average, specific sites could for example double the titanium (and note also these are expressed as oxides, so for example that's not 4% titanium but more like 2%.in the table above.--But in the Sea of Tranquility, for example, you could probably get 4% in random regolith. If you can export from multiple sites, you can often find 10% iron, in a separate place 4% titanium, perhaps 12%+ aluminum, and at another site as much magnesium--using totally different regolith types.)

Keep in mind that by weight oxygen is about 40 % of the lunar regolith and silicon and calcium together around 30 % and you will see that potential export metals are only about a quarter of regolith weight.

30 gigatons a year of exported metals plus potentially another 30-50 gigatons of less valuable mass  (but useful--- lunar fused quartz, ) and we can see that the future Lunar industrial bootup will be on a scale greater than present day Earth industry.  The great lunar resources of  near free power and cheap vacuum (and easy export to near Earth space) will ensure that the Earth-Moon industrial center of gravity will be above Earth’s atmosphere, not below it.

Some other articles on Lunar and Space  Industrial buildup—and what to do with it









http://nextbigfuture.com/2010/03/in-praise-of-large-payloads-for-space.html





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