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  Apollo LM crew cabin: pressure vessel skin

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Author Topic:   Apollo LM crew cabin: pressure vessel skin
Apolloman
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Posts: 99
From: Ledignan, Gard (30), France
Registered: Mar 2009

posted 09-30-2012 02:20 AM     Click Here to See the Profile for Apolloman   Click Here to Email Apolloman     Edit/Delete Message   Reply w/Quote
I would like to know the thickness of the skin of the pressurized cabin of the Apollo lunar module.
  • the thickness of the floor where the astronauts were in flight position (before their dashboard);
  • the thickness of the side walls
Incidentally, anyone have pictures of the cabin crew during production of the inside (bare walls without console or equipment)?

nasamad
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Posts: 1949
From: Essex, UK
Registered: Jul 2001

posted 09-30-2012 11:56 AM     Click Here to See the Profile for nasamad   Click Here to Email nasamad     Edit/Delete Message   Reply w/Quote
I don't know the floor and wall thicknesses, only the old story about being able to push a pencil thru them

However, this resurrection of Frank Pullo's old site has some nice images of stage construction.

YankeeClipper
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From: Dublin, Ireland
Registered: Mar 2011

posted 09-30-2012 02:46 PM     Click Here to See the Profile for YankeeClipper   Click Here to Email YankeeClipper     Edit/Delete Message   Reply w/Quote
Apologies that this reply is mostly anecdotal in nature - perhaps someone else can provide exact technical dimensions/specifications.

On my first visit to the Smithsonian in Washington in 1993, I was shocked at how thin the walls of the LM on display there at the time actually were. It's one of my abiding memories of that visit.

In 2011, at Spacefest III, I had an opportunity to discuss my recollection with Apollo 12 LMP Alan Bean. I specifically asked him if the LM walls were really as thin in places as 3 sheets of aluminium foil as I recalled. Alan replied, "3 sheets ? ... more like 1 sheet thick!". He reminded me that the LM was only pressurised to 5 psi, as opposed to the standard earth sea-level atmospheric pressure of 14.7 psi. He also said that you just had to be careful of your movements inside the LM.

Robert Pearlman
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From: Houston, TX
Registered: Nov 1999

posted 09-30-2012 03:11 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
According to page 195 of Scott Sullivan's Virtual LM:
The single wall concept consisted of 1/8" aluminum or equivalent mass.

GACspaceguy
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Posts: 1655
From: Guyton, GA
Registered: Jan 2006

posted 09-30-2012 03:47 PM     Click Here to See the Profile for GACspaceguy   Click Here to Email GACspaceguy     Edit/Delete Message   Reply w/Quote
I was looking at that page as well and thought Wow, 0.125 thick aluminum is huge. The skin of a Gulfstream varies between 0.040 and 0.050 depending on what kind of loading is going on in that paticular panel. The pressure differential at 45,000 feet is about 9 psi for a Gulfstream and the LM was 5 psi. Using that as a guide 0.125 is a staggering large number (like something on the wing skin that see a very large load).

OK, looking at that again I saw where the cross section on that same page has the outer skin at 0.012 minimum which would make sence for 5 psi and add credibility to the oh-so-thin skin stories.

I believe the 1/8 reference may be the single skin thickness equivalent for the multi layer cross section shown on the same page.

Also, the Apollo News Reference for the LM states that the skin is chem milled such that it would be thicker at the structural attach areas and chem milled thinner in the areas that would be required to hold only pressure loads (and not things such as walking loads on the floor for example).

space1
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From: Danville, Ohio, USA
Registered: Dec 2002

posted 09-30-2012 06:15 PM     Click Here to See the Profile for space1   Click Here to Email space1     Edit/Delete Message   Reply w/Quote
In a similar discussion here, I mentioned that the pressurized cabin web thickness was specified as thin as "0.015 to 0.025" inches thick. About every 3-4 inches the thickness increased to "0.055 to 0.065" inches, centered on ribs of 0.812 inches depth, 0.04 inches wide.

The cabin floor was 2" thick honeycomb.

------------------
John Fongheiser
Historic Space Systems

YankeeClipper
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From: Dublin, Ireland
Registered: Mar 2011

posted 09-30-2012 06:46 PM     Click Here to See the Profile for YankeeClipper   Click Here to Email YankeeClipper     Edit/Delete Message   Reply w/Quote
As a follow-up to my earlier post, a BBC Article A3770192 stated this on the subject of the chem-milled aluminum alloy skin:
Crew Compartment

The crew compartment was cylindrical in section in a welded and riveted construction, 92 inches in diameter and 42 inches deep, giving a habitable volume of 160 cubic feet, just sufficient for the two crewmembers to stand side by side. Due to the weight saving programs the compartment skin was reduced to a thickness of 0.012 inches, the equivalent of approximately three layers of kitchen foil.

Here's an Apollo News Reference article on LM Manufacturing which has images of the construction.

Apolloman
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Posts: 99
From: Ledignan, Gard (30), France
Registered: Mar 2009

posted 10-01-2012 10:20 AM     Click Here to See the Profile for Apolloman   Click Here to Email Apolloman     Edit/Delete Message   Reply w/Quote
Thank you all for your answers, but nobody has a picture of the inside of the cabin naked?

Apolloman
Member

Posts: 99
From: Ledignan, Gard (30), France
Registered: Mar 2009

posted 10-01-2012 01:26 PM     Click Here to See the Profile for Apolloman   Click Here to Email Apolloman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by space1:
I mentioned that the pressurized cabin web thickness was specified as thin as "0.015 to 0.025" inches thick.
I might know where you stand this information? I have some PDF on LM but none mentions the thickness!

space1
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From: Danville, Ohio, USA
Registered: Dec 2002

posted 10-02-2012 04:42 AM     Click Here to See the Profile for space1   Click Here to Email space1     Edit/Delete Message   Reply w/Quote
My information is from Grumman LM engineering drawings that I use in the course of my business building museum exhibits.

YankeeClipper
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Posts: 319
From: Dublin, Ireland
Registered: Mar 2011

posted 10-03-2012 06:46 AM     Click Here to See the Profile for YankeeClipper   Click Here to Email YankeeClipper     Edit/Delete Message   Reply w/Quote
As a further follow-up, I wanted to verify a few dimensions and get a true sense of perspective on how thin 0.012-0.015 inches really is.

According to this ALCOA source, US aluminum beverage can walls were approximately 0.015 inches thick in the 1970s. According to this excellent Scientific American article from September 1994, The Aluminum Beverage Can, can wall thicknesses were reduced even further to 0.003-0.006 inches. This study shows that US aluminum soda cans with walls 0.005 inches thin can contain internal gas/liquid pressure loads of 50+ psi.

Moving away from aluminum pressure vessels, I wanted to check relevant dimensions of aluminum sheet and foil. According to this Aluminum Industry document, aluminum sheet is a product 0.008-0.249 inches thick (previously 0.006-0.249 inches), and aluminum foil is a product 0.0079 inches or less thick (previously less than 0.006 inches). Reynolds Wrap Aluminum Kitchen Foil varies in thickness from 0.00064-0.00137 inches as you progress from the standard product to the extra heavy product. So while the aluminum skin of the Apollo LM crew cabin may have been, in certain areas, the equivalent of 3 (very thick) layers of aluminum foil, that foil was not thin modern-day kitchen foil grade. Perhaps kitchen foil of the 1960s-1970s was an awful lot thicker!

Overall, the chem-milled aluminum skin was sufficiently robust for the lunar landing missions. While you may not have been able to push your finger through the side walls, a sharp pointed object or a stray foot may have resulted in disaster so care was needed. Andrew Chaikin wrote in A Man On The Moon (p156):

"In the ascent stage, the walls of the crew cabin were thinned down until they were nothing more than a taut aluminum balloon, in some places only five-thousandths of an inch thick. Once, a workman accidentally dropped a screwdriver inside the cabin and it went through the floor."

YankeeClipper
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Posts: 319
From: Dublin, Ireland
Registered: Mar 2011

posted 10-03-2012 02:45 PM     Click Here to See the Profile for YankeeClipper   Click Here to Email YankeeClipper     Edit/Delete Message   Reply w/Quote
Here are a couple of photos showing some of the interior at an early phase of construction: LM Image 1 | LM Image 2

Hope that might help.

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