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Author
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Topic: Why did the Apollo LM have four legs?
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Steve DeGaetano
Member Posts: 19
From: Wake Forest, NC , USA
Registered: Sep 2010
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posted 07-16-2019 09:34 AM
   
Why did the Apollo lunar module have four legs? Wouldn't three have made more sense, because all three legs would make contact with the ground in any scenario? |
Headshot
Member Posts: 891
From: Vancouver, WA, USA
Registered: Feb 2012
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posted 07-16-2019 09:56 AM
Designers were concerned that the lunar surface was covered with soft powder and the LM might sink to unknown depths. This was the scenario presented by noted Cornell scientist T. Gold. So the LM had four legs (one design configuration had five legs) and large landing pads to distribute the load across the lunar surface. In 1966, when the soft-landing Surveyor spacecraft found this situation was not so, it was way too late to change the design of the LM. |
Ross Sackett
Member Posts: 18
From: Santa Fe, NM
Registered: Aug 2015
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posted 07-16-2019 10:23 AM
Three legs only work well if they were landing on a flat and level surface. Designers had to deal with pad-in-a-hole and pad-on-a-rock scenarios that might have toppled a top-heavy three-legged LM. Grumman explored several options, and initially came up with a 5-pad design that maintained the needed "support triangle" even when one pad was far out of plane with the others. As they learned more about the lunar surface (mainly from Surveyor) it became clear that four pads on compliant legs would be plenty. |
Jim Behling
Member Posts: 1488
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 07-16-2019 10:57 AM
The LEM had five legs and the LM had four legs. Four legs worked with the box/hashtag structure of the descent stage. |
SpaceAholic
Member Posts: 4494
From: Sierra Vista, Arizona
Registered: Nov 1999
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posted 07-16-2019 05:31 PM
quote:
Originally posted by Jim Behling:
The LEM had five legs and the LM had four legs.
The design change from five to four legs occurred in 1963: LEM was used as a term of reference through 1967.
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oly
Member Posts: 971
From: Perth, Western Australia
Registered: Apr 2015
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posted 07-16-2019 09:20 PM
quote:
Originally posted by Steve DeGaetano:
Why did the Apollo lunar module have four legs?
The four leg design came about after the shape of the decent stage was changed from a circular to a cruciform. The original concept design of five legs was found to be the lightest option, however, four leg design better suited the design change.Details can be found within this document, page four "Development History." |
Jim Behling
Member Posts: 1488
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 07-17-2019 08:44 AM
quote:
Originally posted by SpaceAholic:
LEM was used as a term of reference through 1967.
It was officially changed in April of 1966. Official documentation since then reflects that. |
Steve DeGaetano
Member Posts: 19
From: Wake Forest, NC , USA
Registered: Sep 2010
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posted 07-17-2019 05:34 PM
Thanks everyone. |
Blackarrow
Member Posts: 3160
From: Belfast, United Kingdom
Registered: Feb 2002
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posted 07-17-2019 06:06 PM
As in George Orwell's "Animal Farm," so too in lunar module planning: "Four legs good, two legs bad." |
oly
Member Posts: 971
From: Perth, Western Australia
Registered: Apr 2015
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posted 07-20-2019 07:45 AM
quote:
Originally posted by Jim Behling:
It was officially changed in April of 1966.
While it was officially changed from LEM to LM, many still called it by the original term, including Armstrong. "I'm going to step off the LEM now." |
Robert Pearlman
Editor Posts: 43576
From: Houston, TX
Registered: Nov 1999
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posted 07-20-2019 08:15 AM
Since LM and LEM are pronounced the same, how do you know what spelling Armstrong was using? |
Jonnyed
Member Posts: 408
From: Dumfries, VA, USA
Registered: Aug 2014
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posted 07-20-2019 10:47 PM
For what it is worth, last night's National Air and Space Museum Apollo Go For the Moon: 50th Anniversary show on the Washington Monument/National Mall had the acronym "LM" in the closed caption (not surprising) when playing the recording of Neil's report from the ladder of the LM.(By the way, what an awesome show — glad I got to see it in person from a fantastic location.) |
oly
Member Posts: 971
From: Perth, Western Australia
Registered: Apr 2015
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posted 07-21-2019 06:25 AM
quote:
Originally posted by Robert Pearlman:
Since LM and LEM are pronounced the same, how do you know what spelling Armstrong was using?
With the earlier designation of Lunar Excursion Module abbreviated to the acronym LEM, it became common for people associated with the machine to use the pronunciation "LEM." This identity can be traced through the Lunar Module documentation history, including through the post name change to LM era. If for argument sake, the original designation had been LM, it seems highly unlikely that the vehicle would become known as the "EL-EM." It could just as easily become known as the Bug, The Cement Mixer, or the Spider. This follows since the Command and Service Module was called "C-S-M," rather than "ceessmem." The reason that the lunar module became known as the LEM is that it was originally designated lunar excursion module. There is documented record stating that the term "LEM" was a carryover pronunciation, with many individuals stating that, to them, the machine would always be the "LEM" and that continuing the trend made training and discussion easier. I do not believe that Armstrong was using either spelling while speaking, because I doubt he was writing anything down at the time. I do believe that he was using the traditional term "LEM" because he had been associated with the program for so many years, and it was commonplace within the program. NASA love acronyms, and probably spend many hours researching, refining, and approving such names. It is probably a good thing that the Apollo Lunar Surface Experiments Package was not called the Apollo Research Science Experiment. |
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