Why Did the Apollo LEMs Have a Four Leg Landing Gear?

[Glenn]

Why did the Apollo LEMs have a four leg landing gear instead of a three leg landing gear?

I saw some old photos of LEM concepts using a three gear setup and it got me wondering why they went to a heavier 4 gear setup.

Thanks,
Glenn

 

[FredGarvin]

I found this just snooping around:

"Apollo LEM landing gear design freeze:

MSC Director Robert R. Gilruth reported to the MSF Management Council that the LEM landing gear design freeze was now scheduled for August 31. Grumman had originally proposed a LEM configuration with five fixed legs, but LEM changes had made this concept impractical. The weight and overall height of the LEM had increased, the center of gravity had been moved upward, the LEM stability analysis had expanded to cover a wider range of landing conditions, the cruciform descent stage had been selected, and the interpretation of the lunar model had been revised. These changes necessitated a larger gear diameter than at first proposed. This, in turn, required deployable rather than fixed legs so the larger gear could be stored in the Saturn V adapter. MSC had therefore adopted a four-legged deployable gear, which was lighter and more reliable than the five-legged configuration."

This is from a site that appears to have a pretty good chronology of the design process:

http://www.astronautix.com/craft/lmlggear.htm

Hope this helps.

 

[ravenprp]

The decision to use a four leg landing gear on the Apollo Lunar Module (LEM) was based on several factors including safety, stability, and weight distribution.

Firstly, the LEM had to be able to safely land on the uneven and rocky surface of the moon. The four leg landing gear provided a wider base for stability and better weight distribution, reducing the risk of tipping over during landing. This was especially important since the LEM was designed to land in a vertical position, unlike the horizontal landing of previous spacecraft.

Additionally, the LEM had to be able to withstand the rough terrain of the moon's surface. The four leg landing gear was designed with shock absorbers to help cushion the impact of landing and prevent damage to the spacecraft. This was particularly important since the moon's surface was largely unknown and could potentially have hidden hazards.

Furthermore, the four leg landing gear allowed for a more balanced weight distribution during landing. This was crucial in order to maintain control and stability during the descent and touchdown on the moon's surface. The three leg landing gear, while lighter, would have placed too much weight on one side of the LEM, making it more difficult to control and potentially increasing the risk of tipping over.

Lastly, the four leg landing gear also provided a backup in case one of the legs failed to deploy or was damaged during landing. The LEM's design prioritized redundancy and safety, and having four legs instead of three provided an extra level of security in case of any unforeseen issues.

In conclusion, the decision to use a four leg landing gear on the Apollo LEM was a carefully considered choice that prioritized safety, stability, weight distribution, and redundancy. It proved to be a successful design that allowed the LEM to safely land on the moon's surface and fulfill its mission.