Why is the Apollo LM landing gear covered with so much thermal insulation?

Question

The Apollo LM landing gear – struts, footpads, shock absorbers and contact probes was completely covered with foils.

There should be no temperature sensistive electronics within the landing gear, only switches and cables for the contact probes.

So what should be protected against extreme temperatures?

Image AS11-40-5915.jpg from Apollo 11 Lunar Surface Journal.

Has it just been my imagination all these years, or are there two slightly different color films? — uhoh, Aug 02 '19 at 10:31
@uhoh I see four different foil types. It may be another question. — Uwe, Aug 02 '19 at 10:45
speculation: without insulation, the legs would act as radiators, cooling down or heating the descent stage. — Hobbes, Aug 02 '19 at 10:51
@Uwe How many different kinds of insulation film are wrapped around the Apollo Lunar Module? — uhoh, Aug 02 '19 at 10:52
@Hobbes I think it's to protect the lunar surface; if it gets too warm the cheese will melt and flow... — uhoh, Aug 02 '19 at 10:53

Uwe · Accepted Answer · 2019-08-05T19:10:04.103

Everything of the Lunar Module should be as light as possible. Therefore no thick-walled, heavyweight, pneudraulic-type struts were used to absorp the landing shock but lightweight aluminum honeycomb cartridges. Shock was absorbed by crushing the honeycomb cartridges.

The footpads were build as a sandwich structure of a honeycomb core between two aluminum panels.

The aluminum honeycombs were assembled using adhesives, also the footpads. The used aerospace aluminum alloys and the adhesives should not be too hot or too cold, they would loose their strength otherwise.

Landing-gear thermal insulation must maintain the landing-gear temperatures at or below design levels to ensure positive structural margins of safety and proper mechanical operation during deployment and landing. Furthermore, temperature control of the honeycomb energy absorbers within specified limits is necessary to preclude large variations in crush-load levels.

From: APOLLO LUNAR MODULE LANDING GEAR pdf

According to this pdf, long term temperature of most honeycombs should be lower than 350 °F or about 175 °C.

About 300 °F or 149 °C may reduce strength to about 80 %.

I notice the quoted text refers to "positive structural margins of safety and proper mechanical operation", which I take to include both structural failure to due to either excessively high or low temperature, but also mechanical issues such as binding of the moving parts due to differential expansion/contraction. — Anthony X, Aug 06 '19 at 00:12

Why is the Apollo LM landing gear covered with so much thermal insulation?

1 Answers1

Linked