A collection of photos in posts by Miles Lumbard there is a page titled Mercury Retro Pack Walk Around Page 1 (spotted here in reference to the thermal zebra stripes) can be found nine images with the caption:
Any questions, comments, or problems, please email me.
These pictures were taken and shared with the web by Miles Lumbard .
Photographed at the Smithsonian's National Air and Space Museum in Washington, D.C.
Below are small cropped sections from photos 1 and 3 showing the heat shield, which looks like some kind of translucent organic resin or perhaps phenolic material.
My understanding is that this is some kind of ablative material; when exposed to high temperature during reentry the surface is constantly "gassifying" producing a layer of gas of organic molecules which are opaque to the thermal infrared light radiated by the hot gas and plasma in the reentry shockwave. The gas absorbs the radiated heat and quickly moves off and is replaced by a fresh supply as the shield continues to generate more to replace it.
- What material composition(s) were used in the Mercury Heat shields?
- How were they manufactured in just the right shape, and without internal stresses?
- What are all those concentric ridges seen inside or behind the translucent shield material?