Any help would be welcome.from NASA's Mar's Rovers site (second link).
An ablative heat shield is a type of protective material that is used to shield spacecraft and other objects from the intense heat and pressure experienced during atmospheric entry. It is designed to gradually burn away and dissipate the heat, rather than reflecting or absorbing it.
The most commonly used materials for ablative heat shields are carbon-based composites, such as phenolic resins, reinforced with materials like fiberglass or silica. Other materials that have been used include cork, balsa wood, and various ceramics.
As the spacecraft enters the atmosphere, the heat shield is exposed to high temperatures and begins to char and burn away. This process releases gases, which create a boundary layer of cooler gas between the shield and the hot gases outside. This insulating layer helps to protect the spacecraft from the extreme heat.
One of the main benefits of using an ablative heat shield is its ability to effectively dissipate heat and protect the spacecraft from high temperatures. It also allows for a lighter weight design, which is crucial for space missions. Ablative heat shields are also relatively easy to manufacture and can be tailored to specific mission requirements.
Ablative heat shields are primarily used for spacecraft and space capsules, such as the Apollo and Soyuz capsules. They are also used for re-entry vehicles, such as the Space Shuttle, and for ballistic missiles. In addition, ablative heat shields have been used for other applications, such as protecting rocket engines and industrial equipment from high temperatures.