Re: Monday answer
Gary Smyth
No gold star today.
The answer is heat shield tiles for space re-entry vehicle. I was going originally to identify the oak as white oak but I thought that that would be too easy to link with military/China/white oak.
The Chinese Space Agency (which is military managed) has developed the most elegant and amazingly cheap method of building a re-entry shield for their single-use re-entry vehicles. They use white oak wood. A thick piece of oak is an ideal insulator and ablative material. Oak burns very slowly and it does not transfer heat very readily. Chinese scientists reasoned that since white oak buildings are very difficult to burn down, why not check it out. Anyone who has ever tried to burn oak logs on a fire will confirm this. A big, hot fire is needed to ignite oak, and it will burn slowly for hours.
So, the message here is that modern, hi-tech solutions are not necessarily the answer to the problems of living in space. Simple, cheap and well-tried solutions may serve just as well in some cases, even with respect to highly technical problems
Ablation cooling or simple ablation is a process in which heat energy is absorbed by a material (the heat shield) through melting, vaporization and thermal decomposition and then dissipated as the material vaporizes or erodes. In addition, high surface temperatures are reached and heat is dissipated by surface radiation, pyrolysis of the surface material causing formation of a "char," and the generation of chemical by-products which move through the char carrying heat outward towards the surface boundary. The rejected chemical by-products then tend to concentrate in the ablation boundary layer where they further block convective heating. These ablative materials may be chemically constructed or made from natural materials.
�An ablative material known as polydimethylsiloxane has been used in the U.S. on manned reentry capsules in the past. An elastomeric silicon ablative material was used in the Discoverer program. An example of a natural material is the oak wood heat shield used on the Chinese FSW reentry vehicles.� (Looking up �China, FSW vehicles, will support the answer) also (http://www.fas.org/nuke/intro/missile/basics.htm)
