Hot-Spot Plastic

The nose-cone problem--how to bring a missile's warhead down through the atmosphere without too much heat damage--can be approached in very complicated or in very simple ways. A simple way that looks promising for even the fastest-falling missiles: sheathe the cone with Astrolite, a plastic made by H. I. Thompson Fiber Glass Co. of Los Angeles. Astrolite looks like the familiar brownish material used in workers' hard hats, but the fibers that reinforce the plastic are silica (quartz) instead of glass.

When Astrolite is exposed to a blast of high-temperature gas, a thin layer of the plastic on the surface burns off, leaving a mat of silica fibers arranged so that they cannot be easily blown away. At 3,000DEG F. (about the melting point of iron), they begin to soften, but melted silica is sticky, viscous stuff that clings tight until it turns to vapor. The vaporizing process draws heat from the remaining Astrolite and tends to keep it cool.

Astrolite cannot resist continuous high temperature (the plastic binder melts at about 450DEG F.), but it is remarkably successful against short attacks of extreme heat. It is used in 20 types of missiles, sometimes in the nose cones, sometimes in other hot spots such as the nozzles of rocket motors. The Thompson company says that a laminated layer of Astro-lite two-tenths of an inch thick can protect the nose of an IRBM. For an ICBM, which enters the atmosphere much faster, four inches may be needed. This thickness weighs, says Thompson, only one-fifteenth as much as a heat-resistant metal used for the same job.

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