An interesting feature of the satellite is the synthetic sapphire that was used to cover the solar cells. This robust synthetic sapphire was instrumental in keeping out solar protons and was especially helpful after a nuclear test destroyed other satellites that were launched into orbit near Telstar 1.

Synthetic Sapphire for non-gemstone applications

Synthetic sapphire crystals can be grown in cylindrical crystal ingots of large size, up to many inches in diameter. As well as gemstone applications there are many other uses:

The first ever laser produced was based on the ruby chromium impurity in sapphire. While this laser has few commercial applications, the Ti-sapphire laser is popular due the relatively rare ability to tune the laser wavelength in the red-to-near infrared region of the spectrum. It can also be easily modelocked. In these lasers, a synthetically produced sapphire crystal with chromium or titanium impurities is irradiated with intense light from a special lamp, or another laser, to create the stimulated emission.

Pure sapphire ingots can be sliced into wafers and polished to form transparent crystal slices. Such slices are used as watch faces in high quality watches, as the material's exceptional hardness makes the face almost impossible to scratch.

Wafers of single crystal sapphire are also used in the semiconductor industry as a substrate for the growth of gallium nitride based blue and green light emitting diodes.
http://www.answers.com/topic/sapphire

A crystal can be made from any clear material, from plastic to synthetic sapphire, which is the hardest and most expensive crystal available.
http://www.zales.com/ProductKnowledge.aspx?pid=71#Crystal



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Note added at 1 hr 30 mins (2005-04-25 03:53:52 GMT)
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The high quality synthetic sapphire Rayotek uses in its custom products is, like natural sapphire, single crystal aluminum oxide (Al203). The main advantage that the synthetic form of sapphire has over natural is that it can be \'grown\', either in a boule up to 300mm in diameter or in the form of a tube.

The largest size of a sapphire product cannot exceed the largest boule that can be grown. Therefore, the largest parts made cannot exceed 300mm for two of the dimensions.
http://www.rayotek.com/synthetic_sapphire.html