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|PRODUCT DATA of 09: Optical Materials|
|Material||09: Optical Materials|
|General Information||The classical meaning of the word "glass" is extended in this Standard to cover "organic glass" and some crystalline optical materials.|
|Use in Spacecraft||Glasses, inorganic as well as organic, appear as optical elements: e.g. windows, lenses, prisms, solar-cell covers and filters.|
|Main Categories||Optical materials can be grouped as:
|Processing and Assembly||Inorganic glass parts are mainly assembled by means of flanges and gaskets or adhesives. Glass-to-metal welds are possible. Assembly shall be rigid enough to provide accurate alignment but shall also be designed to cope with thermal expansion and provide suitable damping.
Organic glasses are easily machined: this operation can be performed on inorganic glasses by using special techniques (e.g. ultrasonic machining).
|Precautions||Glasses are transparent only to a certain wavelength range and shall be chosen in accordance with the mission requirements. Inorganic glasses are sensitive to mechanical and thermal shocks. Organic glasses are easily scratched and lose their polish.
Assembly methods are the most important points in the design of parts containing glass and particular attention shall be given to matching the thermal expansion coefficient of the optical material with that of its mounting.
|Hazardous and Precluded||Canada Balsam and other similar products shall not be used in the assembly, since they are liable to produce contaminants.
Organic glasses should not appear in high-precision equipment except as plain windows or light-pipes.
|Effects of Space environment|
|Some Representative Products||In the case of inorganic glasses pure silica should be used. This is sold by many European firms under many different trade names, for example:
Optical glasses are mainly designated by reference numbers from manufacturers like SCHOTT (D), CORNING (USA) and PILKINGTON (UK).
For solar-cell covers, the main sources are still OCLI (USA) and PILKINGTON (UK). Some are manufactured with an electrically conductive surface such as ITO by the same manufacturers.
Optical solar reflectors (OSR) based on silica/silver/inconel or silica/aluminium are manufactured by OCLI. PILKINGTON produces OSR’s based on cerium glass/silver-nickel-chrome.
Filters aremade by BALZERS(CH), SCHOTT(D),ASTRIUMSAS(F),M.T.O. (F), BARR and STROUD (UK) and THALES (UK).
Organic glasses based on acrylic and methacrylic polymers are well known: PLEXIGLAS from ROHM and HAAS (D), PERSPEX from ICI (UK). Polycarbonates like MAKROLON (BAYER, D) can also be considered as well as several polystyrene grades.