Behavior of Materials in Space Environments

The quantitative effects of the environments encountered in various regions of space upon several kinds of engineering materials are discussed. In the vacuum of space, magnesium sublimes appreciably at elevated service temperatures; zinc and cadmium sublime at ordinary temperatures. Most other engineering metals will be unaffected by vacuum except for a slight surface roughening. Among the organics, polysulfides, cellulosics, acrylics, polyvinyl chloride, neoprene, and some nylons, polyesters, epoxys, polyurethanes, and alkyds break down at rather low temperatures in vacuum. Polyethylene, polypropylene, most fluorocarbons, and silicone resins do not decompose significantly in vacuum below 250 deg C. Except for plasticized materials, significant loss of engineering properties in vacuum is unlikely without appreciable accompanying sublimation or decomposition. Also, escape of gases through walls which are gas-tight at l atmosphere will not be of concern. For parts intended to move in contact eith each other in vacuum, lubrication is a serious problem. Certain low vapor pressure oils and greases, tetrafluoroethylene, and thin films of MoS/sub 2/, Au, and Ag can probably provide adequate lubrication when suitably selected for the speeds, loads, and times of service. The particles of the Earth's radiation belts will cause radiation damage to organics and to optical properties ofmore » inorganic insulators. Semiconductors will be damaged in the inner belt; their more sensitive properties will also be affected by solar flare emissions. Exposed surfaces of most materials may be damaged by the radiation belts and perhaps by solar charged particle emissions. Optical properties of exposed polymers and ceramics will also be affected by solar ultraviolet and x rays. Sputtering away of material by collision with ions or atoms in space is probably negligible. Erosion by meteoroids is significant only close to the Earth. The probability of penetration by meteoroids falls sharply with increasing distance from Earth. Much more frequent than penetration is spalling of fragments from the inside of walls struck by meteoroids. The efficiency of walls in preventing penetration and spalling can be increased by splitting the walls into a thin front plate and a thicker main plate; quantitative bases for the design of such spaced armor are presented. (auth)« less