Abstract
The effects of spatial environmental factors such as the very low ambient pressure and the absence of oxygen on lubrication are discussed. The low pressure causes liquids, and even solids, to boil away, so that their vapour pressure and evaporation rates become important. Evaporation experiments with metals, liquids, greases and solid lubricants are discussed. Silicone oils and silicone-based greases appear to have the lowest evaporative loss among the fluids investigated. Bearing experiments indicate that liquids and greases, when properly shielded, can provide longer bearing lives than bonded solid lubricants or metal platings. Silicone fluids yield the best bearing life, confirming the results of evaporation tests. Life results with bonded solid films are generally poor. Results are considerably better when the solid lubricant is used as a constituent in a solid-composite material. Bearing reliability in space applications may be a problem because considerable life scatter is observed where a particular lubricant or lubrication techniqueis evaluated in multiple tests. Life ratios of 10 were common.
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