The nearly total absence of air around and within space vehicles has two major implications for tribology. Firstly, oxygen and water vapour are not on hand to repair damaged surfaces, so strong adhesion (welding and galling) between clean degreased materials becomes inevitable if they are unprotected. Secondly, a liquid phase lubricant (e.g. oil or grease) can quickly volatilise or boil away, either directly to space or contaminating the spacecraft, unless the lubricant has sufficiently low vapour pressure and/or is suitably “sealed” to retard molecular effusion. Thus, the space environment impose the use of lubricants that neither volatilise nor creep, and which are not influenced by temperature extremes.
Loading…