Tribology Experiments in Space

Brief history of tribology experiments in space is described. Tribological performance in a high vacuum was a great concern in early stage of space development, and it was urgent task to verify whether the actual space environment can be simulated using ground-based vacuum facilities from tribological viewpoint. Some friction tests as well as bearing tests were carried out on board satellites in 1960s, and the conclusion was that the results of space experiments was very similar to those of ground-based comparison experiments. In 1980s, however, Space Shuttle flown in Low Earth Orbit (LEO) revealed a new problem; oxidization by active atomic oxygen, which is more than 90% constituent in the environment. Some types of solid lubricants might be oxidized, and thus lost tribological effectiveness. Efforts to clarify the effect of LEO environment on solid lubricants, as well as to simulate LEO environment properly, have been devoted including space experiments. Recent tribology-related space experiments are briefly reviewed.