Long Duration Exposure Facility (LDEF) A NASA satellite that was deployed from an orbiting space shuttle in Apr. 1984 and remained in orbit until retrieved by the shuttle in Jan. 1990, long after its scheduled retrieval after nine months. Its 57 experiments measured the effects of prolonged exposure of biological and electronic systems to the environment of space, or were studies requiring long exposures. For example, they recorded the quantity of artificial debris striking the satellite, the frequency of meteoroid impacts, levels of ultraviolet radiation, and concentrations of highly corrosive atomic oxygen; the whole spacecraft structure was examined in great detail, providing information that was to influence the design of future spacecraft. There were also major studies on cosmic rays.