Long Duration Exposure Facility

NASA's Long Duration Exposure Facility, or LDEF (pronounced "eldef"), was a cylindrical facility designed to provide long-term experimental data on the outer space environment and its effects on space systems, materials, operations and selected spores' survival. It was placed in low Earth orbit by Space ShuttleChallenger in April 1984. The original plan called for the LDEF to be retrieved in March 1985, but after a series of delays it was eventually returned to Earth by Columbia in January 1990.

It successfully carried science and technology experiments for about 5.7 years that have revealed a broad and detailed collection of space environmental data. LDEF's 69 months in space provided scientific data on the long-term effects of space exposure on materials, components and systems that has benefited NASA spacecraft designers to this day.