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.

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.

[3] It successfully carried science and technology experiments for about 5.7 years that have revealed a broad and detailed collection of space environmental data.

[6] The LDEF structure shape was a 12 sided prism (to fit the shuttle orbiter payload bay), and made entirely from stainless steel.

Therefore, propulsion or other attitude control systems were not required, making LDEF free of acceleration forces and contaminants from jet firings.

An FRGF and an active (rigidize sensing) grapple used to send an electronic signal to initiate the 19 experiments that had electrical systems.

Some of the experiments had a cover that opened after deployment and was designed to close after about a year,[10] e.g., Space Environment Effects (M0006).

[4][3] Interstellar gases also would be trapped in an attempt to find clues into the formation of the Milky Way and the evolution of heavier elements.

[20] While LDEF was still attached to the RMS arm, an extensive 4.5 hour survey photographed each individual experiment tray, as well as larger areas.

[20] Nevertheless, shuttle operations did contaminate experiments when concerns for human comfort out-weighed important LDEF mission goals.

[4] With LDEF still in its bay, Columbia was ferried back on the Shuttle Carrier Aircraft to the Kennedy Space Center on January 26.