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LDEF experiment background

The NASA Long-Duration Exposure Facility (LDEF) was a free-flying satellite designed to provide an economical means of achieving space exposure in the Low Earth Orbit (LEO) of experiments that could benefit from post recovery measurements of the retrieved hardware. The LDEF experiment structure was designed and fabricated at NASA Langley in the late 1970's as a passive reusable satellite for planned repeat missions using the two-way transport capability provided by the Space Shuttle. It is a 4.3 meter diameter by 9.1 meter long aluminium cylindrical structure with the cross section of a 12-sided regular polygon.

Experiments were attached to the exterior of the structure in self contained experiment trays, each tray measuring 86.4cm x 127cm which could be further sub-divided to accommodate smaller experiments. The 9709Kg facility was placed in orbit by the Shuttle Challenger on 7th April 1984 at a 482km circular orbit with a 28.4° inclination relative to the equator. The structure was gravity-gradient stabilised and mass loaded so that one end of the LDEF was always pointed at Earth and one side (leading edge) was always oriented into the orbit path (sun rising) ram direction. In orbit, the orientation of the structure ended up rotated around its long axis such that the leading edge was offset from the ram direction by about 8°. This orientation remained constant throughout the entire operational lifetime of the mission. LDEF also used a viscous damper which was designed to gradually eliminate any destabilising oscillations caused during deployment.

Duration of the exposure was originally anticipated to last for a period of 10-12 months for retrieval in early 1985. Due to Shuttle re-scheduling and the loss of Challenger, LDEF was not retrieved until the 12th January 1990 after 5 years and 8 months (2106 days) and 32,422 orbits in low Earth orbit, by which time the orbit had degraded from 482km to 340km. This extended duration presented a unique opportunity to study the long term effects of space exposure on the filters and substrate materials flown.

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Effects of the space environment on infrared filters and materials