NASA Long Duration Exposure Facility (LDEF)

1978 - 1990

Long Duration Exposure FacilityProject overview

NASA's Long Duration Exposure Facility (LDEF) was designed to provide long-term data on the space environment and its effects on space systems and operations. It successfully carried science and technology experiments that have revealed a broad and detailed collection of space environmental data. The LDEF concept evolved from a spacecraft proposed by NASA Langley Research Center (LaRC) in 1970 to study the meteoroid environment, the Meteoroid and Exposure Module (MEM).

LDEF had a nearly cylindrical structure, and its 57 experiments were mounted in 86 trays about its periphery and on the two ends. It measured 30 feet by 14 feet and weighed 21,500 pounds with experiments. It remains one of the largest payloads deployed by the Shuttle. The experiments involved the participation of more than 200 principal investigators from 33 private companies, 21 universities, seven NASA centres, nine Department of Defense laboratories and eight foreign countries. The post-flight special investigations and continued principal investigator research have made the total number of investigators between 300 - 400.

Long Duration Exposure FacilityLDEF was deployed in orbit on April 7, 1984 by the Shuttle Challenger. The nearly circular orbit was at an altitude of 257 nautical miles and an inclination of 28.4 degrees. Attitude control of the LDEF spacecraft was achieved with gravity gradient and inertial distribution to maintain three-axis stability in orbit. Propulsion or other attitude control systems were therefore not required, and LDEF was free of acceleration forces and contaminants from jet firings.

LDEF remained in space for 5.7 years and completed 32,422 Earth orbits, and this lengthed stay increased its scientific and technological value toward the understanding of the space environment and its effects. It experienced one-half of a solar cycle, as it was deployed during a solar minimum and retrieved at a solar maximum.

LDEF was retrieved on January 11, 1990 by the Shuttle Columbia. Its orbit had decayed to 175 nautical miles, and it was little more than one month away from reentering the Earth's atmosphere. Columbia returned to Edwards Air Force Base and was ferried back to KSC on January 26, 1990.

After processing activities, post-retrieval research activities at NASA Kennedy Space Center (KSC) for each tray included a radiation survey, infrared video survey, meteoroid and debris impact survey, contamination inspection and extensive photo documentation. Trays and experiments were shipped or hand-carried directly from KSC to the investigators' laboratories.

Infrared Multilayer Laboratory contribution

Long Duration Exposure FacilityThe University of Reading experiment to assess the exposure of space radiation on high-performance Infrared Multilayer filters and optical materials comprised a total of 46 individual components subdivided between two tray locations on the spacecraft. One location was positioned to be continuously facing Earth on tray number G12 whilst the other tray was positioned to continuously face space on the leading edge of the vehicle in tray number B08. Each tray was designed to maximise the exposure of the full aperture of each sample to the complete range of space radiations and temperature excursions received by the spacecraft.

The samples occupied 1/8th of the Earth facing tray G12 measuring 37.5 cm length x 20.5 cm width and 7.6 cm depth, and 1/12th of the space facing tray B08 measuring 46.7 cm length x 20.5 cm width and 7.6 cm depth.

Long Duration Exposure FacilityThe 46 components flown were each housed in BS.L93 chromic anodised aluminium alloy circular holders and mounted in 6061-T6 chromic anodised aluminium alloy base plates. Tray B08 contained 26 components, the other 20 were housed in tray G12.

Each of the aluminium substrate holders was designed for maximum mechanical stability and to ensure intimate thermal contract providing a uniform temperature distribution across the complete exposed aperture.

The samples were retained in their holders using disc springs and circlips located directly behind a BS.L93 chromic anodised aluminium backing piece. Thermal contact was ensured by using lead washers located either side of the substrate. The holders were then retained in the base plate using a disc spring and circlip attached to a recess in the outside of the holder.

A small pressure release hold was located in the centre of each backing piece to minimize the pressure differential across the substrate and prevent substrate flexing or deformation.

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