Long Duration Exposure Facility (LDEF)

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Long Duration Exposure Facility (LDEF)

The Long Duration Exposure Facility (LDEF) project, originally called the Meteoroid and Exposure Module, was begun in 1970. Conceived and managed by the National Aeronautics and Space Administration's (NASA) Langley Research Center in Hampton, Virginia, the LDEF was designed as a large structure on which various tests of systems and materials could be carried out. One of its most important functions was to gather data on meteoroids , radiation, and other space hazards.

The LDEF was a 9-meter-long (30-foot-long) hexagonal-shaped structure designed to fit snugly into the space shuttle orbiter's cargo bay. The research programs involved corporations, universities, and U.S. and foreign governments. The LDEF was a platform both for engineering and systems development studies and for pure scientific research.

One goal of the LDEF program was to see how a wide variety of materials, such as plastic and glass coverings for solar power (photovoltaic ) cells, would react to spending a long time in low Earth orbit (LEO). The stability of certain plastics was tested. Some of the polymers were found completely unsuitable for use in space.

Another goal was to measure the number and composition of meteoroids, debris, and radiation in LEO. The LDEF was a way for NASA to find out what sort of materials would be needed in any future space stations or satellites that would spend years in LEO. The experiments were mounted on eighty-six separate trays, normally one experiment per tray. Some experiments were carried out using multiple trays, such as the Space Environment Effects on Spacecraft Materials Experiment, which used four different trays, and the High Resolution Study of Ultraheavy Cosmic Rays, which used fifteen.

The LDEF was launched inside space shuttle Challenger on mission STS 41-C in April 1984. Commanded by Robert Crippen, this was the twelfth shuttle mission. The LDEF was placed in orbit at an altitude of 442 kilometers (275 miles) above Earth. It was intended that the LDEF would stay in orbit for just one year, but because of the Challenger disaster in January 1986, the facility was not recovered until January 1990. Thus, it ended up spending five years and seven months in space.

When it was picked up by the space shuttle Columbia, the LDEF was only a few weeks away from falling into Earth's atmosphere and burning up. Over the years, its orbit had decreased to about 280 kilometers (175 miles). As it moved closer to Earth, it also became closer to the upper layers of the planet's atmosphere. Thus, the particles of the atmosphere began to strike it and reduce both its speed and its altitude. The closer it got to Earth the faster it began to fall. The STS-32 mission, commanded by Dan Brandenstein, got there just in time.

Back on Earth, NASA found that the silicon-based adhesives they used on the LDEF spacecraft (as well as on the shuttle) had let off a form of gas that was transformed, by exposure to atomic oxygen, into silicates (SiO₂) and had contaminated some of the surfaces of the LDEF. This showed that there is a danger of silicate contamination of surfaces that have critical optical needs, such as windows, solar cells, and mirrors.

Following completion of the LDEF project, NASA's Langley Research Center built the Modular International Space Station Experiment. This is a test facility, about the size of a suitcase, which will continue the work started by the LDEF. A new wave of Passive Experiment Containers will be attached to the International Space Station and will provide data for the next generation of spacecraft.

see also Challenger (volume 3); Exploration Programs (volume 2); Space Shuttle (volume 3).

Taylor Dinerman