NASA's long duration exposure facility (LDEF) was the first example of a retrievable carrier, a spacecraft designed to be deployed in space for extended periods and then recovered. Unlike the European Space Agency's much more sophisticated Eureca carrier, the LDEF was a one-off facility, designed primarily to investigate the effects on materials of prolonged exposure to the space environment. It was fitted with grapple fixtures so that it could be deployed into space and retrieved using the shuttle's 'crane', the remote manipulator system (RMS) arm. Managed by the Langley Research Center, the LDEF was deployed from Challenger on the STS-41C mission on April 7, 1984, and was intended to remain in orbit for about a year. But delays in shuttle launches and then the halt in the shuttle programme after the Challenger disaster, postponed its recovery until January 9, 1990. Then it was plucked from orbit by Columbia's astronauts on STS-32 and returned to Earth. Fifty-seven experiments were flown on the LDEF, involving some 200 investigators from NASA centres, universities, commercial companies, the Department of Defense and eight foreign countries. The experiments were centred on four areas: materials and structures, power and propulsion, science and electronics, and optics. They gathered information on such things as space radiation, meteoroids, contamination, space debris and the effect of radiation on organisms such as shrimp eggs and plant seeds. Perhaps the most valuable data related to materials performance under long exposure. This should prove invaluable for designers of the upcoming space station Freedom. During the long mission, the meteoroid detector on the LDEF registered hits by 15,000 particles. These particles included identifiable debris from earlier shuttle missions and other launch vehicles. The various paints and polymers used to coat the LDEF suffered varying degrees of darkening, erosion and deterioration in physical properties. Exposure to space radiation had made some of the metal structure radioactive. Very few electrical or mechanical failures occurred on the LDEF. The electronic systems performed well, as did the tape recorders. No loss of data occurred on recorded tapes. Among the living organisms on board, the shrimp had a shortened life span and exhibited some genetic mutation because of the radiation they received. Plants grown from space-exposed seeds had variegated leaves, with some parts lacking chlorophyll. Students throughout the USA took part in experiments to study the growth of the 12.5 million tomato seeds carried on the LDEF in a project appropriately named SEEDS (space exposed experiment developed for students).
