Long Duration Exposure Facility

Researchers identified the potential of the planned Space Shuttle to deliver a payload to space, leave it there for a long-term exposure to the harsh outer space environment, and retrieve it for analysis on a separate mission. The LDEF concept evolved from a spacecraft proposed by NASA's Langley Research Center in 1970 to study the meteoroid environment, the Meteoroid and Exposure Module (MEM). but after the unintended extension of mission 1 the structure itself was treated as an experiment and intensively studied before being placed into storage. ==Launch and deployment==

The STS-41-C crew of deployed LDEF on April 7, 1984, into a nearly circular orbit at an altitude of 257 nautical miles. ==Design and structure==

The LDEF structure shape was a 12 sided prism (to fit the shuttle orbiter payload bay), and made entirely from stainless steel. There were 5 or 6 experiments on each of the 12 long sides and a few more on the ends. It was designed to fly with one end facing earth and the other away from earth. This activated the Experiment Initiate System (EIS) which sent 24 initiation signals to the 20 active experiments. There were six initiation indications which were visible to the deploying astronauts next to the active grapple fixture. Engineers originally intended that the first mission would last about one year, and that several long-duration exposure missions would use the same frame. In the event the facility was actually used for a single 5.7-year mission. == Experiments ==

The LDEF facility was designed to glean information vital to the development of the Space Station Freedom-cum-International Space Station and other spacecraft, especially the reactions of various space building materials to radiation, extreme temperature changes and collisions with space matter. Some of the experiments had a cover that opened after deployment and was designed to close after about a year, e.g., Space Environment Effects (M0006). Furthermore, interstellar gases would be trapped in an attempt to find clues into the formation of the Milky Way and the evolution of the heavier elements. the German Solar cell study (S1002), One experiment (S0069) used a 4-track magnetic tape module not as part of an EPDS. At least one of the on-board experiments, the Thermal Control Surfaces Experiment (TCSE), used the RCA 1802 microprocessor. ==Experiment results==

EXOSTACK In the German experiment EXOSTACK, 30% of Bacillus subtilis spores survived the nearly 6 years exposure to outer space when embedded in salt crystals, whereas 80% survived in the presence of glucose, which stabilize the structure of the cellular macromolecules, especially during vacuum-induced dehydration. If shielded against solar UV, spores of B. subtilis survived in space for up to 6 years, especially if embedded in clay or meteorite powder (artificial meteorites). The data may support the likelihood of interplanetary transfer of microorganisms within meteorites, the so-called lithopanspermia hypothesis. Space seeds germinated sooner and grew faster than the control seeds. They were also more porous than terrestrial seeds. ==Retrieval==

At LDEF's launch, retrieval was scheduled for March 19, 1985, eleven months after deployment. Schedules slipped, postponing the retrieval mission first to 1986, then indefinitely due to the Challenger disaster. After 5.7 years its orbit had decayed to about and it was likely to burn up on reentry in a little over a month. It was finally recovered by on mission STS-32 on January 12, 1990. Columbia approached LDEF in such a way as to minimize possible contamination to LDEF from thruster exhaust. 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. Columbia landed at Edwards Air Force Base on January 20, 1990. With LDEF still in its bay, Columbia was ferried back on the Shuttle Carrier Aircraft to the Kennedy Space Center on January 26. Special efforts were taken to ensure protection against contamination of the payload bay during the ferry flight. Between January 30 and 31, LDEF was removed from Columbia's payload bay in KSC's Orbiter Processing Facility, placed in a special payload canister, and transported to the Operations and Checkout Building. On February 1, 1990, LDEF was transported in the LDEF Assembly and Transportation System to the Spacecraft Assembly and Encapsulation Facility – 2, where the LDEF project team led deintegration activities. ==See also==