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Page Content: William H. Kinard
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The Long Duration Exposure Facility (LDEF) carried over 10,000 materials specimens, as well as a multitude of hardware elements. Some specimens were exposed to the space environment on the outer surface of LDEF, while others were positioned internally or shielded. Additionally, some experiments had time-controlled exposures. Over half of the exposed surface of LDEF consisted of chromic anodized aluminum and silver Teflon thermal blankets. The remaining area consisted of virtually every basic type of material considered for optical, thermal, mechanical, electrical, or other systems on future spacecraft.
The Materials Special Investigation Group (MSIG) was chartered to examine LDEF materials and hardware not investigated as part of experiment post-retrieval activities, and to database LDEF materials data and convey materials findings to interested organizations. The MSIG also assumed the responsibility of defining LDEF's atomic oxygen and solar exposures, and identifying both particulate and molecular contamination levels around the spacecraft. An objective of the MSIG was also to suggest additional evaluations of experiment materials that may not have been part of the original experiments' scope, but that have relevance to comprehensive materials investigations.
The LDEF MSIG has produced a comprehensive set of reports and databases relative to their studies. In the remainder of this overview section, portions of the MSIG final report on LDEF Materials, "Analysis of Materials Flown on the Long Duration Exposure Facility: Summary of Results of the Materials Special Investigation Group," is included.
The LDEF results have become the baseline for understanding long-term exposure to the low-Earth orbit (LEO) environment for the following reasons:
Inorganic thermal-control paints, anodized aluminum and silverized Teflon thermal-control blankets maintained their optical properties, and thus, their thermal control function. Organic materials such as Mylar, Kapton, paint binders, and bare composites showed the expected severe erosion and degradation under atomic oxygen exposure. Coated composite materials survived and generally maintained their mechanical properties.
|1.||The stability of the LDEF orientation during flight allowed a precise definition of environments around the spacecraft and an indication of performance of specific materials as a function of exposure level.|
|2.||The spacecraft was exposed to a variety of space environments over an extended period of time.|
|3.||A very large quantity and variety of materials were examined upon LDEF's return.|
|4.||Even though LDEF was launched in 1984, many materials flown are still essential for use on spacecraft, and evaluation of their performance is technologically significant.|
|5.||LDEF results confirmed the good performance of a number of materials, components, and systems.|
|6.||The collection of on-orbit and post-flight photographs are extensive and are an extremely valuable archive.|
|7.||LDEF experimental results verified the models used to predict atomic oxygen exposure levels.|
|8.||A collection of particulate debris was observed trailing LDEF as the Shuttle approached for retrieval. Vapor-deposited aluminum backing from failed thermal-control blankets on the leading edge of the spacecraft was the apparent source of the particles. The particles appeared to be spinning as individual particles periodically reflected sunlight into the camera.|
Due to the extended mission life, some thin polymeric films and blanket materials were virtually destroyed and created on-orbit debris which were distributed over adjacent surfaces. A low-density particulate debris cloud collected in LDEF's wake. Severe darkening from UV-polymerized molecular deposits was observed around vent paths from the interior of the spacecraft.
Materials Special Investigation Group