Physics
Scientific paper
Aug 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992stin...9232541.&link_type=abstract
Progress Report, 15 Feb. - 14 Aug. 1992 Washington Univ., Saint Louis, MO. Center for the Space Sciences and Physics Dept.
Physics
Chemical Composition, Contamination, Foils (Materials), Hypervelocity Impact, Long Duration Exposure Facility, Micrometeoroids, Residues, Secondary Ion Mass Spectrometry, Space Debris, Abundance, Embrittlement, Failure, Fractionation, Isotopes, Leading Edges, Plastics, Refractories, Simulation, Trailing Edges
Scientific paper
Numerous 'extended impacts' found in both leading and trailing edge capture cells have been successfully analyzed for the chemical composition of projectile residues by secondary ion mass spectrometry (SIMS). Most data have been obtained from the trailing edge cells where 45 of 58 impacts have been classified as 'probably natural' and the remainder as 'possibly man-made debris.' This is in striking contrast to leading edge cells where 9 of 11 impacts so far measured are definitely classified as orbital debris. Although all the leading edge cells had lost their plastic entrance foils during flight, the rate of foil failure was similar to that of the trailing edge cells, 10 percent of which were recovered intact. Ultra-violet embrittlement is suspected as the major cause of failure on both leading and trailing edges. The major impediment to the accurate determination of projectile chemistry is the fractionation of volatile and refractory elements in the hypervelocity impact and redeposition processes. This effect had been noticed in simulation experiment but is more pronounced in the Long Duration Exposure Facility (LDEF) capture cells, probably due to the higher average velocities of the space impacts. Surface contamination of the pure Ge surfaces with a substance rich in Si but also containing Mg and Al provides an additional problem for the accurate determination of impactor chemistry. The effect is variable, being much larger on surfaces that were exposed to space than in those cells that remained intact. Future work will concentrate on the analyses of more leading edge impacts and the development of new SIMS techniques for the measurement of elemental abundances in extended impacts.
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