MICROPARTICLE POPULATIONS AT LEO ALTITUDES - RECENT SPACECRAFT MEASUREMENTS

Data from satellite impact experiments and the scanning of recovered s pacecraft surfaces and solar cells offer an extended time base for exa mining, using a consistent methodology, microparticle fluxes at low Ea rth orbital (LEG) altitudes. Revised estimates of the ratio of natural micrometeorites to space debris at micrometer dimensions at similar t o 500 km altitude show that the debris population is not as dominant a s previously believed. New data show that, despite a predicted growth in the debris population, the particle flux has not changed appreciabl y in this size regime over the period 1980-1994., Of penetrations of s pacecraft surfaces of a 4 to 5 mu m thickness 18 (+9)/(-6)% are due to interplanetary meteoroids, whereas above similar to 30 mu m thickness the interplanetary component dominates. Results of studies of atmosph eric drag depletion of orbital components, confirmed by flux data at d iffering altitudes, show that at altitudes of similar to 240 km the me teoroid population dominates even at micrometer sizes due to the extre mely short lifetimes of orbital particles. Exposure of detectors in su ch low orbits represents an opportunity to sample the interplanetary m eteoroid population without contamination from space debris. (C) 1997 Academic Press.