Particulate Detection in the Near Earth Space Environment Aboard the Long Duration Exposure Facility Ldef: Cosmic or Terrestrial?

Abstract

Examination of surfaces exposed for more than five and a half years, from detectors with unique attitude stabilisation relative to the orbital velocity vector, offers scope for examining definitively the sources of hypervelocity space particulates. Surfaces reveal discrete crater morphologies, crater size distributions and incident flux distributions. Discrete crater studies will later also reveal the chemistry of residues which can, especially via the capture cell principle, lead to elemental analysis of micron dimensioned particles.First analyses of the flux data from the thin foil perforation experiments (MAP) involve a study of the statistics of the forward (ram) direction, the rear (trailing) direction and the space pointing direction. Modelling of the dynamics of geocentrically bound and unbound orbits yields evidence that the characteristics of the particles, and hence probably their source, change over the particle size range measured by the experiment. Smaller particles (< 1 μm diameter) have lower velocities which could include geocentrically bound particulates, whereas the larger particles (5-10 μm diameter) can be identified with “cosmic” particles of interplanetary or interstellar origin.

Study of Cosmic Dust Particles on Board LDEF and MIR Space Station

“…The data indicate the presence of particles with a diameter of a few tenths of microns (mass of 10"" gm) in earth bound orbits. Data from IDE experiment on LDEF are consistent with these results (Singer et al,1990), as well as measurements reported by Singer (Singer and Stanley,1980 The size distribution shows a good agreement with comparable near-earth data obtained by McDonnell (McDonnell et al 1991); flux on the west face of LDEF is about 20 times lower than on the east face, for large particles. Most of the particles impacting this face should be interplanetary dust particles, not orbital debris.…”