Abstract In the Microabrasion Foil Experiment (MFE) flown onboard Shuttle flight STS-3 as part of the OSS-1 scientific payload, four hypervelocity perforation events were recorded by the capture-cell array. Previous investigations /1/ of hypervelocity craters on Skylab IV windows have suggested the presence in near-Earth orbit of a significant population of man-made debris in the form of aluminium oxide spheres from rocket thruster firings. Cosmic dust investigators on the first LDEF mission (launched in April 1984) have expressed concern over the possibility of ‘contamination’ by these Al2O3 particles. For Al2O3 particles in near-Earth orbit the expected impact velocities are of the order of 7–10 kms⁻¹. At a velocity of 10 kms⁻¹, the three near-marginal MFE events are attributed to particles −2μm in diameter and the largest perforation (23μm diameter) to a particle 4–10μm in diameter. Morphological evidence from the three near-marginal events clearly indicates a low density (1–3 g.cm⁻³) for the impacting projectile which is not entirely consistent with a density of ρ=3.97 g.cm⁻³ for aluminium oxide. Chemical analysis shows silicon enhancement near all crater rims and also calcium for the larger crater. The flux rate deduced for an incident particle mass >1.8×10⁻¹²g is 2.6×10⁻⁵ m⁻².s⁻¹ corrected for Earth shielding. The interplanetary flux at this mass has been placed at 1.0×10⁻⁴ m⁻².s⁻¹, and hence if the MFE craters were to be considered caused by aluminium oxide, our ‘natural’ particle flux would be a factor of −4 below the interplanetary figure. Considering the additional effects of gravitational enhancement near the Earth, the data suggests that Al2O3 contamination is not a serious threat to the collection and analysis of at least the smaller craters in 5μm foil.