Natural and simulated hypervelocity impacts into solar cells

The solar array which was returned to Earth from the Hubble Space Telescope (HST) in 1993, after 3.62 years of space exposure in low Earth orbit (LEO), has offered the opportunity to document populations of natural micrometeoroids and artificial "space debris". Residues from the hypervelocity impact (HVI) of material deposited in 25 individual solar cells from the array have been investigated herein by scanning electron microscopy. The observations have been compared with the results of simulated HVIs into solar cells using known meteorite mineralogies. This has permitted assessment of the probability of retention for residue materials derived from HVI by well-characterised mineral species. The simulation experiments have thus far suggested that some of the textural features observed in impact residues are dependent on the nature of the individual mineral components within the original impactor. Furthermore it transpires that compounds containing volatile elements, such as Ca (from calcium carbonate), can be preserved as near-intact fragments explosively emplaced in an impact crater. Such unusual particles should not always be dismissed as simply contamination products if observed in LEG-derived HVIs.