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 micrometeo roids and artificial "space debris". Residues from the hypervelocity impact (HVI) of material deposited in 25 individual solar cells from the array ha ve been investigated herein by scanning electron microscopy. The observatio ns have been compared with the results of simulated HVIs into solar cells u sing known meteorite mineralogies. This has permitted assessment of the pro bability of retention for residue materials derived from HVI by well-charac terised mineral species. The simulation experiments have thus far suggested that some of the textural features observed in impact residues are depende nt on the nature of the individual mineral components within the original i mpactor. Furthermore it transpires that compounds containing volatile eleme nts, such as Ca (from calcium carbonate), can be preserved as near-intact f ragments explosively emplaced in an impact crater. Such unusual particles s hould not always be dismissed as simply contamination products if observed in LEG-derived HVIs. (C) 1999 Elsevier Science Ltd. All rights reserved.