Further attempts to constrain the nature of the impact residues in the HST solar array panels

An analytical study has been carried out on an impact feature within a solar cell from the Hubble Space Telescope Solar array. Optical investigation of the feature in question showed that it was the result of a partially penetrating impact, and as such might expect to record evidence of the particle responsible for the damage. Chemical analyses obtained by X-ray emission elemental mapping identified a residue in part of the inner impact crater. The residue was found to contain Fe, Ti, K, Ca, Si, Mg, Na and minor Ce. The presence of Mg, Fe and Ti (elements foreign to the solar cell), suggested an impact residue of natural or man-made origin. Subsequent detailed analysis showed Fe and Mg in concentrations of about 10% with Ti in only limited amounts, implying that the residue might be from a particle of natural origin. Quantitative X-ray micro-analysis of the residue indicated it was chemically similar to a pyroxene, which suggests that the impact residue was a natural micrometeoroid. Partially-penetrated impacts are common features in solar cell materials (3 out of 6 randomly selected samples). Although conditions present in the selected cell are rare, the essential feature was the limited deposition of material from upper layers of the cell. This created an almost homogenous substrate which made the identification of extraneous material easier.