Solar cell chemical data

Figure 6. (a) The LDEF 4-face mean data (solar array analogue) has been used with the meteoroid model, to identify the proportion of the impact flux which came from space debris. The data has been converted to Dco. (b) The proportion of debris craters identified from the HST solar array chemical analysis. The error bars account only for the uncertainty due to craters where residues could not be identified.

Graham et al. [63] present analyses of 165 craters on the HST solar array, where most residues can be identified as being either from natural meteoroid or man-made debris impactors. We can use the meteoroid modelling, and the LDEF 4Jface mean solar array analogue to 'predict' the debris/meteoroid ratio for a LEO solar array, by simply subtracting the meteoroid model flux from the 4-face mean. This is shown in Figure 6a, with Fmax converted to Dco for direct comparison with the HST solar array data shown in Figure 6b (again using the Taylor et al. [37] conversion). In Figure 6a, the upper and lower limits come from the upper and lower limits of the LDEF 4-face mean data-fit points (as was shown in Figure 5a). In Figure 6b, the percentage debris is simply defined as the number of 'natural craters' over the 'debris craters'. The 'error bars' shown are produced by assuming that any unidentified craters were either all debris (upper limit) or all meteoroid (lower limit). The values in parentheses refer to the total number of craters in each logarithmic bin.

It is seen in Figure 6 that in general, the results from the LDEF data and meteoroid modelling agree very well with the HST chemical residue data in the sub-mm regime. At smaller sizes, both results appear to show around 80% debris with a crossover to meteoroid domination at around ~100 fim Dco (equivalent to Fmax=30 fim i.e. as was seen in Figure 4b). This agreement is quite remarkable considering that it is derived in different ways and from completely independent data sources. The HST chemical data (Figure 6b) does show an enhancement of debris at Dco>l mm, not seen in the LDEF data. It should be noted that the data is relatively sparse at this size regime, particularly for LDEF, and perhaps not too strong a conclusion should be drawn at this size. However the HST arrays were in space after LDEF was recovered, and so it is also possible that the large particle debris environment suffered a real enhancement at this time.

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