Solar Array Data

Although it is undoubtedly an easier task to measure and interpret impacts on ductile materials such as the craters and penetrations on LDEF, the solar arrays of the EuReCa and HST spacecraft offer a valuable complementary source of data from a large area-time product surface. The surfaces have also undergone considerable chemical residue analyses, and so it is useful to compare the data to the meteoroid model, and indeed 'predict' the ratio of the meteoroid to debris flux, for comparison with the chemical analysis data.

The first task is to model the expected exposure to meteoroids for Sun-pointing solar arrays. This is done using the meteoroid model presented above. Although LDEF did not have solar arrays, and clearly did not maintain a Sun-pointing orientation, the data does at least offer a 'solar array analogue', by taking a mean of the space, east, Earth and west faces. This is because Sun-pointing arrays effectively spin with respect to geocentric space, and thus are approximated by the space, east, Earth and west 'LDEF 4-face mean'. The comparison with the meteoroid model and the LDEF 4-face mean solar array analogue is shown in Figure 5a (also shown is the output for an 'apex enhanced' model described in [36,40] which is applicable to non-random exposures; however in this case the isotropic and apex enhanced models are quite similar). As before, for the LDEF east face (Figure 4b) we have good agreement with the model at larger sizes, and an excess attributable to debris at the smaller sizes (Fmax<30 fj,m).

Figure 5b shows data from the EuReCa solar arrays, and also from the TiCCE experiment penetration foils (which were located between the solar direction and the Earth apex direction, and so approximate quite well to the solar array exposure). The source data for the solar arrays is in the form of conchoidal crater diameter Dco (i.e. including the crater shatter zone around the central pit). However this is converted to an equivalent ductile Fmax value by the expression Fmax=(0.3±0.1)Dco defined by Taylor et al. [37]. The plot also includes the meteoroid model fits and the LDEF 4-face mean as in Figure 5a. It is seen that the LDEF 4-face mean solar array analogue agrees with the high reliability

• Soiar arrays (apex enhanced meteoroid model)

• Solar arrays (isotropic meteoroid model)

- Solar arrays (apex enhanced meteoroid model)

Solar arrays (isotropic meteoroid model)

v i

(b)

O EuReCa-Optical (Berthoud [56])

* TiCCE 9.2 iim foil

0 LDEF data 4-face mean

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