Nep

Figure 3. (Left) LDEF's orbit with respect to the Earth and the ecliptic plane. LDEF maintained its geocentric geometry. The main faces are North, South, East, West, Earth and space. Note that the north face normal vector was offset by 8° towards the ram (east) direction and that the space face had a tilt of 1.1° (revolved around the north face normal towards the ram face). This is incorporated into the modelling. (Right) The LDEF data-fit of the space face, and the meteoroid model prediction. Very little orbital debris is expected on the space face, and here we see that the meteoroid model prediction fits very well.

Figure 3. (Left) LDEF's orbit with respect to the Earth and the ecliptic plane. LDEF maintained its geocentric geometry. The main faces are North, South, East, West, Earth and space. Note that the north face normal vector was offset by 8° towards the ram (east) direction and that the space face had a tilt of 1.1° (revolved around the north face normal towards the ram face). This is incorporated into the modelling. (Right) The LDEF data-fit of the space face, and the meteoroid model prediction. Very little orbital debris is expected on the space face, and here we see that the meteoroid model prediction fits very well.

4.3. The results

Figure 3 shows the consideration of the LDEF space face. The diagram (left) reminds us of the LDEF geometry, and it is seen that as the spacecraft orbits (and the orbit precesses) the space face avoids Earth shielding and offers an essentially randomised exposure to space. Figure 3 (right) shows the data-fit for the space face of LDEF compared with the prediction from the meteoroid model described above. The model fits the space face well at all sizes measured (with perhaps a slight underestimation at the smallest sizes). This is a remarkable agreement, and it appears that, considering the uncertainties in the data and modelling procedure (velocity distribution used, impact equation used etc) there is no need whatsoever to re-assess the mean flux distribution of Grün et al. [16]. Thus the 'Grün flux', when applied to an appropriate surface (i.e. one that has had an effectively randomised exposure) appears to represent reality very well indeed.

Referring Figure 3 (left), it is seen the east face points to the spacecraft ram direction, whereas the west face is trailing. The east face would thus be particularly susceptible to debris impacts. The west face could also be struck by debris although it is more limited to eccentric orbits near perigee. Figure 4 shows the data-fits for the west and east faces of LDEF with their respective meteoroid model fits. The fit to the west face is reasonable, although underpredicting at larger sizes. The model fits the east face' at Fmax>30 ^m, although below this, a striking excess flux is apparent, attributable to 'contamination' by space debris particles (see below).

Figure 4. The LDEF data-fits and the meteoroid model predictions, for the LDEF (a) west face, and (b) east face (which is the orbit ram direction). The meteoroid model fits at Fmax>30 ftm although below this, the excess is interpreted as being due to small orbital debris particles.

Was this article helpful?

0 0

Post a comment