FIGURE 4-5 Meteoroid environment at 500 km altitude.

SOURCE: Grün et al., 1985.

than the average LEO spatial density. Although it is unclear how well the distribution of the uncataloged large and medium-sized debris population correlates with the tracked population, it is likely (considering the known sources and perturbing forces) that the average spatial density of these populations is also much lower in HEO than in LEO.

For GEO spacecraft, the chance of collision with cataloged objects decreases sharply with the distance from the geostationary orbit. Figure 4-6 shows how the cataloged space object flux (and thus the probability of collision with a cataloged object) in the GEO region varies as a function of altitude above and below GEO. The flux drops by almost a factor of ten about 50 km above or below the exact geostationary orbit and is approximately two orders of magnitude lower only 500 km above or



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