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A paper (Active Debris Removal: EDDE) contained this diagram of orbital debris. This is the angle seen by the spacecraft horizontally and altitude vertically.

Space Debris

What are the reasons for the lines and clusters of objects on this scale?

Looking at lines around 1000 km and 1500 km, I'm wondering if a part of it is arbitrary numerology. That is, scientists picking 1000 km because it's a round number.

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    Also "in-plane angle" probably does not describe inclination, rather something like true anomaly. –  Aug 01 '13 at 17:28
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    First guess: that's where we put them! If you could cross-reference those debris with the mission they originated from, I think you'd find the missions themselves occurred at those altitudes. The debris that didn't experience orbital decay hung around in their orbits. Why at those orbits? Round numbers: 1000, 750, 1500. Mmmm nice round numbers. – Jesse Smith Aug 01 '13 at 17:29

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The two bands near ~750km and ~975km (the more pronounced one) correspond with two large debris events: the Fengyun 1C ASAT test occurred near -- but not quite at, although it's hard to tell from this plot -- the higher altitude (Gabbard plot here (PDF warning)), and the Iridium Cosmos collision occured at 789 km.

As for the higher band, I'm not sure, but some quick Googling produces this relatively recent paper (from 2005) describing unknown debris objects near 1400km.

I'll add that "round numbers are nice" is likely not a reason for this, as orbit design is a relatively complex process, and mission planners rarely (if ever) enjoy the flexibility to just choose a number they like for altitude.

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