Why is orbital debris such a concern?

[Voyager55]

Why is Orbital debris such a concern they always talk about on the ISS? Anything that even has a remote chance of hitting the ISS would need to be at the same altitude as the ISS,anything at the same altitude as the ISS would need relatively the same speed as the ISS (Give or take 5-15 Mph) How does debris travelling a relative 10 Mph pose any threat? (Solar Panels just maybe but I just can't see it) And is my logic about the speed and altitudes even sound? Well I just thought about retrograde debris,but doesn't the USA launch all space flights to the East?

[RulerOfNothing]

Actually, orbital debris is not always in a circular orbit, so it is possible for debris in more eccentric orbits to collide with the ISS or other satellites with a much higher relative velocity.

[Yourself]

Also not all orbits have the same inclination. Inclination is really what makes it a big deal. If the inclination of two objects differs by just one degree in LEO, the relative velocity between them at the collision point will be about 130 m/s. Now consider that the ISS has an orbital inclination of 51.6°. Anything in a similar equatorial orbit (with inclination 0°) will have a relative velocity of about 6.7 km/s.

[PakledHostage]

Not to mention that, even if the debris were in an orbit with the same perigee, apogee and inclination, it could be crossing the ISS' orbit by as much as 90 degrees (assuming both are prograde). That'd give the debris a relative velocity of roughly 11 km/s.

Edit: Ninja'd by yourself... Or was it myself? Or am I loosing my mind?

Edited June 23, 2013 by PakledHostage
clarified

[Themohawkninja]

Not only all of what is mentioned above, but if you've ever noticed in the loading screen for KSP, the words "ablating cascades" appear. That is referring to Ablation Cascade. Think of it as the space version of the Cold War's Domino Theory.

[Unit One]

Also, a BUNCH of debris is in polar orbit.

This destroyed a perfectly good Iridium satellite in 2009 (Though, in this case the Iridium satellite was in polar orbit)

Space Shuttle damage

More Space Shuttle damage

[Voyager55]

Thanks guys,your comments were quite helpful.