So, I'm watching Gravity for the third time, I absolutely love the movie, but something bothers me every time I see the giant debris cloud hurtling through space. Now granted most of my experience in orbital mechanics comes from playing Kerbal Space Program so I'm no rocket scientist. But as I understand it two objects in a circular orbit around (the earth) at the same altitude are going to be traveling at roughly the same relative speed. So it would seem to me that for the debris cloud to behave as it did in the movie it would have to be moving in a retrograde orbit. It just seems to me that the way that Kessler syndrome is depicted in the movie isn't entirely realistic, which of course seems intuitive, considering it's a movie and had to be entertaining. But it does bring to mind some questions of how a more realistic and less dramatic representation of Kessler syndrome would look. I'm approaching this more like a thought experiment, since my understanding of the math involved is, quite frankly, not very good. So, in order for an impact to occur, at least one of the objects would have to be in an eccentric orbit, at the same altitude but in different directions, or a combination of the two. Looking at the former, its my understanding that there aren't very many man-made satellites in highly eccentric orbits. So, for the most part, it seem to me that objects travelling in roughly the same direction at roughly the same altitude aren't going to be travelling very fast relative to one another (maybe a few m/s difference? I'm not really sure) Since we're not dealing with billiard balls here but (relatively) lightweight material, not all of the force imparted from an impact is going to translate directly to change in velocity. So, in short, I guess what my question boils down to is what kind of numbers are we looking at here? I imagine a Kessler syndrome scenario isn't going to play out in the time it takes to watch a feature length film. But for things that didn't use to crash into each other to start crashing into each other something is going to have to change. But how much change are we talking? You read an article where they say 'satellites are flying through space at 22,000km/h', but that seems to leave out the big picture. They're travelling at that speed relative to the earth, not each other. Anyway, some elaboration would be appreciated. Thanks, guys.