Spalling?

> I have a question about "spalling", as in "space junk is a huge problem
> because it is in orbit; and it self amplifies due to a process called
> spalling." I agree "Very little natural
> debris will be in orbit... " but if one piece of orbiting material hits
> another, in order for both to stay in orbit don't they have to have very
> "tight" trajectories in both directions and speed coming out of the
> collision to stay in orbit?

If atleast one of the bodies is already in orbit and the impact
generates a particle that is travelling at only slightly different
velocity than the orbiting body, then the resulting particle will
still be in orbit, in fact almost the same orbit, and the orbits
intersect in two places for a sufficiently small perturbation.

> I would think after the collision, assume no
> new pieces just to make this simple, both would likely be in orbits which
> would take them into the atmosphere within an orbit, and so they would soon
> be gone. Thus collisions between orbiting debris should help clean out the
> debris.

That certainly happens.

But the problem isn't between orbiting debris, it's between
orbiting debris and spacecraft.

Each collision causes a spray of new particles to be produced,
atleast some of which are likely to still be in fairly stable
orbit- the amount of orbiting debris goes up after a collision
(its an exponential process, but at the moment enough material is
decaying from orbit that the runaway point is still a way off.)

> but I think this like "beaming people" on star
> trek, not taken seriously by scientist.

I believe you may be mistaken on this topic. My understanding is
that this is indeed a potentially serious issue. Indeed the Space
Shuttle has suffered damaged windows from this, although in that
case the window did not fail, thankfully- it was a very tiny fleck
of paint.

A friend of mine works as a space weapons researcher and for what
little he would say, they have to take this very seriously indeed-
exploding weapons or satellites in space could have devastating
effects for hundreds of years.