Spalling?

To Jay Huebner:

We had some discussion a while back on orbital debris and what would
happen when a fragmentation event occurred. There's a relevant article
on space.com today (c.f.,
http://www.space.com/missionlaunches/junk_iss_020107.html) which states
that,

"
Cosmos 2367 had been the latest of the Cosmos 699 series of
three-metric-ton spacecraft that started space operations in 1974.
For unknown reasons, the spacecraft broke up on November 21. In an orbit
just 19 miles (30 kilometers) above the ISS, the Russian craft busted up
into over 300 large and small pieces. Most fragments were concentrated in
a 124-mile (200 kilometer) to 310-mile (500 kilometer) altitude, while
other bits were tossed into orbits that reached 1000 kilometer altitude.
Approximately 40 percent of the debris were immediately thrown into orbits
that crossed the orbit of ISS.
"

Ron

rmenich@...
11/15/01 05:35 PM

Before I launch into this, let me say that I'm not an orbital mechanics
expert. Here is my rudimentary analysis.

I'd guess what would happen would depend on a number of factors. Suppose

that we have an object in circular orbit 235 miles above the Earth (say,
ISS Alpha), and a second object impacts the first. The natural thing to
ask is at what angle relative to the tangent the second object impacts the

first.

Suppose first that the second object impacts the first in the same
direction as the velocity vector of the first. In that case, most of the

fragments produced by the collision can be expected to have greater
orbital energy than that of the first object, and would hence end up in
orbits with greater semi-major axes than 235 miles. Fragments ejected
directly along the velocity vector would go into elliptical orbits with
perigee equal to 235 miles and apogee greater than 235 miles.

Of course, the opposite could happen and the second object could impact
the first 180 degrees opposite of the velocity vector of the first. In
that case, fragments ejected along the velocity vector of the impacting
object would go into elliptical orbits with apogee equal to 235 miles.
Whether or not the perigee of those orbits brings the fragments down into
the upper reaches of the atmosphere, thus experiencing the aerobraking you

envision, depends entirely on how energetic the collision was in terms of
delta-v.

Yet another possibility is that the second object impacts the first normal

to the velocity vector of the first. In this case, fragments ejected
along the velocity vector of the impacting object would go into elliptical

orbits with semi-major axes equal to 235 miles.

What say you to this analysis?

Ron

"Huebner, Jay" jhuebn@...
11/15/01 05:23 PM

I may indeed "... be mistaken on this topic." But one paint fleck
chipping a shuttle window (not windows) does not seem too serious to me,
as
I know that the Long Duration Exposure Facility had a micro-meteor (or is
it meteoroid?) impact. I am certainly not sure these two are all of the
impacts there have been, but if they are, then the score is one
"industrial"
impact to one "natural" impact. So what does your friend say about
impacts
with the natural background, the meteoroids? That is an important
bench-mark, below which we could never get, even if there were no
satellites.
And I still don't see how two orbiting objects can collide and have
much
mass remain in orbit. "Exploding" does not change that. Exploding a
weapon, say a hand-grenade, from which all metal fragments fly out from
the
center of mass should take those (to hedge a little, maybe I should say
nearly all) fragments out of orbit. The word exploding sounds dangerous
and
destructive, but that is from our terrestrial reference. It might be the
best way to get satellites which can not be brought down in one piece out
of
orbit. I doubt that intuition is very useful here, and that some serious
work is required to settle this question. But maybe all we have to do is
collect data on what happens and we will see.
Sincerely, Jay Huebner at jhuebn@...