Re: Pentagon to Shoot down Spy Sat

John Park wrote:
Sylvia Else (sylvia@xxxxxxxxxxxxxxxxxxx) writes:
Rand Simberg wrote:
On Sun, 24 Feb 2008 10:51:22 +1100, in a place far, far away, Sylvia
Else <sylvia@xxxxxxxxxxxxxxxxxxx> made the phosphor on my monitor glow
in such a way as to indicate that:

It doesn't matter whether it seems that way to you or not. You are
mistaken.
Can you justify that claim by analysis?

Rather than analysis, let's examine history. In prior satellite
reentries, typically nothing substantial hits the ground *except*
propellant tanks (and other tanks). See:

http://www.aero.org/capabilities/cords/faq3.html
http://orbitaldebris.jsc.nasa.gov/reentry/recovered.html
http://commons.wikimedia.org/wiki/Space_debris

...for some examples. By breaking up the tank, you bring the
probability of anything hitting the ground way down (way down from an
already low probability to begin with, I'll add).
--
Andrew J. Higgins Mechanical Engineering Dept.
Associate Professor McGill University
Shock Wave Physics Group Montreal, Quebec CANADA
http://people.mcgill.ca/andrew.higgins/
Although it's in the nature of things that smaller pieces are more difficult to find, and less easy to recognise for what they are.
It's also in the nature of things that if they are small, their orbits
decay much more rapidly than things tht are large (like the size of
schoo buses).
Depends what orbit they end up in. A piece that gains energy on interceptor impact will be in an orbit that is higher up for most of the time, and therefore not experiencing drag for most of its orbit.

I think that argument also assumes that the densities* of the large object
and the fragments aren't too different. (* More accurately, the masses per
unit (area perpendicular to the direction of motion). )

Certainly the fragments will tend to have lower densities (in the sense you defined) then the original. But it doesn't appear to require a large change in energy (as a proportion of the total kinetic + potential) for the resulting orbit to be mostly outside any significant atmosphere. So although the fragment undergoes greater deceleration during the time it spends near the original altitude, that time will not be great.

Sylvia.
.

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