[meteorite-list] U.S. To Shoot Down Defunct Spy Satellite

[Sterling K. Webb]

Hi,

    One news report says that a Pentagon spokesperson has said
that USA-193 will be taken out by an "SM-3" missile, and several
news reports have made mention of a U.S. Navy cruiser as the
platform for the USA-193 takedown.

    A thorough rundown of the RIM-161 SM-3 Aegis Ballistic
Missile Defense system can be found at the following webpage:
http://www.globalsecurity.org/space/systems/sm3.htm

    The Aegis SM-3 is designed as a defense against short- and
intermediate-range ballistic missiles. It uses long-wave infrared
sensors with a range of 300 km. The KW (Kinetic Warhead) is
a self-contained unit with its own solid rocket engines, its own
control and guidance system, and its own brain, which is "smart"
enough to discriminate between true targets and decoys, radar-
confusing shapes and other defensive measures.

    Since USA-193 has no defenses nor ability to maneuver, it can
safely be considered a sitting duck, I think, and not a match for
the SM-3:
    "Discrimination algorithms enable defense systems to compare
objects in a target scene to determine which to intercept. Increasingly
complex threats with separated target elements, countermeasures,
and debris, require advanced signal processing and discrimination
algorithms to identify object features needed to provide robust target
selection. SM-3 has flown and demonstrated fundamental discrimination
capability for unitary threats."

    USA-193 should be a goner. Compared to the "usual" target for an
SM-3, it's lower, less deceptive, less defended, unshielded, uncloaked,
too warm (infra-red, remember?) -- however, it is faster than a shorter-
range ballistic missile would be.

    Will the SM-3 pass the "eBay test"? That is, no surviving pieces
make it to Earth that are big enough to sell on eBay? We'll know in
a few weeks.


Sterling K. Webb
----------------------------------------------------------------------
----- Original Message ----- 
From: "Matson, Robert D." <ROBERT.D.MATSON at saic.com>
To: "Chris Peterson" <clp at alumni.caltech.edu>; "Meteorite List" 
<meteorite-list at meteoritecentral.com>
Cc: <sterling_k_webb at sbcglobal.net>
Sent: Thursday, February 14, 2008 12:57 PM
Subject: RE: [meteorite-list] U.S. To Shoot Down Defunct Spy Satellite


Hi Chris,

> I don't think we have any technology capable of "shooting down" a
satellite.
> What I guess they'll do is turn it into a debris cloud ...

A semantic distinction, though I agree it is prone to misinterpretation
by the majority of the general public.  It's not like shooting down a
plane, where all the debris impacts within 20 miles of the intercept.

> ... and the individual components will separately decay and burn up
> over the next few months (or years).

More like hours or days.  This will not be like the Chinese ASAT
test, where the target satellite was at a higher altitude.  USA 193
is within a few weeks of natural reentry; since the orbit has
already been circularized by atmospheric drag, any impulse addition
of energy will result in fragments that have higher eccentricity.
So a large number of those fragments' orbits will have perigees
below 100 km -- in other words, they will decay within one orbit.

The only fragments that may end up with lifetimes slightly longer
than an unintercepted USA 193 are those which depart the impact
point with higher velocity _and_ in directions very close to the
plane that is perpendicular to the satellite radius vector at
impact.  Sorry for the awkward description -- a picture would
explain this much better.  Another way of stating this is that
to survive longer, a fragment's post-impact orbit must have
its perihelion close to the impact location.  Only a tiny
fraction of the fragments will end up this way.  And keep in
mind that these few fragments will still have perihelions lower
than USA 193's altitude at impact, which means they won't last
long.

Feel free to forward to the met-list... --Rob