![[F]](../_images/site.gif) New York Times on the Web Forums  Science
Technology has always found its greatest consumer in a nation's
war and defense efforts. Since the last attempts at a "Star Wars"
defense system, has technology changed considerably enough to make
the latest Missile Defense initiatives more successful? Can such an
application of science be successful? Is a militarized space
inevitable, necessary or impossible?
    (10706 previous messages)
rshow55
- 04:45pm Jan 9, 2002 EST (#10707
of 10716) 
You want to give me numbers of the "kinetic energy of the photon"
effect? I think it is a preposterous idea, but I've been wrong
before. Don't think I am this time.
You can measure "light pressure" - and it is real - but it is a
small effect.
rshow55
- 04:46pm Jan 9, 2002 EST (#10708
of 10716)
And reflected light exerts the same pressure as absorbed?
rshow55
- 04:47pm Jan 9, 2002 EST (#10709
of 10716)
So far, you're not disputing that relective coatings (including
reflective coatings well tuned to the COIL lasar wavelength) can be
made in decal form. I think you're right not to do so.
rshow55
- 04:50pm Jan 9, 2002 EST (#10710
of 10716)
Here are some standard things about light absorbtion,
transmission, and reflection.
Light radiation hitting (or passing through) a piece of material
can be absorbed, reflected, transmitted, or all three, with the
total of the three equalling the incident energy. The radiation
energy conservation law is
a + r + t = 1
where a is absorption, r is reflection and t
is transmission.
let's consider a case where ... t = 0 .... for the piece
of the material we're considering in our particular, geometrically
defined "system."
The thermal emissivity factor e of the surface at a
wavelength with respect to black body radiation at that wavelength
is also of interest. e = a . The emissivity factor of
thermal radiation at a particular wavelength is the same as
absorbtion factor for that wavelength.
e = a = (1 - r)
Another important thing about mirror surfaces is that "angle of
incidence = angle of reflection" .
These things apply to missile defense circumstances.
rshow55
- 04:52pm Jan 9, 2002 EST (#10711
of 10716)
With a clean refective decal with a mirror surface, a warhead
(or decoy) will be very much harder to see from its own thermal
radiation, or from light illumination from a lasar. And harder to
destroy.
If r = .999 , the thermal emissivity is only 1/1000 the
intensity of black body radiation.
If r = .999 for lasar wavelength light, only 1/1000 of the
incident enegy targeted onto the surface is absorbed.
If the surface is a good mirror, it may completely
eliminate return radiation to a detector from an illuminating lasar,
because the light will be reflected in other directions.
* * * * * *
For a missile body on boost phase, r may be much lower,
and a higher.
* * * * * * *
But the simple physical relations of absorbtion, reflection, and
mirror function apply - (when they can be simply applied. )
rshow55
- 04:55pm Jan 9, 2002 EST (#10712
of 10716)
If these things are considered (and I don't believe they have
been) they make marginal or already far-fetched missile
defense programs (including the one that is subject of the Coyle
report) even more marginal and even more far-fetched.
mazza9
- 05:15pm Jan 9, 2002 EST (#10713
of 10716)
Louis Mazza
Solar wind lowers the orbit of satellites and if not reboost,(as
the ISS is each time the shuttle docks)it deorbits. A laser with
megajoules of punch will crush the target. I saw the picture and the
Titan cylindrical body was crushed like a beer can by the force of
the strike!
LouMazza
rshow55
- 05:26pm Jan 9, 2002 EST (#10714
of 10716)
Mazza, you amaze me. Could you perchance find a reference from
DOD or anybody else respectable in the last few years that speaks of
"light pressure" as a mechanism for killing a target with a lasar?
I've read a certain amount about the COIL system, and "light
pressure" isn't mentioned, that I recall.
You aren't, so far, disputing the simple engineering-physics I
set out, about absorbtion and reflection? Do you wish to do so?
rshow55
- 05:32pm Jan 9, 2002 EST (#10715
of 10716)
You aren't disputing the issues that connect to detection (of
thermal radiation from the source, or of illuminated radiation) are
you?
High reflectivity means low emissivity.
Angle of incidence = angle of reflection for a smooth
mirror.
No?
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