Light Speed Defenses

Earl Colby Pottinger wrote:
Anthony Frost :

In message
Sander Vesik wrote:

Keith F. Lynch wrote:

By the time it's noticed that a ship is approaching earth at 90% the
speed of light, it's far too late to do anything about it. And when
it hits, it will devastate a continent.

You need an early warning system that will spot any such 1-2 light
minutes
out and then you shoot a stream of protons at 99.9999+% of lightspeed at

it and watch it blow up.

And hope it takes less than 12 seconds to get the cannon aimed and
firing. Much, much less than 12 seconds in fact because, even if you've
managed to destroy it, you've still got a cloud of lumpy plasma heading
for you at nearly 90% of lightspeed which isn't going to do your
atmosphere any good.

You seemed to make very limited range for detection. If the SS is detected
one light year out then you have just over a months warning. If you fire
soon after that warning you show intercept the SS about 15-18 light days out.

That's a moderately dense net.
A light year out, a months warning.

Assuming a tenth of that is light travel time to the sensor, and assuming
it's passive, that's around a thousand detectors.

Then there is the interesting issue of how you detect a non-emitting
body being as stealthy as it can going past a light week away.

How brightly would such a body make interstellar plasma glow?

Earl Colby Pottinger wrote

If the SS is detected one light year out...



One light year seems pretty ambitious, but has anybody
actually done a study of the signatures a large body would
generate moving through the interstellar medium at close
to the speed of light?

"Allen Thomson" kirjoitti viestissä
om...
Earl Colby Pottinger wrote

One light year seems pretty ambitious, but has anybody
actually done a study of the signatures a large body would
generate moving through the interstellar medium at close
to the speed of light?

1987Natur.330..455Y

Abstract
A highly unusual radio source lying within 1 deg of the Galactic center has
been discovered whose 'cometary' morphology suggests that it is a wake
produced by a radio source moving supersonically with respect to the ambient
interstellar medium. Maps of the source are shown, and its characteristics
are discussed. Two possible models which might explain the wake are
suggested.

H Tavaila

"Harri Tavaila" writes:

"Allen Thomson" kirjoitti viestissä
om...

One light year seems pretty ambitious, but has anybody
actually done a study of the signatures a large body would
generate moving through the interstellar medium at close
to the speed of light?

1987Natur.330..455Y

Abstract
A highly unusual radio source lying within 1 deg of the Galactic center
has been discovered whose 'cometary' morphology suggests that it is a
wake produced by a radio source moving supersonically with respect to
the ambient interstellar medium. Maps of the source are shown, and its
characteristics are discussed. Two possible models which might explain
the wake are suggested.

Interesting, but probably not relevant to the question being posed, because
the speed of sound in the interstellar medium is only on the order of the
mean thermal velocity of the interstellar medium's gas molecules, which is
many orders of magnitude less than the speed of light.

It is difficult to predict how relativistic bulk condensed matter would
interact with interstellar gas; however, it is not unreasonable to expect
that a certain amount of X-ray and gamma radiation would be produced when
gas molecules hit a relativistic projectile, and if it had a high enough
gamma-factor, possibly even charged and neutral pions (which would decay
to muons and gammas, respectively, and the muons would decay to electrons
or positrons). Relative to the Earth frame, these produced particles would
be aberrated forward into a cone about its trajectory with an opening angle
~1/(2*\gamma), and doppler-shifted upward to even higher energies.
Hence, an oncoming relativistic projectile _might_ appear as a rapidly
brightening "point" source of beamed high energy gamma radiation, and if
it was moving faster than the pion production threshold, there might also
be a "wake" of annhilation radiation from the pion-decay positrons...


-- Gordon D. Pusch

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