Subject:
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Re: Some great Space info and dicussion
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Newsgroups:
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lugnet.space
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Date:
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Wed, 22 Jan 2003 09:14:35 GMT
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Viewed:
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999 times
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In lugnet.space, Jordan D. Greer writes:
> Ahh, but that assumes you have the technology. His theory is that you
> > will get blasted to oblivion before you get the technology. There's • also
> > the time factor. You don't have all that blasted much time to react to
> > something approaching at relativistic speeds (remember, if it's
> > approaching at 90% the speed of light, you only have 10% of the time it
> > takes for the object to reach you). Another part of his idea was that
> > perhaps SETI isn't such a good idea: "Hey fellas, we're a nascent
> > technological civilization, come blast us to oblivion before we learn
> > anything dangerous."
>
> Unless acceleration is almost instantaneous, the waste energy of
> whatever accelerates the rock to light speed will reach you long before
> the rock does.
That too requires the target civilization to recognize
it (the energy wastage) for what it is. If there *is*
wastage to detect in the direction of the target--again,
not something we can be sure of, necessarily; it may be
that one has to be, say, 0.05 degrees off the ordinal
"target direction" before they're in the cone of detection
for such energy (because the rock absorbs the rest, of
course!), and on an interstellar scale, that may be enough
to require you be past your heliopause for detection.
> Assuming that the rock's rest mass is 1000 tonnes, accelerating it to
> 90% of light speed would require 2.0647*10^23 joules of energy. This is
> an energy release 4.9324*10^7 times the 50 megaton Tsar Bomba, the
> largest nuclear weapon ever detonated by humans.
This is why .9c always seems to be a bit ridiculous for
this or any similar undertaking. Why not .75c? Or less?
Does anyone remember how fast Heinlein suggested his
rocks o' death were going in _Starship Troopers_?
> Don't tell me that an energy release of this magnitude would not be
> noticed by the opposing side. If you're going to generate that much
> energy, you might as well directly apply it to the target to avoid
> wasteful expenditure of resources.
Except that it's possible, if the ICM has certain
properties, that a relativistic rock may in fact do
better at transmitting that energy than a direct
application of energy towards the target. It seems
crude, but since we've never actually sent an object
into the ICM (and we won't get any data back from
the ones that are getting there now) it's hard to
say.
The rock does, of course, have the benefit of
looking vaguely like it wasn't intentional. That
way, if they survive, or if you miss, you're not
totally exposed. (This is of course moot if you
shoot it at .9c or even much above .1c; that's
pretty darn deliberate, unless there's something
out there with momentum-conservation properties
that are truly bizarre.)
> Note that the figures above only
> display the energy required to accelerate the rock to 90% light speed.
> Due to inefficiencies, a power source capable of generating within the
> necessary time much more energy than is required to accelerate the rock,
> meaning several orders of magnitude, would be required.
> Let's not even get into the necessary capabilities of the heat
> dissipation system.
That's a much more serious problem for the shooter,
IMHO.
> On the other hand, knocking rocks into a planet is a much simpler
> proposition. One only has to reduce the kinetic energy of a rock
> orbiting the target to less than that of the rock's gravitational
> binding energy.
> If you need to kill a planet, sending into the target's gravity well a
> rock of huge mass will require much less technological capabilities than
> accelerating a rock to relativistic velocities.
However, it also requires much less in the way of technical
capability to stop. It also suggests that you need to get
there--or at least get close to there--to do it. At that
point, why not just Tsar Bomba them? Is maintaining a veneer
of "natural force of destruction" really that important at
that point?
(And why am I hearing Ritchie Valens all of a sudden?)
best
LFB
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Message is in Reply To:
 | | Re: Some great Space info and dicussion
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| Ahh, but that assumes you have the technology. His theory is that you (...) also (...) Unless acceleration is almost instantaneous, the waste energy of whatever accelerates the rock to light speed will reach you long before the rock does. Assuming (...) (22 years ago, 21-Jan-03, to lugnet.space)
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