Subject:
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Re: Hypothetical design question
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Newsgroups:
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lugnet.space
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Date:
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Tue, 24 Jun 2003 10:05:08 GMT
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Viewed:
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683 times
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In lugnet.space, Tom Bozzo wrote:
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In lugnet.space, David Laswell wrote:
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In lugnet.space, Jonathan Mizner wrote:
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If I understand physics correctly, it doesn’t make a difference whether it
is the ship traveling at .9 c or the hydrogen atom. The energy released is
the same.
Thus, that atom is effectively dealing far, far more energy than 1.5E-10
watts.
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How do you figure? It’s the smaller mass that determines the total energy
generated by impact, not the larger mass. A single hydrogen molecule
traveling at .9c does not cause more damage to a Star Destroyer than it
would to an X-Wing just because the ISD is bigger.
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You’re right, though I read Jonathan’s point as being that I didn’t account
for relativistic effects in the energy calculation, which is true. If I have
the math right, the crossover point where the relativistic energy exceeds the
rest mass times c-squared is something like 0.3c. However, the difference is
still only a factor of 10 or so at 0.95c.
Cf. http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/relmom.html#c4
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One individual hydrogen molecule will not cause much drag on anything large
enough to fit a human inside, but hitting a whole mess of them (like
travelling through a nebula) will result in accumulation of drag. It’s
kinda like hitting a brick wall one brick at a time. Without any means of
increasing your speed, it will eventually bring you to a standstill.
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Density does indeed matter -- and there I was off by a good bit (a NASA
Goddard page gives 1 atom per cc as the density of the interstellar medium),
though the drag/energy dissipation problem still seems manageable until you
get to very high relativistic speeds. For instance, it’s only a few hundred
kW per square meter of frontal area at 0.95c and the 1 atom/cc density --
comparable to the peak output of a fast car’s engine. Nothing, really, if
you can accelerate a spaceship to 0.95c in the first place.
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But you’re going at .95c, which means you’re hitting lots of particles per
second. If your ship has a frontal area of 9 sq meters, and 90000 square
centimeters, that’s 90,000 molecules you’re running into for every centimeter
forward in space you travel. At .95c, one is traveling quite a few centimeters
forward per second. Heat would accumulate enormously fast, almost instantly
fast at such a speed, and would probably fatal to the craft.
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Back on the topic of building, I think the nature of the medium would make it
a challenge to to build, with real bricks, an interesting-looking and
stucturally sound model of one of those needle-shaped relativistic starships,
the underlying science or lack thereof notwithstanding. A much-extended
version of Bruce Lowell’s “Starflux” comes to mind for starters.
Tom
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The main problem is making the edges, I’d say. Although someone did make a
highly impressive A-wing-like racer on brickshelf a while back (using a few
clone parts, but quite forgivable in the circumstances) using all-tiled surfaces
with many angles.
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Message has 1 Reply:
 | | Re: Hypothetical design question
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| (...) Jonathan, The craft would indeed contact a lot of particles (about 2.85x10^14 per second per square meter of frontal area at 0.95c) but the energy per particle is very small. So the total energy of those particles seems manageable in (...) (21 years ago, 24-Jun-03, to lugnet.space, FTX)
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Message is in Reply To:
| | Re: Hypothetical design question
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| (...) You're right, though I read Jonathan's point as being that I didn't account for relativistic effects in the energy calculation, which is true. If I have the math right, the crossover point where the relativistic energy exceeds the rest mass (...) (21 years ago, 24-Jun-03, to lugnet.space, FTX)
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