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 03:11:53 GMT
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Viewed:
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786 times
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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.
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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Message has 2 Replies:
 | | Re: Hypothetical design question
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| (...) Yeah, one would hope that if we ever achieve the capability of moving that fast, we'd also have the capability of dealing with associated problems. And if it's comparable to a sports car's engine, I'd think heat buildup would be a bit of a (...) (21 years ago, 24-Jun-03, to lugnet.space, FTX)
| | | Re: Hypothetical design question
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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 (...) (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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| (...) That's essentially correct. Two cars hitting each other head-on at 30MPH is effectively the same as one car hitting a stationary vehicle at 60MPH. Obviously the two accidents would not be perfect mirror images of each other, but the level of (...) (21 years ago, 23-Jun-03, to lugnet.space, FTX)
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