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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Mon, 23 Jun 2003 17:08:44 GMT
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Viewed:
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505 times
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In lugnet.space, Sylvia Tresto wrote:
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In lugnet.space, George Haberberger wrote:
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-snip-
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So, for a near light speed craft, anything hitting it would probably destroy
it, if it didn’t have some sort of shield. I can’t find the link, but there
is a page that describes very nicely what happens when an object the size of
a soup can hits a Star Destroyer at half the speed of light ( a huge
explosion).
Thanks,
George
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No thank YOU, George, for clearing some things up.
What about this, taken from the SF novel Revelation Space by Alistair
Reynolds, it made me wonder wether or not I should make my new ship look like
a needle: “Space only approximated a vacuum at slow speeds. Up near lightspeed
- which was where these ships spent most of their time - it was like cutting
through a howling gale of atmosphere. That was why they looked like daggers:
conic hull tapering to a needle-sharp prow to punch the interstellar medium.”
Is this a non-sensical design (from the point of view of physics and not
esthetics)?
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Sylvi,
This is an interesting reference. I can only guess at Reynolds’ inspiration,
though it does sound like an extrapolation of designs based on hypersonic flow
theory (on that front, see
http://www.aerospaceweb.org/design/waverider/waverider.shtml -- note how the
optimal shape changes as the design Mach number increases).
As for relativistic speeds, it may not be completely crazy to minimize frontal
area, though ‘drag reduction’ wouldn’t seem to be the biggest problem (by the
following back-of-the-envelope physics, anyhow)...
The density of normal matter in the interstellar vacuum is sufficiently low by
some estimates (something like 1 hydrogen atom per cubic meter of space?) that
drag wouldn’t seem to be much of an issue. Converting the mass of one hydrogen
atom into energy using E=mc^2, you get something like 1.5E-10 watt, seemingly an
upper bound on the energy transfer. This is so small that even colliding with
hundreds of millions per second per square meter of frontal area wouldn’t lead
to much of an energy dissipation issue.
However, the bombardment of particles over time could adversely affect material
properties (e.g., bombardment by the nonrelativistic solar wind embeds enough
hydrogen in the lunar crust to make people think of refining moon rock as a
method for obtaining useful amounts of rocket fuel) such that you might want to
avoid it for other reasons.
Certainly, George makes an excellent point that the effects of collisions with
small objects (but orders of magnitude larger than individual atoms) at
relativistic speeds could easily release disastrous amounts of energy.
Minimizing frontal area, other things equal, would seem to help reduce the
probability of such collisions. It may also simplify the design of a
navigational deflector. But I’d definitely want a deflector if it were my ship!
Regards, Tom
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Message has 1 Reply:
 | | Re: Hypothetical design question
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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. Not (...) (21 years ago, 23-Jun-03, to lugnet.space, FTX)
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Message is in Reply To:
| | Re: Hypothetical design question
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| (...) Wow, that's quite a bit more complicated than I assumed... (...) Yup, I had those in mind for vehicles which actually travel through atmosphere. (...) No thank YOU, George, for clearing some things up. What about this, taken from the SF novel (...) (21 years ago, 23-Jun-03, to lugnet.space)
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