From: jdnicoll@prism.ccs.uwo.ca (James Davis Nicoll)
Subject: Re: Wreaking a habitat (was Re: Wrecking a Planet
Organization: University of Western Ontario, London
Date: Sat, 9 Jan 1993 20:09:29 GMT


In article <rwallace.726539394@unix1.tcd.ie> rwallace@unix1.tcd.ie (russell wallace) writes:
>In <1993Jan8.181818.25839@julian.uwo.ca> jdnicoll@prism.ccs.uwo.ca (James Davis Nicoll) writes:
>
>
>>	I find it hard to believe in habitats which are 10**9 tonnes
>>*and* able to jink around in wartime *and* able to function as a viable
>>commercial/industrial entity. If our target uses high Isp drives, then
>>they will have to radiate a hell of a lot of heat while swooping around.
>>If they use low Isp drives, then the mass-ratios involved will limit
>
>Who said anything about jinking around? The habitat can have a very low
>acceleration, because it does not have to dodge missiles etc. at close
>range but only to move enough that you can't hit it with ballistic
>projectiles from extreme range, like you can a planet.

	0.01  m/s**2  isn't  exactly  a  huge acceleration, and
it causes  immense heat problems,as  shown  below.

>>delta-vee.  Radiator size is governed by the temperature the radiator  
>>operates at, and the quantity of heat that needs to be dumped. I think
>>the habitat is going to present a hot target. For a 10**9 t hab, with
>>a 200 km/s ion drive, able to convert electricity into Ek of reaction
>>mass at 60% efficiency, accelerating at .01 m/s**2, I get ~7x10**14 W
>>that need getting rid of. If our habitat is about the density of
>>water, and cylindrical, with a 1000 m radius and 320 m length, that's
>>a surface area of ~3.5x10**6 m**2 to radiate from: if we're  talking
>>black body radiation, that's a temperature of about 7,700 K if I haven't
>
>The habitat is going to be a lot less dense than water, because the
>interior is hollow.

	Fine. Make the  habitat  1/1000  as dense  as   water: the
relevent equation is  E = aT**4, where E is power-per-unit-area,
a is the Stephan-Boltzmann Constant, and  T is temperature.  Dropping
E by a factor of 100 only drops T  by ~3.2 to 2400  K.

>>screwed up: physics people feel free to check this, as  my schooling is
>>in poly-sci/econ. I can't help  but  suspect that having a surface 
>>temperature comparable to a star might place large and difficult to
>>achieve demands on the habitat's life support systems. If the habitat
>>uses 4000 K radiators, they should be about 5x10**7 m**2, which should
>>give missiles a nice large hot target to aim at.
>
>Sure, but it doesn't matter if you make a few small holes in the
>radiator, which are easily repaired, and again you have to use missiles
>rather than bombs or rocks, which makes the operation unreasonably
>expensive.

	I can  think  of at least  one way to  couple  the energy
from an  atomic weapon to a target  in space,   inspired by how
Orion worked. What I  have  in
>
>>	.01 m/s**2 lets the hab change its position by ~65 km given
>>an hour's warning. Of course, actively tracking dirigible torpedos might
>>well out-do the hab  wrt both acceleration and delta-vee...
>
>Sure. See my above comment.
>
>--
>"To summarize the summary of the summary: people are a problem"
>Russell Wallace, Trinity College, Dublin
>rwallace@unix1.tcd.ie


From fass@math.uwaterloo.ca Sat Jan  9 13:01:48 1993
Received: from math.uwaterloo.ca by engrg.uwo.ca;
	(id AA04475) Sat, 9 Jan 93 13:01:39 EST
Received: by math.uwaterloo.ca
	id <AA28683>; Sat, 9 Jan 93 13:01:28 -0500
Date: Sat, 9 Jan 93 13:01:28 -0500
From: The FASS Theatre Company <fass@math.uwaterloo.ca>
Message-Id: <9301091801.AA28683@math.uwaterloo.ca>
To: jdnicoll@engrg.uwo.ca
Subject: habf
Status: R



In article <rwallace.726539394@unix1.tcd.ie> rwallace@unix1.tcd.ie (russell wallace) writes:
>In <1993Jan8.181818.25839@julian.uwo.ca> jdnicoll@prism.ccs.uwo.ca (James Davis Nicoll) writes:
>
>>	I find it hard to believe in habitats which are 10**9 tonnes
>>*and* able to jink around in wartime *and* able to function as a viable
>>commercial/industrial entity. If our target uses high Isp drives, then
>>they will have to radiate a hell of a lot of heat while swooping around.
>>If they use low Isp drives, then the mass-ratios involved will limit
>
>Who said anything about jinking around? The habitat can have a very low
>acceleration, because it does not have to dodge missiles etc. at close
>range but only to move enough that you can't hit it with ballistic
>projectiles from extreme range, like you can a planet.

	0.01  m/s**2  isn't  exactly  a  huge acceleration, and
it causes  immense heat problems,as  shown  below.

>>delta-vee.  Radiator size is governed by the temperature the radiator  
>>operates at, and the quantity of heat that needs to be dumped. I think
>>the habitat is going to present a hot target. For a 10**9 t hab, with
>>a 200 km/s ion drive, able to convert electricity into Ek of reaction
>>mass at 60% efficiency, accelerating at .01 m/s**2, I get ~7x10**14 W
>>that need getting rid of. If our habitat is about the density of
>>water, and cylindrical, with a 1000 m radius and 320 m length, that's
>>a surface area of ~3.5x10**6 m**2 to radiate from: if we're  talking
>>black body radiation, that's a temperature of about 7,700 K if I haven't
>
>The habitat is going to be a lot less dense than water, because the
>interior is hollow.

	Fine. Make the  habitat  1/1000  as dense  as   water: the
relevent equation is  E = aT**4, where E is power-per-unit-area,
a is the Stephan-Boltzmann Constant, and  T is temperature.  Dropping
E by a factor of 100 only drops T  by ~3.2 to 2400  K.

>>screwed up: physics people feel free to check this, as  my schooling is
>>in poly-sci/econ. I can't help  but  suspect that having a surface 
>>temperature comparable to a star might place large and difficult to
>>achieve demands on the habitat's life support systems. If the habitat
>>uses 4000 K radiators, they should be about 5x10**7 m**2, which should
>>give missiles a nice large hot target to aim at.
>
>Sure, but it doesn't matter if you make a few small holes in the
>radiator, which are easily repaired, and again you have to use missiles
>rather than bombs or rocks, which makes the operation unreasonably
>expensive.

	I can  think  of at least  one way to  couple  the energy
from an  atomic weapon to a target  in space,   inspired by how
Orion worked. What I  have  in mind wasn't 'a few holes' but enough
damage to destroy the radiators. I fail to see why people in space
will find themselves limited to WW II technology (Uncontrolled
missiles without terminal guidance systems). If smart weapons are
purchased by 1990 nations, why should that  technology be too
expensive for a culture  that can build 10**9 t habitats? Making
a missile with tracking and propulsive ability  is already an
exploited technology, and  I  expect that if technology that enables
a 10**9 t hab to accelerate itself should be applicable to missiles
as well.

>>	.01 m/s**2 lets the hab change its position by ~65 km given
>>an hour's warning. Of course, actively tracking dirigible torpedos might
>>well out-do the hab  wrt both acceleration and delta-vee...
>
>Sure. See my above comment.

	And see mine. Habitats  are indeed hard to destroy, as long
as the builders  use  21st Century technology  and  the attackers  
refrain from using post-1945 technology. I doubt  those constraints
will  be met.

							James  Nicoll

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