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Message no. 1
From: Michael Orion Jackson <orion@****.CC.UTEXAS.EDU>
Subject: [vaguely OT] solar sails
Date: Tue, 25 Aug 1998 07:07:57 -0500
You wouldn't need on-board lasers. To generate enough light
pressure would require an immense laser battery and quite probably a
fusion power plant or some other big power source to power the lasers.
For in-system travel, the sun should be enough. Admittedly, acceleration
would be painfully slow and handling would be like a drunken cow, but
you do save quite a bit on your spacecraft if you don't have to haul about
mass for fuel and engine (leaving space for lots of cargo). I don't see
solar sails being practical for human-occupied spacecraft due to their
long travel times, but they'd be perfect for automated cargo ships
out bound.
Another interesting idea is a magnetic sail. Basically a big wire
loop or loops carrying current, the magnetic flux from the star in the
system would push on it generating thrust. You could even reverse and
come back inwards by reversing the current flow through the loops. (I
envision the craft at the center of a spider web looking concentric ring
of cables. If the cables super conducted that'd be all the better. A
rigid framework would allow the craft to reverse thrust without snarling
lines, and if the loops were independent on each side or if they ran in
loops like slices of a pizza they could be switched in different current
directions to maneuver the craft pretty well.)

*****************Michael Orion Jackson******************
***********TAMS Class of 96/UT Class of 2000************
*********************Random Quote:**********************
*"Out! Out! Out you demons of stupidity!":Dogbert/me****
********************************************************
Message no. 2
From: Adam Getchell <acgetchell@*******.EDU>
Subject: Re: [vaguely OT] solar sails
Date: Tue, 25 Aug 1998 10:18:32 -0700
> You wouldn't need on-board lasers. To generate enough light
>pressure would require an immense laser battery and quite probably a
>fusion power plant or some other big power source to power the lasers.

Who said anything about on-board lasers? Solar powered lasers hung out
around Mercury would be best.

You should look at Robert L. Forward's "Rocheworld" series. They use a
lightsail craft to get to Barnard's star. The upshot of it is it takes
about 40 years for a 3000 ton craft and requires a lightsail 1000 km in
diameter, powered by a series of terawatt lasers around Mercury. The sun's
pressure would not be enough.

Interestingly, by tacking against the sun and using angular orbital
momentum (more increases orbit, less decreases) you can go towards or away
from the sun while the solar sail is facing it.

>For in-system travel, the sun should be enough. Admittedly, acceleration
>would be painfully slow and handling would be like a drunken cow, but
>you do save quite a bit on your spacecraft if you don't have to haul about
>mass for fuel and engine (leaving space for lots of cargo). I don't see
>solar sails being practical for human-occupied spacecraft due to their
>long travel times, but they'd be perfect for automated cargo ships
>out bound.

>envision the craft at the center of a spider web looking concentric ring
>of cables. If the cables super conducted that'd be all the better. A

Superconducting cables would be no problem. Ambient temperature is 3K, well
below the range for almost all superconductors.

>*****************Michael Orion Jackson******************
>***********TAMS Class of 96/UT Class of 2000************
>*********************Random Quote:**********************
>*"Out! Out! Out you demons of stupidity!":Dogbert/me****
>********************************************************

--Adam

acgetchell@*******.edu
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu
Message no. 3
From: K is the Symbol <Ereskanti@***.COM>
Subject: Re: [vaguely OT] solar sails
Date: Tue, 25 Aug 1998 14:33:12 EDT
In a message dated 8/25/1998 7:08:47 AM US Eastern Standard Time,
orion@****.CC.UTEXAS.EDU writes:

> Another interesting idea is a magnetic sail. Basically a big wire
> loop or loops carrying current, the magnetic flux from the star in the
> system would push on it generating thrust. You could even reverse and
> come back inwards by reversing the current flow through the loops. (I
> envision the craft at the center of a spider web looking concentric ring
> of cables. If the cables super conducted that'd be all the better. A
> rigid framework would allow the craft to reverse thrust without snarling
> lines, and if the loops were independent on each side or if they ran in
> loops like slices of a pizza they could be switched in different current
> directions to maneuver the craft pretty well.)
>
Michael, I have to give you credit, I hadn't really put much thought into
this, but it does open up to some possibilities. The concepts are also very
interesting as far as "changing directions" or "guidance" would be
concerned.
Very "SciFi" if you get my meaning. May have to look into this one.

-K
Message no. 4
From: K is the Symbol <Ereskanti@***.COM>
Subject: Re: [vaguely OT] solar sails
Date: Tue, 25 Aug 1998 15:24:17 EDT
In a message dated 8/25/1998 12:18:03 PM US Eastern Standard Time,
acgetchell@*******.EDU writes:

>
> Superconducting cables would be no problem. Ambient temperature is 3K, well
> below the range for almost all superconductors.
>
Whoa, hold on a second. There is a problem here with thermodynamics of
material in space. Yes, in "Free Space", the temperature is as you describe,
incredibly low. But the instant you give the traversing energy something to
land/impact upon, the temperature skyrockets to well above boiling
temperatures without any difficulty.

-K
Message no. 5
From: Adam Getchell <acgetchell@*******.EDU>
Subject: Re: [vaguely OT] solar sails
Date: Tue, 25 Aug 1998 14:13:29 -0700
>In a message dated 8/25/1998 12:18:03 PM US Eastern Standard Time,
>acgetchell@*******.EDU writes:
>Whoa, hold on a second. There is a problem here with thermodynamics of
>material in space. Yes, in "Free Space", the temperature is as you
describe,
>incredibly low. But the instant you give the traversing energy something to
>land/impact upon, the temperature skyrockets to well above boiling
>temperatures without any difficulty.

What are you talking about?

If you are referring to Ohmic heating of the cable, Bzzzt!, you are
incorrect. Ohmic heating requires resistance ... that's the point of a
superconductor.

Go back and check the definition of the word "Thermodynamics". I do not
think it means what you think it means ...

"Give the traversing energy something to land/impact upon"? You're going to
have to be more precise than that, that statement doesn't mean anything in
physics.

>-K

--Adam

acgetchell@*******.edu
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu
Message no. 6
From: The Bookworm <Thomas.M.Price@*******.EDU>
Subject: Re: [vaguely OT] solar sails
Date: Tue, 25 Aug 1998 19:30:33 -0500
On Tue, 25 Aug 1998, Adam Getchell wrote:

> "Give the traversing energy something to land/impact upon"? You're going to
> have to be more precise than that, that statement doesn't mean anything in
> physics.

HMM since i was saying that a superconductive cable could not use
use the background temp of space as the only means of cooling it to
operating Temp i think i know what he ment. When you put something out in
space it gets in the way of the solar energy streaming out in the form of
radiation and pataticle streams from the sun. While it is true that an
object in shade will be REALLY cold due to being able to radiate to a
3kelvin background temp the object in sunlight will be heating up like
crazy. A modern space suit has a lot more COOLING equiptment in it than
it has heating equiptment. Your body is good at gerating its own heat(its
a waste product of a lot of biochemical reactions) but without an
atmosphere to evaporate sweat into your body is really bad at cooling
itself off even whithout the solar heating problem. So basicaly you
might have to either cool the superconducting cables when in the inner
solar system or use some sort of shading to keep the cables out of the
solar radiation.

Thomas Price
AKA The Bookworm
thomas.m.price@*******.edu
Message no. 7
From: Robert Watkins <robert.watkins@******.COM>
Subject: Re: [vaguely OT] solar sails
Date: Wed, 26 Aug 1998 10:44:04 +1000
> HMM since i was saying that a superconductive cable could not use
> use the background temp of space as the only means of cooling it to
> operating Temp i think i know what he ment. When you put something out in
> space it gets in the way of the solar energy streaming out in the form of
> radiation and pataticle streams from the sun. While it is true that an
> object in shade will be REALLY cold due to being able to radiate to a
> 3kelvin background temp the object in sunlight will be heating up like
> crazy. A modern space suit has a lot more COOLING equiptment in it than
> it has heating equiptment. Your body is good at gerating its own heat(its
> a waste product of a lot of biochemical reactions) but without an
> atmosphere to evaporate sweat into your body is really bad at cooling
> itself off even whithout the solar heating problem. So basicaly you
> might have to either cool the superconducting cables when in the inner
> solar system or use some sort of shading to keep the cables out of the
> solar radiation.

How about running the cable through a few tonnes of ice? If you wanted, you
could even put the ice in a reflective tank, to trap the steam, which you
can use for propulsion later. (Or run the steam through a large cooling fin,
to cool it into water again).

Admittedly, you'd want a superconductor which works in the ~0C range, but
you could always use liquid hydrogen or oxygen instead...


--
.sig deleted to conserve electrons. robert.watkins@******.com
Message no. 8
From: K is the Symbol <Ereskanti@***.COM>
Subject: Re: [vaguely OT] solar sails
Date: Wed, 26 Aug 1998 03:24:17 EDT
In a message dated 8/25/1998 4:14:10 PM US Eastern Standard Time,
acgetchell@*******.EDU writes:

>
> What are you talking about?
>
I'll snip the rest.

Let's try this route of explanation then.

If an object is in "view" of the sun, it's surface will superheat in the
environs of space to temperatures well in excess that of boiling unless they
are protected. You mentioned (I think it was you, all this posting/snipping
get's me once in a while ;P) that the temperature of space was around 3K or
so. But that is the "unexposed" temperatures, where there is no solar or
ambient radiation to come in contact with.

Do you follow me now? Where am I getting lost here?

-K
Message no. 9
From: Michael Orion Jackson <orion@****.CC.UTEXAS.EDU>
Subject: Re: [vaguely OT] solar sails
Date: Wed, 26 Aug 1998 06:56:35 -0500
The original idea I remember reading _several_ years ago in
Analog, a scifi mag that blends in fact articles occasionally (speculative
or current, but always pretty well done). The article talked of using a
wire loop carrying current and being able to reverse thrust. (Of course,
I was in like 5th grade at the time, so not having taken electromagnetic
physics I didn't realize this derived from the Right-handed Rule ("Hey
professor! Watch _this_ right-handed action!"<---crude PHY 316 joke).)
The idea that superconducting wire would improve efficiency and using
discrete loops of wire independently switchable for guidance are my own.
(I realized rigid struts would be neccessry too otherwise everythiing
would just flop around into a horrid mess, I think.)
As far as 3k being the ambient temperature, um, are you sure
(whoever said that)? I thought there was temperature in space just like
here, ie due to solar radiation? (Now of course if you are in shadow
things get chilly.) Not working for NASA, I don't know these things...;)
Hey, I hadn't thought of that, maybe I could just call them and ask, it
would be instate long distance... Now if 3k were the ambient temperature
that would be great. Hell, I think everything superconducts at a
temperature that low (most of the metals anyway). Superconductors have
always been sort of a fascination of mine. I haven't reached the level
yet where I can actually research them in a lab or take a class on them,
so I'm stuck reading journals...

*****************Michael Orion Jackson******************
***********TAMS Class of 96/UT Class of 2000************
*********************Random Quote:**********************
*"Why me?" "Because you are in Natural Sciences,silly."*
********************************************************

On Tue, 25 Aug 1998, K is the Symbol wrote:

> In a message dated 8/25/1998 7:08:47 AM US Eastern Standard Time,
> orion@****.CC.UTEXAS.EDU writes:
>
> > Another interesting idea is a magnetic sail. Basically a big wire
> > loop or loops carrying current, the magnetic flux from the star in the
> > system would push on it generating thrust. You could even reverse and
> > come back inwards by reversing the current flow through the loops. (I
> > envision the craft at the center of a spider web looking concentric ring
> > of cables. If the cables super conducted that'd be all the better. A
> > rigid framework would allow the craft to reverse thrust without snarling
> > lines, and if the loops were independent on each side or if they ran in
> > loops like slices of a pizza they could be switched in different current
> > directions to maneuver the craft pretty well.)
> >
> Michael, I have to give you credit, I hadn't really put much thought into
> this, but it does open up to some possibilities. The concepts are also very
> interesting as far as "changing directions" or "guidance" would
be concerned.
> Very "SciFi" if you get my meaning. May have to look into this one.
>
> -K
>
Message no. 10
From: Adam Getchell <acgetchell@*******.EDU>
Subject: Re: [vaguely OT] solar sails
Date: Wed, 26 Aug 1998 09:49:05 -0700
>Let's try this route of explanation then.
>
>If an object is in "view" of the sun, it's surface will superheat in the
>environs of space to temperatures well in excess that of boiling unless they
>are protected. You mentioned (I think it was you, all this posting/snipping

Ah, that's your rationale. It's wrong though. Here's a simple explanation why:

The solar radiance from the sun arriving on earth is 1.35 x 10^3 W/m^2.

Now, a very thick cable will be 1 cm in diameter: therefore, a 1 meter
segment will have an area of 0.01 m^2. The energy falling on a one meter
segment of cable is therefore 13.5 Watts. A one meter segment of copper
cable will mass about 700 grams; copper has a specific heat of 0.384 J/g C.

Given the above figures, the solar irradiance will produce a temperature
change of 0.05 C per second. Now, this is not considering cooling by
irradiance, which is a function of surface area (wheareas absorbsion is a
function of linear area). But at any rate, from the numbers above one can
see that solar heating of a wire is not going to be a problem. For
significant surface area, yes. For a wire, no.

>-K

--Adam

acgetchell@*******.edu
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu
Message no. 11
From: Steve Collins <einan@*********.NET>
Subject: Re: [vaguely OT] solar sails
Date: Wed, 26 Aug 1998 13:05:51 -0400
> As far as 3k being the ambient temperature, um, are you sure
>(whoever said that)? I thought there was temperature in space just like
>here, ie due to solar radiation? (Now of course if you are in shadow
>things get chilly.)

3 deg Kelvin is the temperature of the cosmic background radiation
leftover from the Big Bang. Space has no temperature, temperature is a
property of matter Space being pretty much a vaccum has none but because
of Solar Radiation objects in space usually end up absorbing more energy
that they can get rid of making them hot.

Steve
Message no. 12
From: David Buehrer <dbuehrer@******.CARL.ORG>
Subject: Re: [vaguely OT] solar sails
Date: Wed, 26 Aug 1998 12:06:04 -0600
/ >Let's try this route of explanation then.
/ >
/ >If an object is in "view" of the sun, it's surface will superheat in the
/ >environs of space to temperatures well in excess that of boiling unless they
/ >are protected. You mentioned (I think it was you, all this posting/snipping
/
/ Ah, that's your rationale. It's wrong though. Here's a simple explanation why:
/
/ The solar radiance from the sun arriving on earth is 1.35 x 10^3 W/m^2.

Okay, this one has strayed way off topic and stayed there for to long.
Please wrap it up or take it to private email.

Thank you.

Have fun,
Play nice,
-David, your friendly neighborhood GridSec Assistant :)
--
dbuehrer@******.carl.org, ShadowRN GridSec: Nice Guy Division
The ShadowRN FAQ: http://coastnet.com/~dvixen/srnintro.html
Other GridSec members: Gurth <gurth@******.nl>
Dvixen <dvixen@********.com>
Tim Kerby <drekhead@***.net>
List Administrator: Adam Jury <fro@***.ab.ca>
Message no. 13
From: Tarek Okail <Tarek_Okail@**********.COM>
Subject: Re: [vaguely OT] solar sails
Date: Wed, 26 Aug 1998 17:38:09 -0400
David--

>/ Ah, that's your rationale. It's wrong though. Here's a simple
>/explanation why:
>/
>/ The solar radiance from the sun arriving on earth is 1.35 x 10^3 W/m^2=
.
>
>Okay, this one has strayed way off topic and stayed there for to long.
>Please wrap it up or take it to private email.
>
>Thank you.

Noooo! I found this thread absolutely facinating. Please, please,=

don't make it go away!

Shadowmage
Message no. 14
From: David Buehrer <dbuehrer@******.CARL.ORG>
Subject: Re: [vaguely OT] solar sails
Date: Wed, 26 Aug 1998 20:52:29 -0600
Tarek Okail wrote:
/
/ David--
/
/ >/ Ah, that's your rationale. It's wrong though. Here's a simple
/ >/explanation why:
/ >/
/ >/ The solar radiance from the sun arriving on earth is 1.35 x 10^3 W/m^2=
/ .
/ >
/ >Okay, this one has strayed way off topic and stayed there for to long.
/ >Please wrap it up or take it to private email.
/ >
/ >Thank you.
/
/ Noooo! I found this thread absolutely facinating. Please, please,=
/
/ don't make it go away!

If those involved take this discussion off the list, would you please copy
to Tarek :)

-David
--
"Earn what you have been given."
--
email: dbuehrer@******.carl.org
http://www.geocities.com/TimesSquare/1068/homepage.htm

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