Alderson Discs
James Nicoll
fantasy campaign and alderson discs strike me as a possible
alternative for a world shape.
So, ignore for a moment that it's a fantasy setting:
what were the characteristics of an AD, aside from being a
thin disc around a star with a hole in the center for the
sun to bob up and down through?
I'm assuming that the disc can't extend much farther
in than about an AU for a sunlike star or much farther out
than perhaps 1.5 AU. There's still a heck of a temperature
difference there to drive weather, although I wonder what
scale the weather systems would be on. Ignoring heat transfer,
the temp range might be from 50 degree C to -50 out in the
boonies away from the sun [Or worse: how do you calculate
the weather and climate ranges on an AD?]
Living area isn't bad: I get about 340 million Earths,
counting both sides.
How thick are ADs supposed to be?
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JWMeritt
> So, ignore for a moment that it's a fantasy setting:
>what were the characteristics of an AD, aside from being a
>thin disc around a star with a hole in the center for the
>sun to bob up and down through?
Big. Really, really big. Check Niven's "Bigger than Worlds"
>How thick are ADs supposed to be?
What is it made of? Neutronium? Iron? Silicon Dioxide?
I'm going to assume that you want (as a minimum) a partial pressure of oxygen
sufficient for Homo sapiens (say, Andes settlement?) without pure O2.
James W. Meritt, CISSP, CISA
Senior Information Systems Security and Audit Analyst
Information Assurance Center of Excellence
Getronics Government Solutions
James Nicoll
JWMeritt <jwme...@aol.com> wrote:
>James Nicoll wrote:
>> So, ignore for a moment that it's a fantasy setting:
>>what were the characteristics of an AD, aside from being a
>>thin disc around a star with a hole in the center for the
>>sun to bob up and down through?
>
>
>Big. Really, really big. Check Niven's "Bigger than Worlds"
Read it when Nixon was in office.
>>How thick are ADs supposed to be?
>
>What is it made of? Neutronium? Iron? Silicon Dioxide?
It has to be unbelievably strong. Consider just the
stress from the fact that the inner edge wants to orbit the
in a year [I think] and the outer edge in two, assuming it
doesn't collapse into a sphere first. What's the various
strengths of neutronium?
Erik Max Francis
> It has to be unbelievably strong. Consider just the
> stress from the fact that the inner edge wants to orbit the
> in a year [I think] and the outer edge in two, assuming it
> doesn't collapse into a sphere first. What's the various
> strengths of neutronium?
Unless you want a sphere that's the size of a neutron star, it won't do
the job. Neutronium isn't table unless under sufficient gravity.
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Anders Sandberg
> James Nicoll wrote:
>
> > It has to be unbelievably strong. Consider just the
> > stress from the fact that the inner edge wants to orbit the
> > in a year [I think] and the outer edge in two, assuming it
> > doesn't collapse into a sphere first. What's the various
> > strengths of neutronium?
>
> Unless you want a sphere that's the size of a neutron star, it won't do
> the job. Neutronium isn't table unless under sufficient gravity.
The neutronium is mainly there for gravity. I would guess some active
framework like massive electromagnetic mass streams would be useful to
keep things in place. Place a grid of radial and circular pipes filled
electromagnetically accelerated pellets in the disk to stiffen it.
--
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Urban Fredriksson
James Nicoll <jam...@babbage.uwaterloo.ca> wrote:
>In article <20001211132940...@ng-cg1.aol.com>,
>JWMeritt <jwme...@aol.com> wrote:
>>James Nicoll wrote:
>>> So, ignore for a moment that it's a fantasy setting:
>>>what were the characteristics of an AD, aside from being a
>>>thin disc around a star with a hole in the center for the
>>>sun to bob up and down through?
Gravity perpendicular to the flat surface (as long as
you're not near the edges) which doesn't decrease with
distance (again only as long as you're far from the edges
compared to the surface). Shape the edges right and you
can walk round them.
Weather pattern will mostly be winds towards the inner,
warmer edge where the air rises and circulates out. Weaker
winds the further out you get.
You probably don't want a single gigantic cell, so
there should be bands or patches which absorbs radiation
differently so it's not always warmer in one direction.
Perhaps lots of concentric ocean rings?
I'm not clear if this could really prevent continous
gigantic winds, so perhaps there would be 10+ km
[transparent?] walls partitioning the surface in rings or
perhaps cells.
To some extent climate could be adjusted with altitude, so
the air might be thicker the further out you get. Which
gives me the idea of a transport system which uses gravity
to get outwards and sails to get inwards.
>>>How thick are ADs supposed to be?
Depends on what gravity you want. I think you can make it
different thicknesses if you want different gravities
(just making it of different materials would make the
high-gravity zone "lower" and that could be pretty
impractical) and shape it so the surface is "flat". Well,
not if you use something superdense of course.
>>What is it made of? Neutronium? Iron? Silicon Dioxide?
I think whatever you make a ringworld out of would do.
> It has to be unbelievably strong. Consider just the
>stress from the fact that the inner edge wants to orbit the
>in a year [I think] and the outer edge in two, assuming it
>doesn't collapse into a sphere first.
It's _not_ in any kind of orbit around the sun because
there's no reason for it. I'm not sure you want to spin it
at all, unless to get Coriolis forces.
The supporting structures inside it could of course be
rotating and at different speeds.
But perhaps this is the wrong way of seeing it. If
we're going to get slightly more realistic the main mass
of the disk might be lots of rotating massive rings and
the surface just a thin cover.
--
Urban Fredriksson http://www.canit.se/%7Egriffon/
To get rid of an enemy, make him a friend.
James Nicoll
star takes to bob up and down through the central hole?
Jim Davies
>>Big. Really, really big. Check Niven's "Bigger than Worlds"
>
> Read it when Nixon was in office.
Why, did he keep you waiting?
>>>How thick are ADs supposed to be?
>>
>>What is it made of? Neutronium? Iron? Silicon Dioxide?
>
> It has to be unbelievably strong. Consider just the
>stress from the fact that the inner edge wants to orbit the
>in a year [I think] and the outer edge in two, assuming it
>doesn't collapse into a sphere first. What's the various
>strengths of neutronium?
Now you're not thinking. Why not partition it into rings a few hundred
km across, each sliding past the next? Let's assume a tongue and
groove arrangement with suitable unobtanium ballbearings.
Let's assume a disk where g=wv to cancel out the forces: therefore it
has an angular velocity of 2pi per year. So a 1000km ring segment will
be moving at 6283 km/year past its neighbours, equals 0.7 km/h. That's
not very much.
Actually, is the disk sort of U-shaped in cross-section? ie, thicker
at the inner and outer edges. Towards the centre, gravity towards the
star would be more than the "centrifugal force" outwards, so you'd
feel a lateral pull towards the star. And conversely at the outer
edge. So you'd need to bend the ground up to compensate.
-
Jim Davies
----------
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