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On 13-11-2012 9:48, Bill Pragnell wrote:
> However, I do not believe the present artifact is supposed to encircle a star,
> or spin like a ringworld (at least not enough to generate significant
> centrifugal forces). I like the idea that it is planet-scaled, generating
> gravity by virtue of its own mass. It is difficult to see how it could form
> naturally of course...
My idea too. A torus with Earth's diameter at least as cross-section to
generate the necessary gravity at the surface; the same composition,
with a molten metallic core (inner torus). The whole structure orbiting
a star... which would probably tear it apart, or free in the
interstellar medium, with a need for a light and warmth source...
Interesting musing... ;-)
Thomas
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Le 13/11/2012 13:04, Thomas de Groot a écrit :
> On 13-11-2012 9:48, Bill Pragnell wrote:
>> However, I do not believe the present artifact is supposed to encircle
>> a star,
>> or spin like a ringworld (at least not enough to generate significant
>> centrifugal forces). I like the idea that it is planet-scaled, generating
>> gravity by virtue of its own mass. It is difficult to see how it could
>> form
>> naturally of course...
>
> My idea too. A torus with Earth's diameter at least as cross-section to
> generate the necessary gravity at the surface; the same composition,
> with a molten metallic core (inner torus). The whole structure orbiting
> a star... which would probably tear it apart, or free in the
> interstellar medium, with a need for a light and warmth source...
>
> Interesting musing... ;-)
Oh yes, what about the magnetosphere ? (magnetotorus ??)
Is there a north pole too ?
(probably, assuming the inner torus has its own revolution speed)
Would the magnetic field looks like the tokamak helicoidal field ?
And for added fun: could such planet have a moon or more ?
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Le_Forgeron <lef### [at] free fr> wrote:
> Le 13/11/2012 07:04, Stephen a écrit :
> >
> > I did some quick calculations and knowing that the centripetal force is
> > equal to minus the angular velocity squared times the radius times the
> > mass (F = -W^2*r*m).
> > If the torus was revolving around its centre once in 24 hours. On the
> > inner surface the force would be about 0.508g and on the outside surface
> > 0.529g. If the period was 12 hours the forces would be 2.03g and 2.116g
> > respectively. Note the sleight of hand going from force to acceleration ;-)
>
>
> There is more than just a delta in the centripetal force. (on the outer
> circle, it is opposite direction of gravity (like on earth); on the
> inner circle, it should be the same direction as local gravity (but the
> local gravity is diminished due to the point being between "two massive
> parts"
Sorry, I hab a told. :-)
I thought that was implicit when I said centripetal and minus.
It is interesting what happens to the vectors at the edge of the torus.
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On 13/11/2012 8:48 AM, Bill Pragnell wrote:
> Not a wobble, if it encircled a star there would be no orbital motion - an
> outright crash! This is the scenario overlooked by Niven in Ringworld, which he
> later retconned with the rim stabilising thrusters.
>
> However, I do not believe the present artifact is supposed to encircle a star,
> or spin like a ringworld (at least not enough to generate significant
> centrifugal forces). I like the idea that it is planet-scaled, generating
> gravity by virtue of its own mass. It is difficult to see how it could form
> naturally of course...
Fair point Bill. But Ed said "It should spin in about 12 hours or 24
hours or so."
Personally I prefer the Culture Orbitals. ;-)
--
Regards
Stephen
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Le 2012-11-13 10:42, Le_Forgeron a écrit :
> Le 13/11/2012 13:04, Thomas de Groot a écrit :
>> On 13-11-2012 9:48, Bill Pragnell wrote:
>>> However, I do not believe the present artifact is supposed to encircle
>>> a star,
>>> or spin like a ringworld (at least not enough to generate significant
>>> centrifugal forces). I like the idea that it is planet-scaled, generating
>>> gravity by virtue of its own mass. It is difficult to see how it could
>>> form
>>> naturally of course...
>>
>> My idea too. A torus with Earth's diameter at least as cross-section to
>> generate the necessary gravity at the surface; the same composition,
>> with a molten metallic core (inner torus). The whole structure orbiting
>> a star... which would probably tear it apart, or free in the
>> interstellar medium, with a need for a light and warmth source...
>>
>> Interesting musing... ;-)
>
> Oh yes, what about the magnetosphere ? (magnetotorus ??)
> Is there a north pole too ?
> (probably, assuming the inner torus has its own revolution speed)
>
> Would the magnetic field looks like the tokamak helicoidal field ?
>
> And for added fun: could such planet have a moon or more ?
>
>
A planetary magnetic field is not needed to protect life on the planet's
surface, you only need a thick enough athmosphere. After all, if it was
/realy/ needed to protect us from solar particles, those do hit us in
the polar regions and would whipe out all life in those areas...
It could have a, or a few, moons if it's far enough and small enough. A
natural satellite the size of our moon would probably need to orbit in
about 4 to 7 months and it may spell doom whatever it's distance. If
it's small enough, like Phobos and Diemos of Mars, they could be much
closer.
Alain
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Am 14.11.2012 00:00, schrieb Alain:
> A planetary magnetic field is not needed to protect life on the planet's
> surface, you only need a thick enough athmosphere.
Veto! A thick atmosphere means high pressure; high pressure means high
temperature; high pressure plus high temperature means hell... see Venus.
> After all, if it was
> /realy/ needed to protect us from solar particles, those do hit us in
> the polar regions and would whipe out all life in those areas...
I'm not so sure about that. The solar particles come in from the side,
where the magnetic field does deflect the particles. They end up in the
Van Allen belts, where due to the shape of the magnetic field they are
confined high above the atmosphere, traveling back and forth between the
poles. AFAIK only a small portion of the particles does make it down to
the atmosphere to create polar lights, and I'd assume they've already
been slowed down a good deal by then.
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Stephen <mca### [at] aolcom> wrote:
> Fair point Bill. But Ed said "It should spin in about 12 hours or 24
> hours or so."
Which is not fast enough for significant centrifugal effects - but just right
for an earthlike day/night cycle. Although depending on its inclination and
rotation axis, the inhabitants might be in for some wacky seasons, and there
could be a lot of secondary light at night.
> Personally I prefer the Culture Orbitals. ;-)
Me too. Mostly for the amenities :)
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"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> Stephen <mca### [at] aolcom> wrote:
> > Fair point Bill. But Ed said "It should spin in about 12 hours or 24
> > hours or so."
>
> Which is not fast enough for significant centrifugal effects -
Are you sure, are my calculations wrong?
> but just right
> for an earthlike day/night cycle. Although depending on its inclination and
> rotation axis, the inhabitants might be in for some wacky seasons, and there
> could be a lot of secondary light at night.
>
> > Personally I prefer the Culture Orbitals. ;-)
>
> Me too. Mostly for the amenities :)
And the snappy repartee. ;-)
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"Stephen" <mcavoys_AT_aolDOT.com> wrote:
> "Bill Pragnell" <bil### [at] hotmailcom> wrote:
> > Stephen <mca### [at] aolcom> wrote:
> > > Fair point Bill. But Ed said "It should spin in about 12 hours or 24
> > > hours or so."
> >
> > Which is not fast enough for significant centrifugal effects -
>
> Are you sure, are my calculations wrong?
Um, I didn't check. Quick calculation of my own, assuming a torus minor diameter
the same as the earth, which gives a major radius of about 6 earths (~77,000km),
spinning once per 12 hours, I get a centripetal acceleration of about 1.6
ms-2... ok, a bit more significant than I thought, that's about 1/6th of a g
more on the inner surface and less on the outer surface.
Athletes from the inner provinces would trounce their opponents from the outer
lands :)
> > > Personally I prefer the Culture Orbitals. ;-)
> >
> > Me too. Mostly for the amenities :)
>
> And the snappy repartee. ;-)
and let's not forget the parties!
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"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> "Stephen" <mcavoys_AT_aolDOT.com> wrote:
> > "Bill Pragnell" <bil### [at] hotmailcom> wrote:
> > > Stephen <mca### [at] aolcom> wrote:
> > > > Fair point Bill. But Ed said "It should spin in about 12 hours or 24
> > > > hours or so."
> > >
> > > Which is not fast enough for significant centrifugal effects -
> >
> > Are you sure, are my calculations wrong?
>
> Um, I didn't check. Quick calculation of my own, assuming a torus minor diameter
> the same as the earth, which gives a major radius of about 6 earths (~77,000km),
> spinning once per 12 hours, I get a centripetal acceleration of about 1.6
> ms-2... ok, a bit more significant than I thought, that's about 1/6th of a g
> more on the inner surface and less on the outer surface.
>
Oops! I forgot to divide bt 9.81 and called m/s^2 g :-(
> Athletes from the inner provinces would trounce their opponents from the outer
> lands :)
>
> > > > Personally I prefer the Culture Orbitals. ;-)
> > >
> > > Me too. Mostly for the amenities :)
> >
> > And the snappy repartee. ;-)
>
> and let's not forget the parties!
If you can remember the parties then you wern't there. ;-)
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