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Posted by Kris Krieger on August 2, 2007, 5:54 pm
57g2000hsv.googlegroups.com:
> Here's an interesting thought problem for you folks.
>
> The gravitational acceleration a person experiences is derived from
> the mass of the body we're relating to, and the distance of the person
> from that body's center of gravity. On Earth's surface, this is
> nominally about 9.8 m/s^2, or what we call "one gravity." On
> Jupiter's "surface", the experienced acceleration is much greater.
>
> However, if one could hold a position at 110,000 km from Jupiter's
> center of gravity, one would experience an acceleration of about one
> gravity, making the planetary experience, on the whole, much more
> comfortable. (Radiation belts aside.) If one were to build a shell
> around Jupiter with an outer radius of 110,000 km, one would also get
> a surface area of 19.6 billion square miles, or over 99 times the
> surface area of Earth. *Lots* of living space, and, unlike some other
> celestial megastructures, your atmosphere is stuck to your shell by
> gravity.
>
>
> The question becomes, what would one want to build such a thing out
> of? I don't have a background in mechanical or architectural
> engineering, which is why I come to you folks. I imagine one would
> want concrete, as I picture the stresses forcing the shell to compress
> laterally across its surface. But how much concrete would one need?
> How much water (A scarce resource in space, though Jupiter happens to
> have a large ice moon) would be needed?
>
> Another engineering-related line of thought I can't follow up on is
> the effect of tidal forces...Jupiter has several large moons. How
> much of an effect would they have on the shell?
>
> Incidentally, this is part of a sci-fi world-building project I'm
> working on called Grokked Universe. Here's the relevant thread:
> http://guforum.shortcircuit.us/index.php?topic=38.0
>
>
Well, firstly, the *surface* of your object would have to be around the
altitude you specified. IOW, if you created the object, and then covered
it with a layer of growing medium ("dirt") of x meters, the surface of
the construct would be
110,000 km - x m
from Jupiter's center of gravity.
If your Object is a ring rather than a sphere, you'd also have to have
walls to hold in the atmosphere.
(((IIRC, in "Ringworld", LArry Niven (*IIRC*) had a rig that rotated and
therefore held everything against the inside of the ring.)))
As for materials, isn't a Ni-Fe composite the most common material in the
asteroids? If so, wouldn't that be the logical material of preference?
Certainly, one planet couldn't supply all of the material, at least not
without basically destroying the planet. But it seems to me (jsut on gut
feeling, tho', no calculations) that the asteroid belt might provide
enough material.
I think that destroying Jupiter's moons for the thing is a horrible idea.
Esp. if there is any life on Europa or whatever.
BTW, re: using cables slung from an orbiting body and penetrating a
planet's atmosphere for energy prioduction, that idea has already been
proposed in a science fiction story (might have been by Ben Bova, but I
read it many years ago so can't recall).
A shell around a planet might be less practical than a ring. For one
thing, a rign would be a smaller target for asteroids and comets. For
another, it would allow thermal and other radiation to escape from
Jupiter. ANd then, of coruse, there is the amount of material required
for a shell, as opposed tothe amount required for a ring.
As for holes - well, if you have the tech to do a shell or even ring, you
have to tech to repair the thing....
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