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
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:
What to build from 3D-H ofcaurse ; 3dh is not a material but a method
the only one that in architecture today fir the computer ,and make a
direct link from projecting to manufactoring. But the reson the method
shuld be chosen are, that all it requier is sheet material, that mean
that if you want to build a structure, all you must look for, is sheet
material of some kind , look up 3D-H or 3D Honeycomb --- not the ready
made sheets of honeycomb cubes but the buildng method.
*Want* to build it out of wimmun.
*Have* build it out of unobtanium.
Concrete won't work, not enough strength for a shell that will
support a human.
Enough to drink.
Our Moon swings the Earth around a little circle, and there is a
"three meter high" lump that follows the Moon around. Jupiter is
massive enough that it swings the Sun around a point just outside
the surface of the Sun. You'd have real difficulties keeping the
shell in place.
I'm not worried about the shell staying in place. (See my other
comment about gravitational centering.) I'm more concerned about
stresses induced in the rigid structure of the shell.
I read Dyson's original article, I own all the Ringworld books, and I
just finished reading Niven's "Playground of the Mind" collection. (I
checked it out at the library specifically for the "Bigger than
Worlds" article it contains.)
Dyson doesn't posit a rigid structure. His theory accepts any
structure (or arrangement of structures) capable of capturing and
harnessing all of the energy output of a star. Using it as a
habitable surface poses difficulties in terms of gravity and retaining
an atmosphere. (Though I once calculated that, given all the mass in
our solar system, one could build a a shell around our sun with the
density of the International Space Station, an inner radius of 1AU,
and thickness of 2km. So it's not impossible to inhabit such a
Think for a minute. The shell has to support itself against 1g with a
very tiny curvature, and it will have to support a point mass of a few
hundred pounds. And do all this with 5000 psi maximum stress (or
less). Not in this Universe.
It didn't make sense there either. Displace the centers of mass off
center, and they *will not* recenter without work being applied.
Gravitation is not a force.
Something this size is not rigid. Something the size of a building is
not rigid. And you are right to worry about stresses. I think they
are insurmountable with any matter.
I fear that's a question that only RebarGuy can answer.
I, however, specialize in terraforming, and think it would be far
easier to just terraform Mars, or maybe even Venus or Europa than
build a concrete sphere around Jupiter.
As Pat inspired; if you have the knowledge to build a concrete shell,
your knowledge would likely find it impractical.
The merest of quibbles, I assure you.
It's about gravity.
On the surface of the Earth, you DON'T accelerate. Instead, you find
that a certain force is required from your feet to remain standing.
This is what we usually call weight. So the formulation of g can be
put not as an acceleration of 9.8 meters per second per second, but
rather as a ratio of force(weight) to mass i.e. 9.8 Newtons per
This helps you remember you can move to places some of them near the
poles where the weight due to a given mass is higher, 9.81 Newtons
per kilogram or more.....
Brian Whatcott Altus OK
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
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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