Does our Solar System contain enough material to make a Dyson Sphere the size of Earths orbit? I suspect we’re not even close, even including the gas giants. What about a ring world? Even there, I think we just don’t have enough material by a long shot. But I don’t know the numbers.
Anyone?
A Ringworld is easy - Jupiter has enough mass for the Ringworld as described by Niven.
Ring world
Assume inner and outer radius difference of 10km
Assume radius is centred at 1 AU
Assume a height of 100km
Volume = 9.4e20 cubic meters
Earth volume = 10e20 cubic meters
And by pulling the earth apart it’s actual volume will increase slightly. So 'space" wise you’re good to go. Material, energy and engineering wise is a different story.
Note that Dyson’s conception of his Sphere did not depend on any particular material strength: His model was not for a solid, single-piece shell, but of a whole swarm of independent satellites whose orbits are contrived to give continual coverage over the whole sphere.
Indeed it is. The tensile strength for an object of 1 AU radius rotating fast enough for to produce a significant centrifugal reaction to produce anything like useful simulated gravity would require a tensile strength not only beyond that of any known material by many orders of magnitude, but actually beyond the capability of the molecular and metallic bonding that holds materials together via electromagnetic interactions. This is notwithstanding any practicalities of converting planetary and asteroid resources into some structural material or spinning up and stabilizing the resulting construct.
This is true, but it doesn’t really help. The continuous shell concept at least has the benefit of being statically stable and only needs to be strong enough to resist the normal gravity of the central star at its radius (and could use light and solar wind pressure to help reinforce it, or use a sandwiched honeycomb to stiffen it against buckling). The swarm concept, however, suffers from the same problem as putting multiple similar mass objects in a common orbit but on a massive scale; while the gravitational attraction inside a relatively balanced swarm will be a net zero (except for the central star), self-interactions between the individual components, even if small, will cause the system to become chaotically unstable in short order, which would require constant propulsive stabilization using mass that would exceed charged particles emitted by the central star, and of course the net momentum from captured solar particles would be a net constant positive outward pressure. It is difficult to see how such a scheme would be workable with any conceivable technology on a purely thermodynamic standpoint, much less the functional details of a practical implementation.
Stranger
I’d rather you didn’t, i like being able to see the stars
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That just means that the star has a slightly lower effective mass. It’s still inverse square, so orbits are still stable with it.
Though you’re right that interactions between the satellites, and the resultant dynamic friction, are still a problem.
Viewing platforms. Just descend into the shell, put on a space suit, walk through the air lock and voila! All the stars, none of the light pollution!
One intriguing configuration that I have seen is the ‘snailshell’ or Pokrovsky arrangement, where multiple ‘ringworlds’ with different radii are arranged at various angles to each other, so that they overlap and collect a significant fraction of the star’s luminosity. It isn’t necessary to make these rings rotate fast enough to create earth-like gravity; but if they rotate fast enough to circularise the ring without tearing itself apart, that is good enough for me. The whole shell could have a very low mass, equivalent to a single terrestrial planet, if it were thin enough.
Here’s an image of the concept from Wikipedia, to give an idea of how it works.
And here’s my version - a pair of snailshells around a double star, where a series of rotating habitats are embedded into the rings to give localised gravity.
So the denouement to “Across A Billion Years” wouldn’t happen? Dyson spheres can’t be built?
There are a lot of unanswered technical questions, and even more around if it would actually benefit a society enough to justify the high costs.
A true ridged Dyson sphere would not be orbit-ally stable, and even the assumptions made around the efficiencies in producing it will require massive advances in physics.
Even ring worlds will require discoveries of new physics related to superstrong materials, antigravity, thermally tolerant materials etc…
Freeman Dyson’s plan is most likely impossible in our solar system, and the whole topic is nothing more than hypothesis at this point in time. Freeman expected to dismantle huge portions of Mercury and Venus, and this would make the Earths orbit unstable as an example even if the above problems were solved.
But that said I am glad that people are thinking about it, even if it is not ultimately possible.
I suspect that Dyson Swarms would not be built as some gigantic engineering plan, but rather a long process of accumulation.
Imagine a scenario where a society was chronically short of energy. Someone puts up a solar collector in orbit, and huge profits ensue. As the need for energy continues to grow, more solar collectors are buit. Fast-forward a hundred thousand years, and a significant chunk of the light of the star is now being absorbed by whatever complex aggregation of millions or billions of solar collectors have been put in orbit to capture the increasingly scarce amount of energy available that hasn’t been captured already.
The shape of the thing would be emergent, just as the shape of rail transport networks or shipping lanes are emergent from the negotiations and interactions of the people who have built and expanded those systems over centuries. We might find that Dyson Swams typically only grow to take up a certain percentage of the sun’s output before costs and maintenance overwhelm the advantages.
Or, may e other civilizations aren’t as insane as we are about using nuclear energy and find that sunlight is best left for small scale use and nuclear power makes a whole lot more sense than giant solar collectors.
Make it flat towards the Sun and use a napkin ring design so its volume is only dependent on height. A napkin ring of less than 1.4 mi width has the same area as the surface of the Earth (wet, dry and ice). The volume is then 0.17mi[sup]3[/sup].
Want more space? Move it to 1.4AU and you get 40% more space and the volume stays the same.
The napkin ring theorem is pretty cool Napkin ring problem - Wikipedia
A rigid (I think that’s what you meant to type) sphere is neutrally stable. Ringworlds, however, are unstable.
No it wouldn’t.
That’s just a fancy way of saying “make it really thin, and if you want it to have more area, make it even thinner”. The napkin-ring shape is just one of many possible ways to quantify that, but there’s nothing special about it. In the real world, the thickness would be determined by the properties of the available materials and the needed structural strength, and if you make the area bigger, you’re still going to need that same thickness.
Neutrally stable isn’t very stable though. If some unbalanced force resulted in a slight velocity of the sphere relative to the Sun, there would be no natural restoring force, so a collision would eventually result (unless some other unbalanced force was applied).
As you say, a Ringworld is quite unstable. I did this calculation a while back - the doubling time for deviations from being centered doubles every 8 weeks or so, so in 6 years a deviation of one inch would increase to a deviation of 8.5 million miles (and actually, the doubling time decreases as the Ring gets very offcenter).
Naw, we have enough material to do it (there are various different designs). Ring world certainly we have enough material.
Here are some videos from a guy describing the concept: https://www.youtube.com/watch?v=HlmKejRSVd8
I was referencing unstable as in the timing of winter and summer, not being ejected from the solar system. It was poor word selection, but it will result in changes.
Here is a cite, showing how changes in the orbit of Venus changes Earth’s orbit.
https://eprints.usq.edu.au/32956/1/Horner_Gilmore_Waltham_AV.pdf