Dyson Sphere

One way to capture the energy output of a star is to build a box and put the star inside it. The box will be spherical, of course (or would it?) - we're trying to economize here.

The idea comes from FreemanDyson. They provide a way to detect advanced civilizations from a distance. If a small, hot star turns into a large, cooler one over a relatively short period (say, a hundred years), it may be because it has been wrapped in a Dyson Sphere. Presumably every civilization will build one when it becomes sufficiently advanced. See DrakesEquation.

Why would anyone build a DysonSphere?

It would visibly signal the technological level of your civilization as soon as construction begins, inviting attacks from any hostile aliens in the region who probably never knew the area was inhabited. Therefore building one can be tantamount to suicide for the entire civilization.

Every organism needs energy and a DysonSphere is the best way to collect all of the energy which would otherwise just be going to waste. Species grow exponentially and their energy needs also grow exponentially even as the energy resources in the universe remain finite. Energy is an extremely scarce resource in the universe and no advanced civilization can afford to let it be wasted.

As for actually constructing a DysonSphere, it isn't too difficult if you have MolecularNanoTechnology and ArtificialIntelligence. I do not believe that it is possible for a starfaring species to lack either of these two technologies. And even as AI makes the construction of a DysonSphere possible, they provide their own motives for such a construction. A community of AI would undergo even more rapid growth than can be conceived of an organic species. The computational power made possible by a DysonSphere would be irresistible and, due to population pressures, would very quickly become absolutely necessary. -- rk

Various kinds of DysonSpheres?, and how to build them How to build a DysonSphere

A DysonSphere doesn't necessarily have to be solid. We can imagine surrounding the star with a shell of asteroids. If the shell is thick enough, the asteroids can be separated enough not to bump into each other, yet each ray of light leaving the star will still hit one asteroid or another. Using asteroids would also maximize the surface area and hence living space.

See http://www.student.nada.kth.se/~asa/dysonFAQ.html http://home.kabelfoon.nl/~cdevoogd/dysonFAQ.html

A partial DysonSphere would still be impressive like LarryNivens RingWorld

A simple example is a Dyson disk, essentially a version of Saturn's rings that extends (almost) down to the solar surface. It will intercept 1/4 of the star's light so its efficiency will be less. But still a lot of power! Interestingly, naturally occurring versions exist.
If an AI civilization built a DysonSphere, they could design it as a single seamless MegaStructure rotating only enough to counteract the gravitational attraction of the star. The computers would be located at the equator and the box would be shaped like a barrel. The top and bottom of the box would have to rely on the solar wind to counteract gravitational attraction. The sides must be angled so that the result of the outward centrifugal force and the inward gravitational force is a force along the curved walls of the box.

A spherical design[, by comparison,] would have the top of the walls push straight down towards the plane of the equator; i.e., inwards and away from the walls. Since everything would press down on the equator, the walls of a seamless DysonSphere cannot be made habitable (even with materials like diamond). Avoiding this limit would require using a series of overlapping rings all rotating around the sun but at crazy angles to each other. Dealing with the complex gravitational forces involved would not be easy. Constructing a DysonSphere for biological organisms seems messy, inefficient and extremely complex. --

That's a StrawMan argument. You've suggested one way to build a Sphere which doesn't work. You can't conclude all ways don't work. See in particular the paragraph about the Sphere not being solid. --

Which changes nothing. Individual asteroids would still have to orbit the star. They couldn't, for example, have orbits centered above the star. Any asteroid that tried to do so would find its orbit falling towards the equator. The difference between unconnected asteroids and connected ones is that nothing would be holding them up in the former case. Disconnecting things isn't magic, it doesn't change any of the forces involved. And since asteroids would all have to follow predefined orbits, it would be simpler to link everything in the same orbit together into a ring. Bingo, you've got the second design I mentioned. Now, if you want to use jets to solve the navigational problems with unconnected asteroids, well you can do the same thing for connected asteroids. The only genuine difference between an unconnected (or loosely connected) and a rigidly connected design is that with the former you can use non-circular orbits. That's it.

That line about using asteroids maximizing living space is a crock. Where does the extra space come from? At the expense of using more material and having less light for a given area. Oh yeah but you can do that by just increasing the size of the DysonSphere. And by that reasoning, why not make the sphere a light-year across? It would make it close to absolute zero in temperature but look at all the living space! "Unconnected asteroids" is used like some kind of magical talisman, an easy solution to hard problems.

I've suggested one way which works for AI. And frankly, that's the only thing I care about. If you think that a human habitable design is possible then it's your job to prove it, not everyone else's to disprove it. Personally, I think the overlapping rings is doable but it's messy, inefficient and extremely complex. There are only a few basic designs possible for a DysonSphere so waving your hands and uttering "there are alternatives" isn't a sufficient response when someone shows one of them is impractical. The "all" in your statement is "two or three" as far as I know and I already accounted for two of them.

There's no reason why all the asteroids have to be in the same orbit. They can be spread out over an arbitrarily large volume of space, so that they don't physically approach each other closely. Nor is there any need for the orbits to be predefined. Making stuff solid reduces our options and probably requires us to use super-strong material when forces try to tear it part. It doesn't buy us anything.

There is plenty of reason to fit as many asteroids as possible into the same orbit. It's the crucial matter of simplifying the geometry of the DysonSphere which is important to fulfill both safety and efficiency concerns. For the same reason, the orbits should be predefined and if possible everything made rigid. It is grossly incorrect that asteroids can be spread out over an arbitrarily large volume of space. An asteroid at 1 LY distance from a star doesn't do anyone any good; it's just a waste of material. All asteroids have to be within the habitable zone around a star. Finally, nothing is gained by having separate asteroids floating around except more surface area with which to lose precious heat.

The extra surface area comes from basic area:volume geometry. Take a cube and cut it in half. We increase its surface area by 1/3rd, i.e. by the two new inner faces. The extra surface area does not come from extra material.

Only lighted surface area counts. If you double the surface by halving the average lighting then you haven't actually doubled the living surface area.

If your main point is merely that it is easier to build environments for computers than for meat, then I agree and you can delete all this.

I didn't have any point to make; I was just creating a quick and dirty model of the thing for my own amusement and others' perusal & critique. Of course, now I do have points to make. My main one would be that "there'll be a cloud of these things" is ridiculous as an argument and as a design.

A note about basic geometry:

If you rotate two points around their common center, you get a circle. If you rotate a circle around its center, you get a sphere. And so on. In some sense, one can think of two points as a 1D circle or sphere just as a circle can be thought of as a 2D sphere.

Differential geometry:

A point on the outside of a spherical shell feels the same force as if from a point source located at the center of the shell. A point on the inside of such a shell feels no force at all. Both effects are due to the fact that although the far side of the shell is farther away, proportionately more mass is located there.

If you lop the top and bottom of a shell, a point on the inside of this shell will now feel a force from the walls of the shell because you've disrupted the exact proportion. A point on the inside of a circular shell will feel a force from the walls of the shell as long as it isn't in the exact center. Naturally, a point inside of a 1-dimensional circular shell (ie, between two other points) will also feel a force if it isn't in the exact center.

The above is why a DysonSphere is passively stable (or passively unstable depending on one's viewpoint) while a RingWorld is unstable.

The simplest arrangement of orbits in a DysonSphere is circular orbits intersecting at two common points, exactly like the lines of longitude on the surface of the Earth intersect at the poles. All the rings would be stacked, one on top of another. Naturally, there would be at least as many rings as the ratio of the width of a ring to its diameter. Thus, if each ring is 1 AU distant from the sun and 1 millionth of an AU wide then there would be half a million rings stacked on top of each other at the poles. Even if they were all 1 km in height, they could easily be fit into the habitable zone so that is not a concern. The gravitational influence of the stacked mass at the poles is a concern. A DysonSphere made up of such rings can't be modeled as spherical but must be modeled as a 3D sphere onto which is added a 1D sphere. The stack at the poles would be compressed together since the rings at the top of the stack would be deformed downwards while the rings at the bottom of the stack would be deformed upwards. Disconnecting the rings into individual modules solves the problem of low intensity tidal forces at the poles, not of high intensity ones. If the tidal forces are low then this is a workable design. Of course, it may still be unacceptably dangerous to have that many stacked orbits close together.

An alternative design which allows for a doubling of the number of poles relies on the fact that an ellipse has two foci. Take an ellipse around a point and rotate it around its axis for a quarter turn so that it covers half of the total spherical area around the point. Now flip the ellipse so that the chosen point is centered at the other focus and resume rotating in the same direction. There will now be four poles; two distant and two nearby / two on each side of the star. By interlocking the individual rings in such a manner, one reduces the edge effects and makes the entire design much more uniform.

I can't think of any simple way to increase the number of poles yet again and by now I have no idea as to the thing's stability anyways.
Maybe don't go with a single star. How about a circular disc located at the center of mass between and perpendicular to two stars in a binary system? Rotate the disc to counteract gravitational compression within the disc itself. You can't live on it since there'd be no gravity to keep you on the surface of the disc, but you could put energy collectors on it on both sides. I haven't done the math on this yet. My guess is that that disc will be passively stable/unstable with respect to stellar gravity although possibly solar wind from each star would help to maintain the disc's central position. Anybody care to do the math on the internal rotation of the disc itself? Can this rotation keep the disc "inflated" in such a way that no exotic materials are required for the disc's construction? -- AndyPierce

It would be actively unstable. To be passively stable, the disc would have to feel no force no matter where it is located between the two stars. In a binary system, the only stable orbits are close to one or the other star, and far from both of them. A stable ternary system has the third star in one of the stable orbits. An unstable system tends to kick out the least massive star IIRC.

To understand the effect of the disc's rotation, you can simplify the binary system into a unary system with the star at the center of the disc. This is because you don't care about the gravitational component perpendicular to the disc. At that point, it becomes obvious that the disc would tear itself apart since the centrifugal force would be increasing while the gravitational force would be decreasing as you go outwards on the disc.

And the disc wouldn't enclose any star. :)

I'd just like to note that the disc would be a gigantic freaking gyroscope. What would this do to its (in)stability? Damned if I know. I have a hundred-page book which attempts to explain why gyroscopes work...
I must admit I was quick to judge and dismiss the seemingly simple suggestion of a Dysons Sphere entirely made of asteroids as a trivial concept merely tangential to the mammoth proportion of complexity required in the planning of a DS project. My initial reaction was actually an audible response, LOL! However, after stirring the idea around in my head since yesterday, the thought occurred to me that a design utilizing asteroids is not such a ridiculous concept as it seems on first inspection.

So far the discussion has revolved primarily around the choice of a physically balanced and stable design configuration.

A sphere may turn out to be the most logical DysonShape? because it obviously provides a uniform distribution of stress in any direction. However, since no current method of construction can be applied to instantaneously produce a complete sphere, consideration is due for the forces which will act upon component structures and their combined segments in various assembly stages throughout the (suggested 100 year) construction term. A stable system of gyroscopic rings is likely to be desirable either as a temporary construction platform and / or as the basis of a structural foundation for the DS.

Availability and cost of materials will also affect the final design choice, and the management of these materials is also no small matter to undertake.

Suppose a target solar system is readily available which already contains sufficient matter for conversion into a DS MegaStructure, or perhaps a star with very close neighbouring solar systems is at hand (uninhabitable of course) whose combined planetary masses would provide sufficient raw materials. In any case, a large quantity of raw material must be persuaded to alter its current momentum (i.e. orbital path) to bring it to a useful orbit proximal with the target star.

The least expensive (costing both energy and time) to initiate a large mass transfer would be to nudge a source planet or its exploded remains at determined opportune orbital moments. Thorough planning, favourable prevailing conditions (favourable solar winds, anyone?) and a strict construction schedule would ensure that little or no additional effort would be required once the armada of asteroids were set en route (Note to self: Hire QuantumComputer programmers to model proposals for all the asteroid delivery trajectories.)

Ideally, the raw materials, whether they be asteroid clusters or entire planetary bodies, would arrive at the correct time more or less (i.e. within precalculated windows of tolerance and with alternate destination timetables) and they should be travelling at a speed to match the relative velocity of the current construction sites. I estimate the foundation structure(s) would rotate very quickly to accommodate the arrival of fast-moving raw materials, and thereafter it would continuously slow down according to the increased structural mass as construction progresses.

Such detailed precision and coordination is paramount to minimize the energy costs - building a "custom brick wall" to stop each gravel truck is too expensive - rather boulders should be catapulted directly from the quarry, reduced to manageable size by in-flight collisions with each other, then each would land softly in or near to their final place in the "wall".

Of course these energy conservation concerns will all be trivial in future DS projects. Once the first sphere has been built energy will have become an affordable commodity, perhaps even permitting future DS designs where a star is ignited inside after the sphere has been built or has been partially completed. '"You bet your asteroid, kid."' -- CarstenKlapp
How are you going to store all this energy so you can get it where you want it?

Antimatter is an extremely compact form.
A HobermanSphere could be useful as a foundation or platform for the construction of a DysonSphere. --CarstenKlapp

How so? Wouldn't a collapsing structure be the last thing you want when looking at a construction platform? -- DanielChurch

IMHO this is actually a fairly neat idea. You could construct the sphere in it's expanded form out at around 1 LY without having to worry too much about gravity and tidal stress. Then collapse it down to 1 AU, lock it and fill in the gaps. --Tim

Actually you might have more success trying to bootstrap from a [http://www.toothycat.net/wiki/wiki.pl?DouglasReay/DysonBubble Dyson Bubble] --Pallando

Question: assuming MolecularNanoTechnology and ArtificialIntelligence then how rapidly could a DysonSphere be constructed in the Sol star system, from the landing of an AI/nanotech probe on a planetoid of one's choice?

Energy is not a limitation and with AI/nanotech, neither is research, design, simulation nor manufacturing. Personally, I don't think it would take more than a few years, a decade at most. -- RichardKulisz

A decade for an ArtificialNanoIntelligence? probe to consume an entire planet is a scary thought, but sounds like a reasonable timeframe with enough material. A tiny nanoprobe (but sufficiently more advanced than the Terminator 2) could land inside an active volcano then proceed to mine the planet from the inside out--like a baby chick, starting out as a speck inside an egg, which grows large enough to be able to perform mechanical (non-nano) tasks if necessary.

How big would a single planet have to be to contain enough matter for a basic paper-thin sphere x distance from a star? Assuming close to 100% of the atoms are used, and all alloys and structures are built with atomic precision. -- CarstenKlapp

On your first scenario. Whatever the technology, it would need a power source powerful enough to consider magma a heat sink. The power source could be antimatter or a heat difference engine but both of those would require substantial matter to work with. Further, survival in magma would require the use of rare elements not likely to be found in abundance anywhere, thus severely limiting replication. The only reason I can think of to tap a planet's core is as a source of energy. A SolarChimney heated by magma instead of the sun and reaching many kilometers in height would provide a lot of energy even in dark environments. Other than that, the sun provides more than enough energy for nanotech devices in space. Using the materials in a planet's core would require cooling them first. This could easily be accomplished by stripping the crust and atmosphere off a planet then repeating the process until there's nothing left. This might take a while.

IMHO, a Uranus-like gas giant might be a better target for a nano-probe. Some advantages: Especially a "hot" gas giant, e.g. one close to the sun, might be a good spot.

-- StephanHouben

A gas giant would be difficult to dismantle with nanoprobes because: The first problem a probe would encounter with a gas giant is that there's nothing to land on. Assuming it was able to float in the atmosphere, it would still have to contend with the thick cloud cover obscuring that giant fusion reactor in the sky we affectionately call "the sun". Zero maintenance and a 5 billion year lifespan, how can you beat that? Wasting material to build another fusion reactor is not something one wants to do. Rather, in a darkened environment it's something one has to do. So given the fact that it would require tons of material when a nanotech probe could otherwise be made smaller than a kilogram, this is far from desirable.

The natural environment of nanotechnology is space, with the bright shining sun on one side and glorious dark space on the other. Planets are for losers, asteroids are where the action will be at. A civilization with space travel and nanotech would have no problem detecting asteroids. Anyone have numbers on the resolution of a telescope array spanning our asteroid belt?

Gas giants can be harvested only with the greatest of difficulty. They would be a secondary stage in the dismantling of a solar system since you need lots of startup material. You start by building a giant space station in orbit. Then you lower a SkyHook? several kilometers into the atmosphere. Then you collect, solidify and move the carbon up to orbit through the SkyHook?. This is an extremely time-consuming and resource intensive process. By comparison, a probe that landed on Earth could immediately build solar collectors, take over the biosphere within a a few days, then start stripping the planet by shooting it into orbit using railguns. This is only possible because you can be where the carbon is abundant and still receive light.

If one went to the effort then Uranus would be useful to harvest, quite unlike Jupiter which is made up of > 99% non-metals (hydrogen and helium).
Is this >99% mass or >99% volume we're talking about here? In any case I think that a 99% atmosphere to core ratio is too high of an estimate.

That's 99% of the entire planet's bulk mass. Jupiter has a liquid hydrogen core. If Jupiter actually had a solid core made of metal then believing it to make up as much as 1% of its bulk mass would be crazily overoptimistic. Jupiter is basically a proto-sun.

Can anyone expand a little on spectral analysis in this context? Is it any easier to detect the presence of hydrogen than it is to detect say, carbon or iron?

Say a nanoprobe already has enough hydrogen (collected from solar winds via a "sail" during its travels, or whatever). Could the gas of a Gas Giant be converted into a more useful state through oxidation? How long would it take to burn Jupiter's atmosphere, using powerful lasers or orbital nuclear bombardment to ignite the atmosphere?

Jupiter has little or no oxygen and any oxygen it has is already be bound in H2O so there is no free oxygen to oxidize anything.

I remember some kind of speculation that a GG's core might be a very dense material like diamond, this would be useful building material. I'll try to find more info on this. -- CarstenKlapp

The emphasis is on like diamond. I bet they're talking about metallic hydrogen.

No, the speculation is that there might be some sort of solid core, made of heavier elements, lower down than the metallic hydrogen. But it would only be about terrestrial-sized, isn't that easy to get to, and would undoubtedly undergo phase changes if you tried to take it out.

I found a page that said something to that effect except it didn't have any details (not even the hypothetical size). Are there any useful references on the web about planetary composition? I never took the astrophysics class and I didn't even recall that Jupiter and Uranus had very different composition.

Only thing I care to find at the moment is http://seds.lpl.arizona.edu/nineplanets/nineplanets/nineplanets.html

I don't know who started it, but I first read about a possible diamond core for Jupiter in ArthurCeeClarke's 2010: Oddesey Two. As I recall, he hypothesized that over the millennia all the carbon that used to be in the atmosphere worked its way downwards to the core (through gravitation) and were compacted into a big diamond of around the size of the Earth. -- GavinLambert
How would oxidation help you? There isn't much oxygen available. Remember, it's almost all hydrogen.

I was thinking about burning off the atmosphere as an easier way to get at the core, and burning it would also convert the gas into something else hopefully more useful. -- Carsten

Now, if your nanoprobe can utilize fusion to transform hydrogen into other elements, you can get away with this. Presumably, this is what Clarke's TMA2 (I can't remember the Russian name he gave to it later) did to Jupiter. -- RobertWatkins

Wasn't that the Monolith? -- GavinLambert

Assuming you're talking about using hydrogen in fusion reactors then it's too slow and inefficient. Using tons of material in order to create (micro?)grams of metal (anything heavier than helium) per year is a losing proposition. If you're just talking about igniting Jupiter (eg, using a black hole) then why not fling it into the sun and be done with it? See also MegaStructures

"Fling it into the sun and be done with it." (An AI with a sense of humour, I love it! THIS PLANET IS IRRELEVANT. LOL. BEGIN DISPOSAL PROCEDURE. LOL.) -- Carsten

The main point of stellifying Jupiter is getting more energy out of it. Flinging it into the sun won't work; that is, it won't get you a lot more energy than the sun is already producing; considering that you will have to deal with its kinetic energy, Mv*v/2, I dare say that it's not what you'd want to do. -- MihaiCiumeica?
Getting back to the title topic for a moment - why would you want a Dyson sphere? Put a big magnetic bottle around the sun and drain it into a few thousand Jupiters and you can mine them for hydrogen as you need it to run your streetlights and space heaters for trillions of years (or even higher powers of 1000, depending on your population). StripMineTheSun?!

Obviously you've missed the fact that the sun is a thermonuclear fusion reactor. An eminently safe, cheap and utterly practical one that ALREADY EXISTS. We don't have to deal with containment, radiation, fuel, waste, radioactivity, nor even construction. All we have to do is gather the generated power. So why would we want to demolish a WORKING giant nuclear fusion reactor in order to create lots of hypothetical useless itty bitty ones?
He has a very good point.

The stars burn out faster the larger they are, radiating energy at a rate defined by their size. if we tapped out the hydrogen into cool protostars, they would act as giant hydrogen gas bottles and the lower gravity should cease fusion at the core. shipping the hydrogen to fusion reactors on earth and the initial transfer of hydrogen would use a lot of energy, but that is somewhat offset by the increase in the life of the solar system as energy is produced on demand, not by natural runaway processes. this way, we could even keep the other planets and any life on them as nature preserves. when a Dyson sphere is built, the solar system becomes dark and cold, lit by power directed towards it by the builders of the Dyson sphere and power transfer devices.

by shipping out hydrogen and putting reactors in orbit around each planet, where a Dyson sphere could be attacked by terrorists and the power go off-line, with shipped hydrogen, each world would have its own mini sun in orbit that can run until on board hydrogen is depleted. worlds inhabited by sentient species would have local fusion units and may prefer to not have a wasteful fusion reactor in orbit.

the mini sun in orbit around Neptune for example, would have very low power requirements as it would only have to match the light that would have reached Neptune from the sun.

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