Megastructures

[Q99]

Megastructure talk!

Ringworlds, Dyson's Spheres, Halos, the City from Blame!, the Grand Central Arena Arena, and more.


What do you think of different Megastructures, and what are some of your favorites?

[Zeropoint]

I'm going to say an Orbital Ring because one features in one of my favorite manga, they give very cheap access to space, and we could build one with the tech we already have if we wanted it more than we want war.

Err, I guess I should say a bit more.

I tend to favor the physically plausible megastructures. The original Ringworld, for instance, would have to support tensile stresses that are simply out of theoretical reach for materials made of atoms as we know them. Thus, as admittedly cool as it is, it ranks lower in my mind.

Ooh, my other favorite is the matrioshka brain.

[Q99]

I'm going to say an Orbital Ring because one features in one of my favorite manga, they give very cheap access to space, and we could build one with the tech we already have if we wanted it more than we want war.

Yea, I like those too. Battle Angel Alita Last Order has one.

Err, I guess I should say a bit more.

I tend to favor the physically plausible megastructures. The original Ringworld, for instance, would have to support tensile stresses that are simply out of theoretical reach for materials made of atoms as we know them. Thus, as admittedly cool as it is, it ranks lower in my mind.

On the flip side, I diverge with you there ^^ I like Megastructures with interesting features, so Ringworld with it's stabilizing jets, day/night panels, and star-beam defense are in my favor.


The Arena I mentioned in the original post is such an example. It's... mind-bogglingly huge and advanced, even by Megastructure standards, but it's special features make it a place with a lot of things to learn about, and importantly also make it a meeting place for all the various starfaring species in the universe.

Ooh, my other favorite is the matrioshka brain.

Which is where our likes come back together ^^ That definitely counts as having cool special features!

[Isolder74]

I have to think that one of the largest mega-structures ever seen in Sci-fi has to be the Star League's Frontier from the Last Starfighter. The thing absolutely massive.

[Purple]

I'd have to say that as far as megastructures go my favorite design is the O'Neill cylinder. Sure it's not as massive as some of the others but on the plus size it's plausible. And there is nothing quite as beautiful to imagine as looking up to see the earth all around you.

[Me2005]

I'd have to say that as far as megastructures go my favorite design is the O'Neill cylinder. Sure it's not as massive as some of the others but on the plus size it's plausible. And there is nothing quite as beautiful to imagine as looking up to see the earth all around you.

I like either O'Neill Cylinders or Stanford Tori or other wheel-station. Much less mega, but still awesome and the signifier of a real space-age IMO.

[Starglider]

I have to think that one of the largest mega-structures ever seen in Sci-fi has to be the Star League's Frontier from the Last Starfighter. The thing absolutely massive.

Not a contiguous structure, but the Cultureverse has something functionally equivalent and much larger; a network of force field generators designed to shield the entire galaxy. The individual generators are artificial planets (with layered onion structure). The airspheres from Look to Windward were also quite interesting, although not physically plausible (more of a ´sublimed civilisation did it somehow´ artifact I think).

[Q99]

One of the biggest is the Xeelee Ring from the Xeeleeverse. Make a, well, basically a ring-shape black hole the size of a galaxy, with a naked singularity in the middle, as an escape hatch for the universe.

If one calls that a megastructure- while artificial, it is simply a spinning cosmic string.

The Arena, which I keep mentioning, is a huge construct that basically fills the 'hyperspace' of the setting. For each star system, there's a smaller hollow planet-sized 'sphere,' that contains a model of said star system within. When one FtLs, one arrives in the sphere in a place corresponded to the model and vice-versa (i.e. leave from near earth, appear near model earth. Leave from near model jupiter, appear near real jupiter). The Spheres contact to a central hub, the Arena, and have openings that allow one to traverse between spheres as well- and the area between them is full of stuff, including life. It's a giant ecosystem in it's own right.

[biostem]

Is there a reason you'd want a ring structure instead of just some independent space stations? Other than the increased surface area, does it provide any advantages?

I've always been a fan of independent structures - something like a giant space vessel that housed its own biosphere and was self-sufficient.

[Zeropoint]

The advantage of a really big ring is spin gravity, and that if it's big enough, you can build walls tall enough to keep the air in without a "roof", which simplifies some forms of getting in and out. The space station in Elysium was built that way, although it was nowhere near big enough and would not have been able to maintain a habitable air density as depicted.

[Q99]

Is there a reason you'd want a ring structure instead of just some independent space stations? Other than the increased surface area, does it provide any advantages?

It's often *much* more efficient material wise.

A whole bunch, you need station keeping, you need walls, you need life support for each, computers to run each, people to run each, etc.. A lot of redundant stuff.

A megastructure, there's a lot of stuff you only need to do once, and a lot of stuff that benefits from efficiency of scale. Once you've got a really big biosphere going, it somewhat regulates itself.

I've always been a fan of independent structures - something like a giant space vessel that housed its own biosphere and was self-sufficient.

Like Eldar Craftworlds, colony ships like Sidonia, and similar?

[Simon_Jester]

In some science fiction settings (typically those with non-Newtonian propulsion), it is practical to make a planet-sized ship by literally bolting engines onto a planet; that might be an interesting subtype of megastructure.

Edward Elmer Smith's Lensman setting, for instance, dates back to the pulp SF days of the 1940s, and features inertialess drive technology being applied to a planet so that its inhabitants can escape the control of a growing and malevolent galactic empire. When generalized to other planets they become, in effect, mobile fortresses in space warfare.

[biostem]

It's often *much* more efficient material wise.

A whole bunch, you need station keeping, you need walls, you need life support for each, computers to run each, people to run each, etc.. A lot of redundant stuff.

A megastructure, there's a lot of stuff you only need to do once, and a lot of stuff that benefits from efficiency of scale. Once you've got a really big biosphere going, it somewhat regulates itself.

But with something that large, and assuming you'd have thousands or millions of inhabitants, (billions or trillions even), wouldn't you want multiple overlapping/redundant systems anyway? And for things like water distribution, surely you'd want local pumping/filtration/recycling systems as well? The same, I imagine, would hold true for atmospheric/climate control system, computer systems, and so on... so would you really save anything here?

As for the comment about spin gravity and walls to hold in the atmosphere - couldn't you achieve this by just moving the station around at sufficient speed, (or am I missing something else here). Plus, with smaller stations, you could reconfigure their orbits more easily.

Like Eldar Craftworlds, colony ships like Sidonia, and similar?

I'm only somewhat familiar w/ the Eldar from WH40K, so I don't know about their Craftworlds. I have watched the 1st season of Knights of Sidonia, but I was also thinking of the living tree-ships from Tenchi Muyo or that one movie from the 80's where the ship had a little biosphere and there was that helper robot... silent running or something was its title.

[Q99]

But with something that large, and assuming you'd have thousands or millions of inhabitants, (billions or trillions even), wouldn't you want multiple overlapping/redundant systems anyway?

Sure, but with the scales of megastructures, you can get great redundancy with far less investment.

And for things like water distribution, surely you'd want local pumping/filtration/recycling systems as well?

Some stuff isn't redundant, yea... but here's the thing, you get that from a *pipe* on a megastructure, rather than a supply ship.

If the pipe breaks down, someone can take a train, car, airplane, etc. carrying water. Or an alternate pipe route.

Every space station needs extensive pumping/filter/recycle system and/or regular external supply runs.

Every settled piece of a megastructure only needs to be within pipe or train range of something that does.

If you're 50 miles from a major water source on a megastructure, that's no big. On a space station, very big deal.

The same, I imagine, would hold true for atmospheric/climate control system, computer systems, and so on... so would you really save anything here?

Yep, a heck of a lot. Atmospheric/climate control, you only have one atmosphere in a megastructure, and size itself helps with some problems. Computers, you've got far more processes just going into separately sustained each individual one. Some processes only need to be done once, some only once for every X amount of area. A smaller station needs checks on all the hatches in an area near a vacuum, it needs to regulate heating and cooling *without* a gigantic mass of atmosphere to dump it in a spread it around, and thus have to worry about levels of coolant and other things... there's a heck of a lot of stuff that does need to be duplicated for every single thing, but only one or a few of on a large scale thing.

Even many things that you'll need more than one of, you'll still need a lot fewer of.

And that's just systems. Talking mass, every floor, ceiling, and wall facing vacuum must be fairly thick and secure. You're using a lot-lot-lot of material on keeping vacuum on it's side of things if you're trying to get massive living space from many individual stations.

Consider that we're often going to be talking one instead of millions of individual smaller units.

As for the comment about spin gravity and walls to hold in the atmosphere - couldn't you achieve this by just moving the station around at sufficient speed, (or am I missing something else here).

That's constant acceleration/constant fuel use you're talking about to provide acceleration-gravity, while a ring is simply momentum. Once it's up to speed, you don't have to do much.

Plus, with smaller stations, you could reconfigure their orbits more easily.

True, but we're talking habitats anyway, and how often do you want to move orbits?

I'm only somewhat familiar w/ the Eldar from WH40K, so I don't know about their Craftworlds. I have watched the 1st season of Knights of Sidonia, but I was also thinking of the living tree-ships from Tenchi Muyo or that one movie from the 80's where the ship had a little biosphere and there was that helper robot... silent running or something was its title.

A Craftworld is like Sidonia or the Silent Running, but much bigger. Size of a small moon, often.

Treeships use pocket dimensions, so that's cheating ^^

[NoXion]

I did some calculations because I was curious.

For a population of a trillion people, a Ringworld provides 942km2 of space per inhabitant, assuming an inside radius of 1AU (1.5e8 km). That's a hell of a lot of room, especially when one considers that human inhabitants are likely to congregate in settlements. For any population size of less than a trillion there would be an effectively post-scarcity situation with regards to land - something that would be completely unprecedented in all but the most advanced of star-faring civilisations. I've sometimes tried to imagine what the implications would be if a young interstellar human civilisation happened to discover an uninhabited but habitable Ringworld. You might not be able to afford a broom cupboard anywhere back on Earth, but on the Ringworld land could be cheap enough for you to buy the equivalent of a whole national park to retire on. One of the larger ones.

Let's crank up the absurdity a few notches.

How big could a Ringworld be around a star with a larger habitable zone? Let's use Deneb as an example. Using this page to calculate the habitable zone, we get an answer of 179AU for Deneb (luminosity 20,000 times Sol), rounded up. Using the same calculations as before, we get an inside radius of 1.69e11 km. Multiply that by 2e8km (i.e. scaling up the height of the Ringworld to 1e8km to roughly maintain the previous proportions), we get 3.38e19km2! That's 33.8 million square kilometres for every member of a trillion-strong population! Whoever builds such a thing must really like their living space.

"Tired of shelling out over the odds for wasteful, expensive planetside property that gets hit by asteroids or trashed by intergalactic warfare? Buy more land for less cost on the GigaRing! Each massive plot comes with a lifetime guarantee* of protection thanks to the star-laser!" *Offer time-limited to 5 million years

Dyson spheres would provide yet more magnitudes of space, not only because of their greater surface area, but because I suspect you'd have to place their inner habitable surfaces a bit further out than with Ringworlds due to heat dissipation issues.

Wild number-free imagineering starts here:

But depending on how you look at things, even a standard Dyson sphere has a lot of space simply going to waste. If you can meet the absolutely ridiculous technological and material demands, wouldn't a solid Dyson sphere - that is, a sphere with its superstructure extending all the way down to the star's surface or even into its outer layers - provide even more space than that?

The first problem that crops up for me at least would be that the issue of heat dissipation, potentially problematic for standard Dyson spheres, would be utterly monstrous for a solid version. I imagine that waste heat would have to be funnelled into many "firewells", roaring great tubes filled with expelled plasma from the star, emerging to erupt on the sphere's surface like the flare stacks of the Titans. This would give the sphere a suitably Hadean appearance from the outside, and over time it would not surprise me if some kind of external atmospheric envelope were to build up, due to the solid mass of the interior providing more gravitational pull than the hollow version. It could end up looking like a stupendously large planet!

Speaking of gravity, the physical forces and material requirements involved in such a structure would, I imagine, be far more demanding than that of a Ringworld. You would need something that's not only strong on the order of Ringworld-material (perhaps stronger), but it can't be too heavy/dense either. That wouldn't matter so much in the deeper layers of the interior, but if you want unmodified humans to be able to live in the outer layers without being crushed by the gravity, or be forced to use yet more superscience-y artificial forcefields to protect them, that's something you have to consider. You'd probably have to invent a whole range of super-materials to make a solid Dyson sphere work. Also those firewells I mentioned will have to be made out of the best insulating material in the universe, or most (all?) of the interior will cook ordinary human inhabitants to death. You'd also need similarly powerful heat conductors or something along those lines.

Maybe a compromise solution would involve a series of hollow Dyson spheres enveloping a star, like a Matryoshka doll. You'd need to provide illumination for all but the innermost sphere. With enough layers it might be possible to live on the outer sphere, with illumination perhaps being provided by a companion star or some other means.

In any case, a volumetric Dyson sphere that was discovered rather than constructed would have many orders of magnitude more in terms of unexplored territory than a Ringworld. Even without intelligent inhabitants, evolution could take many strange turns in such a world. A civilisation capable of building such things would be fearsome indeed. Although more fearsome would be the answer to the question of why the civilisation that built such a thing is no longer around...

[Q99]

But depending on how you look at things, even a standard Dyson sphere has a lot of space simply going to waste. If you can meet the absolutely ridiculous technological and material demands, wouldn't a solid Dyson sphere - that is, a sphere with its superstructure extending all the way down to the star's surface or even into its outer layers - provide even more space than that?

The original Dyson's sphere concept was more about power than living space, of course. It does seem unlikely one would need very much more living space than a normal thin sphere- or at most, a multi-layered one.

Though, of course, there is one SF that does so and then some- The City from Blame.

Only it doesn't go out to Earth's orbit. No, it goes out past Jupiter's orbit.

And it wasn't exactly purposeful- someone told the builders to 'start' and then the off switch broke. So, yea.

The tech used in supporting it is rather impressive, to say the least.

[biostem]

With a Dyson sphere, you could have the inner surface of the sphere setup like the surface of the Earth, and the outer surface could be more like typical scifi space station, (only benefitting from having a direct link to the more normal environment on the other side of the sphere).

For such a structure, would it make more sense to setup some sort of rail or elevator system, or would you be better off using ships to travel to points on the inner surface?

[Korgeta]

In some ways I think of megastructures in sci-fi as the ultimate vanity project akin to how ancient and some modern civilizations build to reflect wealth, symbol and power yet not all such [rojects were beneficial. I imagine that creating a sphereworld etc must have a purpose beyond just increased habitation space when at that stage the entire galaxy would be at your disposal. Then again the news is buzzing over some mysterious 'structure' in space right now..

The tenchi series, for as much as it was basic on its story had some nice visuals of megastructures, Tenchi Universe in particular with a double orbital ring on Jurai homeworld is still one of my favourite mega structure designs in just how it visually appears and answers with imagery how far advanced Jurai was without going into detail.

Other then that I haven't come across much megastructures in sc-fi (save the death star of course), though I played space empires V once and completed a sphere world it was HUGE, it was simply limitless.

Would the death cloud from Babylon 5 be classed as a megastructure?

[Q99]

Iirc Tenchi GXP has the Galaxy Police HQ be a triple-ring.

And the Abh from Crest of the Stars has, as their capital, a framework Dyson Sphere close to a star (not covering the whole thing, just hexagonal struts), which is the biggest fuel production center in the galaxy. Most people in the system live on a much smaller space station.

Would the death cloud from Babylon 5 be classed as a megastructure?

Yep, it's solid framework can surround an entire planet.

With a Dyson sphere, you could have the inner surface of the sphere setup like the surface of the Earth, and the outer surface could be more like typical scifi space station, (only benefitting from having a direct link to the more normal environment on the other side of the sphere).

For such a structure, would it make more sense to setup some sort of rail or elevator system, or would you be better off using ships to travel to points on the inner surface?

A combination. Rails for relatively short journeys, but catching a flight for the long ones.

[biostem]

A combination. Rails for relatively short journeys, but catching a flight for the long ones.

I suppose, depending upon the tech level we're talking about, they could even use near-star flight paths to get to the completely opposite side of the sphere's inner surface as well...

I wonder how such a civilization would handle the solar flares that inevitably come off the star - perhaps large movable shields that could move between the section of the surface that would be hit, or maybe just some form of theater energy shield?

[Q99]

I wonder how such a civilization would handle the solar flares that inevitably come off the star - perhaps large movable shields that could move between the section of the surface that would be hit, or maybe just some form of theater energy shield?

If they're an AU out, a solar flare would be no worse for them than it is for us.


And even if a bad, dangerous one happened- it's localized, and likely quite predictable. They have the option of evacuating an area.

[Simon_Jester]

One big problem with ringworlds and inhabited, solid Dyson spheres is gravity.

If you put a ringworld in a stable orbit around the star, it will stay up on its own, but the ring will be in microgravity- everything is in a stable orbit about the star, so the ringworld floor doesn't have to exert any force to hold you on your current (circular) trajectory, any more than the floor of the space shuttle exerts any force on the astronauts. Inhabited, solid Dyson spheres have the same problem at the equator.

Moreover, a solid Dyson sphere is NOT in a stable orbit anywhere BUT at the equator, because individual chunks of the shell cannot possibly be moving on the same trajectory as a free-floating chunk of orbiting matter.

Now, with a ringworld you can solve this by constructing a roof to hold the atmosphere in and just accepting that the population will be in microgravity. Or you can put a few big, multi-thousand kilometer pancakes of rock under select parts of the ringworld's outer surface to create downward gravity in the areas you want people living in... although the average solar system does not contain enough raw materials to do this on any great scale.

With a Dyson sphere, the problem is not solvable- a Dyson sphere is not stable as a single, rigid spherical shell unless you break out 'scrith.'

'Scrith' is Niven's term for the material of HIS ringworld... because his Ringworld was spun for gravity like an O'Neill cylinder. The problem is that to spin something that large that fast, you need to have it spinning at something like 770 kilometers per second, and the centrifugal forces are insane. He did some math and concluded that he'd need the Ringworld to be made out of a material with tensile strength comparable to that of a single atomic nucleus. Utterly unphysical- but Niven never let that stop him from telling a good yarn, and the indestructibility of the Ringworld floor material became a useful plot point.

I don't know exactly what you'd need to build a stable, rigid Dyson sphere, but it'd probably need to be a comparably insanely strong material.

[NoXion]

You'd also need to be able to manufacture large amounts of highly reliable and energy-efficient redundant gravity generators if you want to be able to live on the inside surface like on a planet.

If such a structure were to be constructed by some long-gone race and then discovered by an interstellar human civilisation, they might find that since then parts of the Dyson sphere have lost gravity because bits of the extremely useful gravity generation equipment have been looted by previous discoverers.

I wonder what effect that would have on the internal environment. Maybe massive storms created by atmospheric updraft?

[Starglider]

Now, with a ringworld you can solve this by constructing a roof to hold the atmosphere in and just accepting that the population will be in microgravity. Or you can put a few big, multi-thousand kilometer pancakes of rock under select parts of the ringworld's outer surface to create downward gravity in the areas you want people living in... although the average solar system does not contain enough raw materials to do this on any great scale.

The materials requirements are still going to be essentially impossible. Considering a single earth-mass of rock supported by weightless strut 1000 km wide by 1km thick, the strut material will be subjected to about 35,000 GPa (naive arch model). For comparison diamond has a compressive strength of 300 GPa ish, and is obviously not weightless. There are some vauge concepts for unconventional materials that could be strong enough, but they're science fiction at this point. It would be more sane to just build lots of spinning ring habitats and thread them onto the rigid ring, if you are neurotic about your station-keeping thrusters failing or something.

[Q99]

A Dyson's sphere is honestly more realistic than a ringworld- or at least a spinning ringworld. Stellar pressure is what it uses to keep shape.