## [Challenge Companion] Megastructures

* Author: u/alexanderwales  *Time flies like an arrow**
* URL: https://www.reddit.com/r/rational/comments/5nfxjd/challenge_companion_megastructures/
* Score: 17

* Created: 2017-01-12T00:12:35

### Post:

**tl;dr: This is the challenge companion thread, where you can post ideas, recommendations, etc.**

I think one of the primary challenges facing [megastructures](https://en.wikipedia.org/wiki/Megastructure#Theoretical) *in fiction* is that they're a little more interesting as structures than they are conducive to stories. A lot of word count typically gets spent describing the grand scale, the engineering, and all that sort of stuff, but none of that is actually a *story*. Stories need conflict, and while conflict can take place on a megastructure, the megastructure qua megastructure doesn't provide easy springboards for conflict.

Authors solve this in different ways. Wars that take place within or on the megastructure are common. Exploration is also common (usually Man vs. Nature type conflicts). Sometimes the megastructure has some flaw to it that needs to be corrected ("The Ringworld is unstable!"), or the original builders have left and the megastructure is deteriorating in some way. Other times the megastructure is a weapon (like the Death Star), which tends to be much more interesting.

Some reading:

* *Ringworld* by Larry Niven
* [*Missile Gap*](https://www.fanfiction.net/s/11685932/1/Instruments-of-Destruction) by Charles Stross
* *Matter* by Iain M. Banks

But again, it's a very common scifi trope. The supertrope is [Big Dumb Object](http://tvtropes.org/pmwiki/pmwiki.php/Main/BigDumbObject), but that's a troper definition, which revolves around a specific narrative role rather than strictly describing a megastructure. The trope is less common in fantasy, depending on what you define as a megastructure (does Sigil, City of Doors count?).

### Comments:

> **u/lsparrish** [+11]  (2 hours later)
> 
> [Orbital rings](http://www.orionsarm.com/fm_store/Paul%20Birch's%20Page.htm) and [Dyson spheres](http://www.aleph.se/Nada/dysonFAQ.html) are possibly good examples.
> 
> [Gravitational Balloons](http://gravitationalballoon.blogspot.com/) are also pretty cool, and might be more realistic than an O'Neil cylinder since they allow very thick radiation shielding, micrometeor protection, etc. without the kinds of structural limitations that a spinning object runs into.
> 
> Dyson spheres typically need to be more swarm like than solid structures. Contrary to Star Trek and other popular representations in fiction, they are a relatively poor candidate for a shellworld -- the gravitational physics don't work out well. DS's should be thought of more along the lines of a very high capacity power collector, which can feed lots of smaller colonies (and/or computronium for simulations, which is vastly more efficient than physical habitats). 
> 
> An interesting variant on the concept is the 'Dyson Bubble', which is supported by light pressure rather than orbital momentum, which gives greater flexibility in terms of the shape and so on. Such a structure would be engineered to be so lightweight that it would weigh about one large asteroid (2-Pallas) if it was positioned at 1.0 AU, or about a tenth that size at 0.3 AU. For heavier designs based on planetary disassembly, a spinning globe design would also be a possibility -- orbiting normally at the equator, with the poles being supported by the light pressure alone, and the hemispheric regions being partially light supported and partially orbiting. This would permit a fixed coordinate system between each point on the globe, while also letting you position the disassembled remains of Mercury in a ring.
> 
> If you do use a shellworld as a habitat, you will probably want a Gravitational Balloon (which exploit asteroid gravity to maintain their shape and pressurization) with a suitable engineering workaround for the lack of noticeable gravity on the inside. For example, you might have a bunch of small-ish plastic town-sized cylinders within a large zero-gee metropolitan structure. These would be powered to keep them spinning against air friction, possibly with a non spinning outer layer to prevent kicking up excessive wind currents. Another approach worth considering is genetic engineering to make humans tolerate zero-gee better, or cybernetics (bone surgery, etc.) that make its effects irrelevant.
> 
> Many of the 'structures' considered in the topic of megastructures aren't continuously connected physical objects, but swarms that are held in place by the dynamic activity of their components. Dyson spheres (aka dyson swarms) are one likely example of that. Orbital Rings (Birch Rings) are another possible example. A solid wire-like ring around the earth would have [stability issues](http://alnaspaceprogram.org/dynamic.html) as perturbations propagate along its length and pull it out of alignment. This might be damped out by building in shock absorbers, or it might turn out to be easier to use a swarm of millions of discrete pieces of ballast (perhaps with on-board magnetics and programming to continually nudge them into an optimal vector). Regardless of whether it is contiguous or not, the mass would be distributed relatively evenly in a ring *shape* that moves at slightly higher than orbital velocity, being kept closer to the earth than its natural orbit at that speed by the space elevator cables that it supports.
> 
> Economically speaking, orbital rings are a great example of a orbital launch capacity bootstrapping. You would boost a few thousand tons initially, then use the first ring to boost the materials needed to build additional rings (or beef up the original one). Eventually you end up with the capacity to launch materials at close to the cost in energy that it takes to get to orbit. Birch's papers note that you can launch a ring's mass in about 1/1000th of a year (about 8 hours). He extrapolates to 1000 times the initial mass in a year in his example, but if you were serious about growth you would actually double the ring mass once per 8 hours for 80 hours and wind up with 1024 times the original ring mass.
> 
> Dyson spheres are what happens when you get serious about collecting solar energy using self replicating robots. For example, a single robot unit gets set loose on the planet Mercury which uses solar energy to refine and launch materials to make additional solar panels. This results in the eventual disassembly of Mercury after a few decades, assuming the capacity of the robotic swarm doubles once per year. (If it doubles every month, the disassembly of the planet occurs much more rapidly than that.) The energy of the Sun is plenty for disassembling rocky bodies on the scale of Earth and smaller in a matter of a few days, but this ends up being a substantial bottleneck for things like disassembling Jupiter (which requires centuries using the full solar output). On the other hand, using full solar output (which is the result of around 4 million tons of mass converted per second) to generate laser energy focused on a small point should be more than enough to ignite fusion, or even create a [black hole](https://en.wikipedia.org/wiki/Black_hole_starship). So this might be best thought of as a mechanism to bootstrap even more dense power sources.
> 
> The economical story of Gravitational Balloons has to do with the benefits of population concentration and economies of scale. Materials strengths limit the size of spinning structures to some degree, but if you can work around that by putting lots of small spinning structures inside of one larger non-spinning structure, you get to exploit zero gravity for the sake of transportation between those structures. Even setting aside the physics of spinning, the shielding provided by the gravitational balloon can also be much thicker without costing as much materials per unit of volume, because the surface area of a very large structure tends to be much bigger per unit volume.

>> **u/None** [+3]  (10 hours later)
>> 
>> A dyson sphere doesn't require any new technology. It just required that we build lot and lot of satellites.
>> 
>> How we get there and how long it takes is up to us.

>> **u/Cuz_Im_TFK** [+3]  (a day later)
>> 
>> > using full solar output (which is the result of around 4 million tons of mass converted per second) to generate laser energy
>> 
>> This is called a Nicoll-Dyson Beam and, even with our own sun, would be powerful enough to vaporize pretty much anything in the galaxy given enough time. You can also use it to accelerate a relativistic kill missile by shining it on its mirrored "solar sails" if you'd rather blow something up via impact rather than vaporize it. It's so ridiculously powerful that there's not much use for it other than destruction, unless they really can create black holes and that turns out to be the best way of gathering some limited resource. 
>> 
>> On the other hand, if you don't go all the way to making it a laser, you can use hemispherical mirrored Dyson shells called Shkadov Thrusters to actually *move* stars (and drag their planetary systems along with them) which seems much more useful, especially if you want to move a star that will eventually supernova out of your galactic neighborhood.

>>> **u/lsparrish** [+4]  (a day later)
>>> 
>>> Nicoll-Dyson beam is when you use a Dyson sphere as a gigantic [phased array](http://www.radartutorial.eu/06.antennas/Phased%20Array%20Antenna.en.html), which is when you run multiple radio emitters in sync to produce a directional wave (laser, in the case of visible light) at the point where they add up. There are some efficiency issues with phased arrays (much of the energy is lost in side beams called grating lobes), but it might not be a problem in this context.
>>> 
>>> They are pretty versatile, as you can vary the intensity and deliver to any number of targets simultaneously. You could use one to make a black hole (which functions as a matter to energy converter), ignite fusion reactions on Jupiter, terraform iceballs throughout the Oort cloud, etc.
>>> 
>>> You could also focus the energy on disassembling the Sun (aka Star Lifting), to slow down its hydrogen consumption and permit use of its hydrogen throughout the solar system.

> **u/None** [+8]  (10 hours later)
> 
> [The megastructure series](https://www.youtube.com/playlist?list=PLIIOUpOge0LtW77TNvgrWWu5OC3EOwqxQ) by Isaac Arthur is a particularly good introduction to megastructure engineering. 
> 
> If he's familiar, you probably have seen his work submitted or mentioned a few times in this reddit, the latest being the topic of [stupid aliens.](https://www.youtube.com/watch?v=yXWe8g0zziw)

> **u/VorpalAuroch** [+4]  *Life before Death* (5 hours later)
> 
> Plot seed: there is a megastructure left behind by Inscructable Ancient Aliens for Inscrutable Ancient Reasons. They left the security on, so while it has advanced technology and possibly knowledge, it's also highly risky. For Reasons, the protagonist needs to get a package from point A to point B, and to evade detection has to pass through the megastructure.
> 
> TL;DR: Megastructure as [Fire Swamp](http://princessbride.wikia.com/wiki/Fire_Swamp).

> **u/Teal_Thanatos** [+4]  (3 days later)
> 
> the webcomic SchlockMercenary contains a megastructure called a buuthandi,  essentially a solar sail version of a dyson sphere.
> 
> http://schlockmercenary.wikia.com/wiki/Buuthandi

> **u/Teal_Thanatos** [+3]  (2 hours later)
> 
> the Judge Dredd Movie was almost entirely inside a single megastructure. The building almost assuredly counts, though it is at the lower end of spectrum, much like the Great wall of china.
> Though I won't rate the movie highly, it is something to show the unique challenges that stories in megastructures face and the advantages of having a story in a megastructure.

>> **u/Sailor_Vulcan** [+5]  *Champion of Justice and Reason* (3 hours later)
>> 
>> Kingdom Hearts: Chain of Memories does the same thing

> **u/VorpalAuroch** [+3]  *Life before Death* (8 hours later)
> 
> The one I find most intriguing is a [Topopolis](https://en.wikipedia.org/wiki/Topopolis) aka Cosmic Spaghetti. Many, many O'Neil half-cylinders in sequence, extending to connect up in arbitrarily-complex torus knots. Extremely dense knotting creates an interesting environment to embed the megascale equivalent of intricate city travel in.

> **u/Munchkingman** [+3]  (6 days later)
> 
> Just for posterity, one of my favorite megastructures is the manga Blame!'s (pronounced blam) "The City", a place built by building machines that were simply never turned off for millennia. It has a radius of at least 5AU, and the protagonist, at one point, walks across a room as large as Jupiter. He isn't really human.

> **u/Dr__Pi** [+2]  (a day later)
> 
> The note about Gravitational Balloons got me thinking - and this is purely speculation at this point - about a smaller-scale (possibly housing several thousand or tens of thousands) floating station/habitat.
> 
> The concept is to have a 'bubble' habitat for (likely flying/aerial) beings with sufficiently advanced technology to build a structure with e.g. a nanofibre weave to keep weight down.  (Beings which fly would have fewer infrastructural requirements, keeping the weight down further.)
> 
> The structure itself would be filled with their breathable atmosphere, which has a sufficient density differential with the upper atmosphere of a gas giant to stay afloat at some required altitude to have a comfortable gravitational force.  (The atmosphere would have to be very light e.g. helium; I need to research light atmospheres that could potentially be useful to the biological systems of life as we know it.)
> 
> I imagine it would also need at least six stabilizer engines to maintain the intended altitude and attitude given variable weight of the system and external pressures (e.g. winds).
> 
> My initial concerns are: 1) that gas giants can have extremely strong EM fields - is this true for most or all?  2) that the two different atmospheres (when combined with the weight of the habitat, determining its 'natural' altitude) and its orbital speed must all be balanced in order to find a comfortable gravitational force - is this possible?
> 
> What are your thoughts?  I do want to be very careful about realism when designing these kinds of things, but haven't researched anything yet.  I'm thinking about using this concept in one of the later books in a sci-fi series I'm working on that follows the development of an AI society after a human extinction event.
> 
> Thanks!

>> **u/Cuz_Im_TFK** [+2]  (a day later)
>> 
>> Regarding #1:
>> 
>> I think you typically *want* a strong EM field around your artificial habitats. It keeps you safe. Would the stronger EM field around a gas giant actually be disruptive to anything? Maybe telecommunications, but would it cause problems for anything locally? I could see it being an issue if the field was both really powerful and really chaotic, but if it's relatively stable, I don't see why it would cause a problem unless it's strong enough to affect the inhabitants biologically.

> **u/chaosmosis** [+2]  *and with strange aeons, even death may die* (a day later)
> 
> I read Awake In The Night Lands recently, and I kind of want to see a Last Redoubt story now.

> **u/khafra** [+1]  (6 days later)
> 
> Your second-to-last link had me thinking you were one of Charles Stross' nom de plumes; which honestly isn't that much of a stretch. You write real good.

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