One of the common features of an epic is the "fabulous loci" for the hero to visit. Fantasy novels can have some loci that are quite pretty or terrifying, but science fiction has some that will make your jaw hit the floor. Try comparing the land of Fairie with a ring around a sun with a radius of an entire astronomical unit and a livable surface area of three million times Terra.

Some of them are even from reality, e.g., Saturn's Rings.

Sargasso of Space

In old pulp science fiction there is a long history of taking a dramatic and comfortable metaphor and transporting it intact into the outer space environment. Generally the author has to savagely pound a square peg into a round hole, with regrettable results. The classic horrible example is deep space fighter aircraft.

Most pulp falls for the old Space Is An Ocean fallacy along with the related misconceptions.

Many pulp writers figured they were the first to have the bright idea of transplating the colorful legend of the dreaded Sargasso Sea into science fiction. A deadly area of space that somehow traps spaceships who venture too close, only to join the deadly graveyard of lost ships. And not just human ships, a couple stories mention humans discovering wrecks of unknown alien spacecraft mixed in with the conventional ships. The graveyard typically contains everything from recent ships all the way back to historical ships dating to the dawn of space flight.

Some stories populate the graveyard of dead ships with castaways. Who will probably be interested in looting your ship of any supplies it contains.

The original legend dates back to when line-of-sight was limited to the horizon, so a sailing vessel poking at the edge of the sargasso could not see the interior. Not without being caught, that is.

With the invention of radar and the realization that there ain't no horizon in space, writers realized they'd have to make the space sargasso sea more invisible. Usually they'd add on the legend of the Bermuda Triangle in the form of an intermittent "hole in space" leading to a pocket universe. Some kind of wormhole or stargate that would transport the hapless spacecraft to a graveyard of lost ships safely out of sight.

Obviously this is highly unlikely to happen in the real world. But it sure is romantic, in a sci-fi pulp fiction sort of way.

THE SARGASSO OF SPACE by Edmond Hamilton (1931)
The sargasso here is apparently the Neptune-Sol L5 point. Disabled spacecraft who drift into the point will be trapped, which is sort of true. The author does not explain why this is not true of the L4 and L5 points of every single planet in the solar system. He calls the graveyard of lost ships the "wreck-pack", and the gravitational attraction of the wrecks keep ships from drifting out.
CALLING CAPTAIN FUTURE by Edmond Hamilton (1940)
In this novel, the sargasso of space is created by ether-currents in the luminiferous aether. The latter is a concept that was disproved by Michelson and Morley in 1887, but most of the readers didn't know that. The ether-currents form sort of a one-way whirlpool which sucks hapless spacecraft into the graveyard of lost ships trapped in the eye of the storm. Captain Future escapes by cannibalizing engine and atomic fuel from the other derelict ships, an idea that apparently didn't occur to any of the prior castaways. He has a side adventure when he stumbles over an alien spacecraft full of aliens in suspended animation. The "adventure" part comes in when Captain Future discovers the octopoid creatures are space vampires and they start to wake up.
SARGASSO OF LOST STARSHIPS by Poul Anderson (1952)
Superstition says that the Black Nebula is haunted. Certainly strange things happen to hyperdrive starships who venture too close. Things like hallucinations, ghostly whispering voices ("Spaceman, go home. Turn back, adventurer. It is death."), electrical gear malfunctioning. Many dissappear, so prudent ship captains give the Nebula a wide berth. The cause of all this is an ancient race of Elf-like psionic aliens living on a planet near the Nebula's center.
SARGASSO OF LOST CITIES by James Blish (1953)
The spacegoing cities of CITIES IN FLIGHT gather in the sargasso for reasons that have less to do with physics and more with economics. The antigravity Okie cities are sort of the migrant laborers of the galaxy. The stellar currency is based on germanium, some idiot figure out how to synthesize it and inadvertenly obliterated the economy of the entire galaxy. Since everybody is now broke, the flying cities cluster in what is basically an interstellar hobo jungle.
SARGASSO OF SPACE by Andre Norton (1955)
The valiant free traders of the good ship Solar Queen obtain the trading rights to the dead planet with the cheery name "Limbo". When they visit they learn the planet has a still-working alien installation created by forerunners which can grab passing spacecraft and crash them onto the graveyard of lost ships. As it turns out a crime syndicate wants to utilize the installation for fun and profit, so hilarity ensues.
THE GRAVEYARD OF SPACE by Milton Lesser (1956)
The graveyard of space is a ball of dead spacecraft orbiting in the asteroid belt. Apparently it started as a small sphere of neutronium or other dense material. As derelict ships stuck to it by gravitational attraction the total gravity grew. It is only a menace to ships with broken engines or no fuel. The planetary governments keep talking about blasting it and salvaging the metal but can never agree on the details. Our heroes accidentally crash into it, breaking their Gormann series eighty radarscope. They cannot escape without one. So they start investigating the ships of the graveyard hoping to scavange a replacement. That's when they discover the hard way that anybody trapped in the graveyard will have to resort to cannibalism in order to survive, and who will treat them like the unexpected arrival of fresh meat on the hoof.
THE STARS MY DESTINATION by Alfred Bester (1956)
The protagonist Gulliver Foyle encounter the Sargasso Asteroid, a body in the main asteroid belt built entirely from the hulks of abandonned spaceships.
TIME TRAP episode of Star Trek Animated (1973)
The Starship Enterprise and a Klingon battle cruiser become trapped in the "Delta Triangle", an almost not disguised reference to the Bermuda Triangle. A hole in space drops them in to a pocket universe answering to a sargasso sea, and packed with the graveyard of lost starships. They find the centuries-old Starship Bonaventure, first starship with warp drive. But all the crew of all the ships are still alive, since people age slowly inside the sargasso, and antimatter lasts a long time. The Enterprise and the Klingon escape by hot-wiring their engines together, though true to form the dastardly Klingons try last minute treachery.
DRAGON'S DOMAIN epsiode of Space 1999 (1975)
In a flashback, Tony Cellini remembers when he was on the Ultra Probe to the newly discovered planet Ultra. Nearby they encounter a cluster of drifting abandoned alien ships. They discover why the ships are abandoned when an unconvincing octopoid monster with one eye and a firey maw materializes and starts to eat the crew.
THE METAMORPH epsiode of Space 1999 (1976)
Mentor of the planet Psychon needs to abduct sentient beings so he can drain their mental energy into his diabolical biological computer. He uses magnetic force to drag down to the planet any spacecraft that pass by, creating a large graveyard of lost ships nearby his operation.
DEADLY REUNION (Star Wars Comic) by Archie Goodwin (1981)
The Graveyard of Lost Ships was a collection of starships which were drawn into orbit around a collapsed dwarf star by Doctor Arakkus. The Graveyard consisted of five interconnected rings of ships all of which had been lured to the Graveyard with distress calls, in an attempt to make others suffer as he had suffered. The ships were trapped in the Graveyard by the gravitational pull of the dwarf star. Incapable of escaping its grasp, the ships slowly began to plunge into the star, while most of the crews went insane and committed suicide. But Han Solo, Luke Skywalker, and Chewbakka put a stop to this.
MÖBIUS DICK episode of Futurama (2011)
The Planet Express makes the mistake of taking a short-cut through the Bermuda Tetrahedron (an almost not disguised reference to the Bermuda Triangle) and land in a graveyard of lost spacecraft. The graveyard includes many media science fiction ships as joke references, including Discovery One from 2001 A Space Odyssey, Oceanic Airlines Flight 815 from Lost, the Satellite of Love from Mystery Science Theater 3000, the Jupiter II from Lost In Space, the ship from Josie and the Pussycats in Outer Space, the ship from the album covers of Electric Light Orchestra and Boston, an Apollo Lunar Module, an Apollo Command and Service Module, and Skylab.

      "The dead area," Crain told them, "is a region of space ninety thousand miles across within Neptune's orbit, in which the ordinary gravitational attractions of the solar system are dead. This is because in that region the pulls of the sun and the outer planets exactly balance each other. Because of that, anything in the dead-area, will stay in there until time ends, unless it has power of its own. Many wrecked space-ships have drifted into it at one time or another, none ever emerging; and it's believed that there is a great mass of wrecks somewhere in the area, drawn and held together by mutual attraction."
     "Wreck-pack in sight ahead!"
     "We've arrived, anyway!" Kent cried, as he and Crain hastened up into the pilot house. The crew was running to the deck-windows.
     "Right ahead there, about fifteen degrees left," Liggett told Kent and Crain, pointing. "Do you see it?"
     Kent stared; nodded. The wreck-pack was a distant, disk-like mass against the star-flecked heavens, a mass that glinted here and there in the feeble sunlight of space. It did not seem large, but, as they drifted steadily closer in the next hours, they saw that in reality the wreck-pack was tremendous, measuring at least fifty miles across.
     Its huge mass was a heterogeneous heap, composed mostly of countless cigar-like space-ships in all stages of wreckage. Some appeared smashed almost out of all recognizable shape, while others were, to all appearances unharmed. They floated together in this dense mass in space, crowded against one another by their mutual attraction.
     There seemed to be among them every type of ship known in the solar system, from small, swift mail-boats to big freighters. And, as they drifted nearer, the three in the pilot-house could see that around and between the ships of the wreck-pack floated much other matter—fragments of wreckage, meteors, small and large, and space-debris of every sort.
     "Lord, who'd have thought there were so many wrecks here!" Kent marvelled. "There must be thousands of them!"
     "They've been collecting here ever since the first interplanetary rocket-ships went forth," Crain reminded him. "Not only meteor-wrecked ships, but ships whose mechanisms went wrong—or that ran out of fuel like ours—or that were captured and sacked, and then set adrift by space-pirates."
     In those hours Kent and Crain and all in the ship watched with a fascinated interest that even knowledge of their own peril could not kill. They could see swift-lined passenger-ships of the Pluto and Neptune runs shouldering against small space-yachts with the insignia of Mars or Venus on their bows. Wrecked freighters from Saturn or Earth floated beside rotund grain-boats from Jupiter.
     The debris among the pack's wrecks was just as varied, holding fragments of metal, dark meteors of differing size—and many human bodies. Among these were some clad in the insulated space-suits, with their transparent glassite helmets. Kent wondered what wreck they had abandoned hastily in those suits, only to be swept with it into the dead-area, to die in their suits.

From THE SARGASSO OF SPACE by Edmond Hamilton (1931)

      Captain Future fought to break clear of this strong, invisible current, but the rocket-tubes seemed utterly powerless. At appalling speed, the space-boat was whirled through the void.
     He realized the terrible peril into which they had fled. Its nearness had been haunting him during all this time.
     "The cruiser has given up the pursuit!" Joan cried joyfully. "They're turning back – leaving us!"
     Captain Future's tanned face was grim. "They're doing so because they don't want to be trapped as we're trapped."
     "Trapped?" cried Kansu Kane. "What do you mean?"
     "We can't get out of this ether-current," Curt gritted. "It's too strong. And its whirling us on into the most dangerous spot in space, one from which no interplanetary ship has ever escaped."
     Joan's hand went to her throat. "You mean –" Captain Future nodded grimly.
     "Yes. We're being carried into the Sargasso Sea of Space."
     The Sargasso Sea of Space! The legendary, mysterious peril to navigation that was dreaded by every spacesailor in the System!
     Joan Randall's pretty face was pale and stricken, and little Kansu Kane stared bewilderedly, as Captain Future told them that their space-boat was being drawn into that deadly trap.
     The space-boat was still being carried at frightful speed through the void by the ether-current gripping it. The Legion of Doom cruiser, recoiling from the danger, had vanished.
     "It's my fault," Curt Newton said, his tanned face self-accusing. "I knew from the currents that we were getting near the Sargasso. But I thought I could escape it and shake off pursuit."
     "You were wonderful to get us out of that ship!" Joan cried loyally to the red-haired scientific wizard. "And you'll get us out of the Sargasso – I know you will."
     "What is this Sargasso of Space you're talking about?" Kansu Kane demanded. "I'm no space-sailor – I never heard of it."
     "You know what an ether-current is, don't you?" Captain Future asked him. "Well, there are many strong ether-currents, strange running tides in the luminiferous ether itself, out in this part of the System. They all flow into a central vortex, and anything that is carried into the vortex can't get out again, against the currents. That central vortex is the Sargasso Sea of Space."
     Curt reached for the throttles. "I'll try once more to break out of the current," he muttered. "But I'm afraid –"
     He opened the throttles to the limits. It was futile. The power was not enough to get them out of the remorseless grip of the ether-current that was sweeping them fatally on into a dreaded, unknown region of space.
     Captain Future shut off the rockets. "No go," be said, shaking his red head. "Might as well save our power, until we get into the central vortex. Then we'll see what we'll see."
     Clinging for support, they felt their craft batted about by titanic, unseen tides. Everything was topsy- turvy.
     Then, after terrifying minutes of chaotic movement, the space-boat seemed to enter smooth. undisturbed space. It floated now as placidly as though on a millpond.
     "Why, we're out of the currents now." Kansu Kane faltered, peering out with myopic eyes.
     "We've escaped from the Sargasso?" Joan cried joyfully to Captain Future.
     Curt shook his bead. "I'm sorry to disillusion you. We've reached the dead-center of the whirlpool of currents, an area of undisturbed space at the heart of this space-maelstrom."
     He opened the throttles, starting up the rockets. "We'll try to buck our way back out, but I'm pretty sure it's useless."
     Rockets flaming, the little boat shot back in the direction from which it had come. In a half-minute it plunged again into the titanic, invisible ether-currents. The currents grasped the craft once more and flung it like a toy back into the dead-center.
     "Thought so," Curt muttered. "We're in here to stay, unless we can devise enough new power to carry us out."
     "Where do you expect to find any additional source of power in this empty hole in space?" Kansu asked hopelessly.
     "There," said Captain Future quietly, pointing ahead.
     They stared. Far ahead, avast jumbled metal mass floated motionless in space. The mass was lenticular in shape, and hung at the very center of the dead-area here in the maelstrom.
     As their craft hummed closer, they saw that this farflung, jumbled mass was a great aggregation of space ships and debris of all descriptions. All this flotsam was held together by its own slight mutual gravitation.
     "What is it?" Joan Randall whispered awedly.
     "It is the graveyard of space ships," Curt said. "The last resting-place of every ship that has been sucked into the Sargasso Sea of Space since interplanetary travel began. No ship has ever escaped here – all that blundered in are still here."
     In the pack were space ships of every kind that had ever sailed the System. Great Jovian grain-boats, dumpy Martian freighters, streamlined liners from the Neptune and Uranus routes, black cruisers of the Planet Police, ominously armed pirate ships, even small spaceyachts. These dead ships floated, rubbing slowly against each other's sides. And between and among them floated all kinds of interplanetary debris that had been swept into the maelstrom – meteors large and small, fragments of splintered asteroids, bits of metal wreckage, and stiff, space-suited bodies of dead men who perhaps had floated in the void for years before drifting into this last resting place.
     Unutterably awe-inspiring was the sight, here in the thin, pale sunlight of outer space. Here was the end of many a brave-hearted voyage. Here many a good ship that had once throbbed from world to world had come to peace and quiet at last. Here was a Valhalla of space ships and space-men. whose eternal tranquility and silence would not be disturbed until the System ended.
     "Do you think there are any living people in those ships, Captain Future?" asked Joan Randall in a low voice.
     "I'm afraid there's no chance of that. The air-supply of any ship that drifted in here would soon be exhausted, and then any living people aboard would die."
     "Then we will perish when our boat's air-tanks are empty?' the girl cried. "Only two days from now?"
     "We're going to try to get out of here before then"' Curt said grimly. "There's just a chance that if we fitted up this space-boat with additional cyclotrons taken from some of these wrecks, it would give us enough power to fight out through the currents. We'll have to go through the wrecks first and see if we can find enough cyclotrons in good condition," he added.

     Curt stared. She was pointing at a strange object several ships away. It was a cylinder of blank gray metal several hundred feet long, without the lines of a ship at all.
     "I don't know – it's certainly no space ship of our System," Curt declared. "It may be from outside the System – a queer wreck out of interstellar space that drifted into the System and was caught here in the Sargasso." His gray eyes kindled with scientific interest. "We'll take a look. Come on, Joan."
     They started toward the enigmatic cylinder. But they stopped again, before they reached it. stricken with wonder by the appearance of the craft that floated next to it.
     This was a space ship of ridiculously small size and flimsy appearance. It was crudely designed, with projecting rocket-tubes of an ancient, inefficient type. The little vessel was the most antiquated and obsolete of any they had seen yet.
     "Why, it looks like one of the first space ships that was ever built!" Joan cried. "Could men ever have sailed space in a craft like that?"
     Curt's tanned face was suddenly tense and strange. "I've an idea I know what craft this is," he said. "Yes, I'm right-look at the name on its bows!" The name was Pioneer III.
     "Pioneer III?" cried Joan. "Why, that was the ship of Mark Carew, the first man ever to –"
     "The first man ever to sail beyond Jupiter," Captain Future finished softly, staring almost in reverence at the clumsy little craft. "Mark Carew, the second great trailblazer of space – the man who first visited Saturn and Uranus and Neptune, and who was lost in space in a later voyage. And this is where he was lost, here in the Sargasso."

(ed note: in other words a historical ship dating to the dawn of space flight)

     Next moment, he stiffened inside his space suit and heard a sharp cry from Joan. A door was opening in the cylinder.
     It opened like the iris shutter of a camera, expanding from a tiny aperture into a circular opening ten feet across.
     "What opened that door?" cried the girl, panic-stricken. "We weren't even near it."
     Curt's gray eyes flashed. "That door must be telepathically operated—when I wished a door would open, it opened!"

From CALLING CAPTAIN FUTURE by Edmond Hamilton (1940)

      Five years. Five years ago Barbara Jean Ramsey and their son Harold were due back from Meiji. Superstitiously, Bart had waited for them before accepting his promotion... Barbara Jean had never come home from Meiji. Her ship had taken a new direct route along an Alderson path just discovered. It never came out into normal space. A scoutcraft was sent to search for the liner, and Senator Grant (Barbara's father) had enough influence to send a frigate after that. Both vanished, and there weren’t any more ships to send.

     “You got five forces in this universe we know about, ja? Only one of them maybe really isn’t in this universe; we do not quibble about that, let the cosmologists worry. Now we look at two of those forces, we can forget the atomics and electromagnetics. Gravity and the Alderson force, these we look at. Now you think about the universe as flat like this table, eh?” He swept a pudgy hand across the roseteak surface. “And wherever you got a star, you got a hill that rises slowly, gets all the time steeper until you get near the star when it’s so steep you got a cliff. And you think of your ships like roller coasters. You get up on the hill, aim where you want to go, and pop on the hyperspace drivers. Bang, you are in a universe where the Alderson effect acts like gravity. You are rolling downhill, across the table, and up the side of the next hill, not using up much potential energy, so you are ready to go again somewhere else if you can get lined up right, O.K.?”
     Ramsey frowned. “It’s not quite what we learned as middies—you’ve got ships repelled from a star rather than—”
     “Ja, ja, plenty of quibble we can make if we want to. Now, Captain, how is it you get out of hyperspace when you want to?”
     “We don’t,” Ramsey said. “When we get close enough to a gravity source, the ship comes out into normal space whether we want it to or not.”
     Stirner nodded. “Ja. And you use your photon drivers to tun around in normal space where the stars are like wells, not hills, at least thinking about gravities. Now, suppose you try to shoot past one star to another, all in one jump?”
     “It doesn’t work,” Ramsey said. “You’d get caught in the gravity field of the in-between star. Besides, the Alderson paths don’t cross each other. They’re generated by stellar nuclear activities, and you can only travel along lines of equal flux. In practice that means almost line of sight with range limits, but they aren’t really straight lines. . . .”
     “Ja. O.K. That’s what I think is happening to them. I think there is a star between A-7820 and 82 Eridani, which is the improbable name Meiji’s sun is stuck with.”
     “Now wait a minute,” Admiral Torrin protested. “There can’t be a star there, Professor. There’s no question of missing it, not with our observations. Man, do you think the Navy didn’t look for it? A liner and an explorer class frigate vanished on that route. We looked, first thing we thought of.”
     “Suppose there is a star there but you are not seeing it?”
     “How could that be?” Torrin asked.
     “A Black Hole, Admiral. Ja,” Stirner continued triumphantly. “I think Senator Grant fell into a Black Hole.”

     “Then how would Black Holes interact with—oh,” Rap Torrin said, “gravity. It still has that.”
     Stirner’s round face bobbed in agreement. “Ja, ja, which is how we know is no black galaxy out there. Would be too much gravity. But there is plenty of room for a star. Now one thing I do not understand though, why the survey ship gets through, others do not. Maybe gravity changes for one of those things, ja?”
     “No, look, the Alderson path really isn’t a line of sight, it can shift slightly—maybe just enough!” Torrin spoke rapidly. “If the geometry were just right, then sometimes the Hole wouldn’t be in the way. . . .”
     “O.K.,” Stirner said. “I leave that up to you Navy boys. But you see what happens, the ship is taking sights or whatever you do when you are making a jump, the captain pushes the button, and maybe you come out in normal space near this Black Hole. Nothing to see anywhere around you. And no way to gets back home.”
     “Of course.” Ramsey stood, twisted his fingers excitedly. “The Alderson effect is generated by nuclear reactions. And the dark holes—”
     “Either got none of those, or the Alderson force stuff is caught inside the Black Hole like light and everything else. So you are coming home in normal space or you don’t come home at all.”

(ed note: in other words the ships fell into the interstellar Bermuda Triangle and are currently caught in the Sargasso Sea of Space)

     “Which is light-years. You’d never make it.” Ramsey found himself near the bar. Absently he poured a drink. “But in that case—the ships can sustain themselves a long time on their fuel!”
     “Yes.” Lermontov said it carefully. “It is at least possible that Senator Grant is alive. If his frigate dropped into normal space at a sufficient distance from the Black Hole so that it did not vanish down.”
     “Not only Martin,” Bart Ramsey said wonderingly. His heart pounded. “Barbara Jean. And Harold. They were on a Norden Lines luxury cruiser, only half the passenger berths taken. There should have been enough supplies and hydrogen to keep them going five years, Sergei. More than enough!”

(ed note: Spoiler: a rescue mission is sent. The only way to get back is to somehow generate a large nuclear reaction to create the Alderson effect. Crashing one of the trapped starships on the Black Hole will work. Unfortunately this is even more difficult that crashing a ship onto the Sun: the intense gravity will make the ship miss if you are a fraction of a degree off. Which means some brave volunteer will have to sacrifice themself to save the others, manually piloting the ship into a collision while the rescue ship is poised to jump. The rescue ship waits with their Alderson drive turned on, when the crashing ship creates the Alderson effect the drive will have something to make the ship jump.)

From HE FELL INTO A DARK HOLE by Jerry Pournelle (1973)

Spectacular Planets

When you are trying your hand at worldbuilding, please try to avoid ice planets, desert planets, swamp planets, farm planets, volcano planets, and other single-biome planets. The pejorative term for this mistake is Monocosm (term invented by Roz Kaveney). Jerry Pournelle parodied this trope with the phrase "It was raining on Mongo that morning"

Back in the 1950s nothing said "scifi" better than the ringed planet Saturn. One amusing variation is the planet Moth from The Tar Aiym Krang by Alan Dean Foster. Instead of having a full ring, it has two cresents on each side. This makes it look like the planet has wings.
The ultimate urban planet, with cities covering every square centimeter of land area (except for a few acres of Imperial Pleasure Gardens) including kilometer-high skyscrapers and kilometers of underground levels for the morlocks.

The most famous is the planet Trantor from Isaac Asimov's Foundation trilogy (but given a much more detailed description in Donald Kingsbury's pastiche Psychohistorical Crisis). Trantor is famous among those literate in science fiction, the SF illiterates are familiar with the concept mostly from the planet Coruscant from the Star Wars series of movies.
This is a famous bit of worldbuilding from the novel Mission Of Gravity by Hal Clement. The only planet in the 61 Cygni system, Mesklin's surface gravity varies from 3 gees at the equator to an outrageous 700 gees at the poles. The variation is due to the ultra-high rotation rate, it spins at twenty degrees a minute making the day some seventeen and three quarter minutes long.
This is a dumbbell-shaped double planet which are so close together that they share a common atmosphere. It is possible to fly from one planet to another with an aircraft.
These planets were the result of some worldbuilding for the ill fated "Twayne Triplet" series of science fiction novels. Uller is a planet containing silicon life while Niflheim's atmosphere contained dangerous amounts of the hideously corrosive gas fluorine.
In this allegorical story, the main planet of Alpha Virginis has a gynecomorphous mountain range called the Virgin. It is a plateau about ten thousand feet above sea level, and it looks exactly like a titanic sculpture of a nude woman in repose with lakes for eyes. (Goddess in Granite by Robert Young)
The planet has a Venus-like uninhabitable atmospheric pressure. Except for the unreasonably tall (40 kilometers) plateau Mount Lookitthat. It has habitable atmospheric pressure, a pity the surface area is only half that of California. (A Gift From Earth by Larry Niven)
Sort of the opposite of Plateau, the atmosphere is too thin for humans. A weapon called the "Wunderland Treatymaker" gouged out a long kilometer deep canyon with a size about equal to the Baja California peninsula. Air pressure at the bottom of the canyon is suitable for humans. (The Ringworld Engineers by Larry Niven)
The planet is not spherical, it is a prolate spheroid. The poles actually rise out of the amosphere in to vacuum, the atmospheric pressure at the equator is too high for human habitation, the intermediate regions are suitable for humans. (World of Ptavvs, Borderland of Sol by Larry Niven)
This is a torus (donut shape) composed of breathable gases with a jaw-dropping radius of 26,000 kilometers, about four times the radius of Terra. The smoke ring is created by a gas giant called Goldblatt's World which apparently is mostly oxygen instead of hydrogen as is usual. Goldblatt is orbiting a neutron star named Voy, just outside the Roche limit. Which means Goldblatt is constantly shedding its atmosphere to replenish the smoke ring.

There is a wide variety of life living in the free fall environment of the smoke ring, including a colony of humans. There are even aquatic creatures living in huge spherical floating ponds. (The Integral Trees, The Smoke Ring by Larry Niven)

Thundering Worlds

If you are fixated on the concept of "bigger is better," then it is hard to beat the idea of a spaceship the size of a planet. Or a planet converted into a spaceship.

Well, maybe if you converted a Ringworld into a Bussard Ramjet to make a starship one astronomical unit in radius. That would be bigger.

Hang on, you could turn a star into a Shkadov thruster and turn an entire freaking solar system into a spaceship. Please pardon me, I have to go lie down a minute, my head hurts.

Please note that in our galaxy there are some real stars that are moving unusually fast.

Runaway stars are clipping along at around 100 kilometers per second. They are thought to be binary stars which passed too close to another star so one star got sling-shotted out. Or one star of a binary star system where the other blew up in a supernova. For science fictional purposes some sinister alien race converted their sun into a Shkadov thruster so they could go cruising for trouble.

A good example is Barnard's Star aka "Barnard's Runaway Star" or "Greyhound of the Skies". Astronomers measured the lateral speed and the radial velocity to calculate a space velocity of 142 km/s which is smokin'. And it is only 1.8 parsecs away (5.98 light-years), making it the fourth-closest star to the Sun. Jack Williamson used this in his novel The Legion of Space, home of the dreaded giant jellyfish-like Medusae who drive their solar system like a rocketship to invade innocent planets.

Hypervelocity stars on the other hand are screaming along like the proverbial bat-outta-hell. They move at about 1,000 km/s, which is quite a bit more than the galaxy's escape velocity. They are thought to have been sling-shotted by the Sagittarius A* supermassive black hole at the center of the galaxy. For science fictional purposes they are Shkadov thruster stars with the pedal to the metal, doing their best to get the heck outta Dodge ASAP. The important plot question being: what do they know that we don't? Apparently there is some awful thing that terrifies a civilization powerful enough to thrust their entire solar system up to a thousand klicks a second.


(ed note: Bussard Ramjet pilot Corbett was sent by The State totalitarian regime on an interstellar trip, but he goes his own way. Later he comes back to Terra after a relativistic trip lasting a few hundred millennia. He notices many small changes, such as the sun is burning hotter and Terra is now orbiting Jupiter. The State seems to have died out, replaced by two genetically engineered factions called the Boys and the Girls.)

      "Watch the show.”
     Certain stars glowed more brightly than others… and planetary systems circled them, greatly enlarged for effect. Now all but two of these systems turned sullen red—turned enemy. These were the worlds that had turned against the State.
     One of the red systems sparkled and faded into the background, its colony destroyed.
     The two neutral systems went red.
     Another system faded out.
     The view closed on Sol system… on more of Sol system than Corbell had known, with three dark gas giants beyond Pluto, and countless swarming comets.
     Fleets of spacecraft moved out toward the renegade colonies. Other fleets invaded. Sometimes they came like a hornet’s nest, many ships clustered around a Bussard ramjet core. Sometimes like a Portuguese man-of-war: thousands of ships as weights around the fringe of a great silver light-sail. Early fleets included hospital ships and return fuel; later there were massive suicide attacks.
     It went on for centuries. The State utopia became a subsistence civilization, turning all its surplus energy to war. The fleets moved at just less than lightspeed. News of success or failure or need for reinforcements moved barely faster. The State was Boys and Girls and dictators all united for the common good. Corbell hurt with the loss of that unity.

     He watched a beam of light bathe Sol system: laser cannon firing from Farside colony. Farside launched warships by light-sail at terrific accelerations. The ships dropped their sails and decelerated most of the way to Sol, arriving just behind the beam itself, long before the State could prepare. Corbell squirmed in his chair; he wanted to cry warning. For the State beat the invaders back, but failed to stop their hidden treachery.
     The war continued. Farside, economically ruined by its effort, fell before the counterattack. It took a man’s lifetime… too much time, before Astronomy noticed what the Farside traitors had done in the dark outside their dazzling light beam, in the distraction provided by the invasion.
     The State had looked for the light of fusion spacecraft, not the dim watery light of a new planet. The trans-Plutonian planet called Persephone had had a peculiar orbit, tilted nearly vertical to the plane of the solar system. Its new path had already taken it deep into the system.
     10 to the power 23 tons of hydrogen and hydrogen-compound ices were aimed to strike the sun at solar-escape velocity. Earth’s oceans would boil…

     The State did what it could. Tens of thousands of fusion bombs, Sol system’s entire armory, were set off at the dawn side of Persephone, just above the atmosphere. A thick rind of the planet’s atmosphere peeled away and streamed off like a comet’s tail, its mass pulling at Persephone’s dense core. A streamer of gas far more massive than the Earth broke free, and rounded the sun, and sprayed back toward the cometary halo.
     If the bombs could have been placed earlier, Persephone’s core would have done the same. It was rock and iron, yellow-hot, and it glowed X-ray hot as it streaked into the solar photosphere and disappeared.

     The sun grew bright.

     Oceans shrank, crops withered, tens of millions died before the State could place a disk of reflecting tinsel between Earth and Sol. It was a temporary measure. The sun’s new heat was permanent, at least on the human scale of time. Fusion would run faster in Sol’s hotter interior. The buried heat would leak to the photosphere and out.

     The State had one chance for survival. It could move the Earth by the method Farside had used to stop Persephone cold in its orbit.
     The State had had to abandon the Mercury mines: a serious industrial handicap. Nonetheless they were building something out there in the asteroid belt—something huge, like a starship big enough to carry the whole human race to safety. But no, that wasn’t it. Corbell was fascinated. He knew it might be the memory RNA, but he was fascinated anyway. He hardly heard what Skatholtz was saying: “It was sensible, Corbell. The Girls who made the light show ruled the sky. You are familiar with such things. Do you know now who hurled a moon at us?”
     “Not yet. Shut up and let me…”
     They had finished the thing. Two tubes, concentric, each a hundred miles long; the inner tube a mile wide, with thick walls of complex construction; the outer tube thinner and twice as wide. At one end, a bell-shaped rocket nozzle. At the other… Corbell knew more than he was seeing. Reworked military laser cannon, and vents, and a flared skirt, and thick stubby fins, there at the bottom end. Now temporary liquid hydrogen tanks were attached. Now the structure moved under its own power… it was a tremendous fusion motor… moving outward, circled by tiny ships… yeah.

     Corbell said, “How do you climb down off an elephant?”
     “Should I know that?”
     “You don’t climb down off an elephant. You climb down off a duck.” (1950s era grade-school joke. No, it wasn't funny back then either)
     “It’s so much safer. How do you move the Earth?
     Small wonder if the light show meant little to Skatholtz. Watching the construction of the motor—in the naked sunlight and sharp-edged, totally black shadows of space—was bewildering. The diagrams made sense to an architect, but they were only rotating lines to Skatholtz. But without bottled memory and without Corbell’s career in space, Skatholtz was still bright enough to makesome sense of what he was seeing.

     “You move something else,” Skatholtz said. “The damage done by the rocket’s thrust and by mistakes you might make will not kill anyone if nobody lives on the working body. Then the working body can be moved until the world falls toward it as a rock falls to the ground. What was the working body? Ganymede?”
     “Uranus. Can you stop the light show at that picture?”
     The lecture froze on an “artist’s conception”: a blurred, curved arc of Uranus’s upper atmosphere. The motor looked tiny floating there. Corbell said, “You see? It’s a double-walled tube, very strong under expansion shock. It floats vertical in the upper air. Vents at the bottom let in the air, which is hydrogen and methane and ammonia, hydrogen compounds, like the air that the sun burns. You fire laser cannon up along the axis of the motor, using a… color hydrogen won’t let through (light frequency that hydrogen absorbs). You get a fusion explosion along the axis.
     “I don’t understand all your words. Fusion?”
     “Fusion is the way a star burns. You probably used fusion bombs against the Girls.”
     “Okay. The hydrogen fusions in the middle of the motor—
     “—and the explosion goes out and up. It’s hottest along the axis, cooler when it reaches the walls of the motor. The whole mass blasts out the top, through the flared end. It has to have an exhaust velocity way higher than Uranus’s escape velocity. The motor goes smashing down into deeper air. You see there’s a kind of flared skirt at the bottom. The deep air builds up there at terrific pressure, stops the tube and blasts it back up. You fire it again.

     “Elegant,” said Skatholtz.
     “Yeah. Nobody’s there to get killed. Control systems in orbit. The atmosphere is fuel and shock absorber both—and the planet is mostly atmosphere. Even when it’s off the motor floats high for awhile, because it’s full of hot hydrogen compounds. If you let it cool off it sinks, of course, but you can bring it back up to high atmosphere by heating the tube with the laser, firing it almost to fusion. Start the light show again, will you?”
     Skatholtz barked something at Krayhayft. Corbell watched: Earth held out, barely. Heat-superconducting cables had to be run to the north polar cap to borrow its cold. The cap melted.
     Millions died anyway. No children were born; there wasn’t shelter for them. It took over a century to drop Uranus into place, six million miles ahead of the Earth in Earth’s orbit. The planet accelerated slowly, drawing Earth after it… and then sped up, to leave Earth behind, in a wider orbit. They lost the Moon.
     The sun expanded via its own internal heat. Light was reddened, but the greater surface lost more heat to space… to Earth. By now the Girls had charge of Uranus and the floating fusion motor. They moved the Earth again.
     Five times the Earth had to be moved. At one time it was circling precisely opposite Mars. Later, further out. Internally Sol’s fusion furnace had stabilized; but the photosphere was still growing. And the Earth must be moved a sixth time.

From A WORLD OUT OF TIME by Larry Niven (1976)

(ed note: the protagonist Louis Wu has been "hired" by an alien of the species Pierson Puppeteer to pilot a mission to a megastructure called a Ringworld. But first they have to stop at the Puppetter homeworld.)

     The pilot’s cabin was crowded. Louis hunched over the instrument panel, protecting buttons from the puppeteer’s careless hooves.
     “Spectroanalysis … yes. Now the blue-and-yellow double at two o’clock …
     “I have my bearings. Swing to 348, 72.”
     “What exactly am I looking for, Nessus? A cluster of fusion flames? No, you’d be using thrusters.”
     “You must use the scope. When you see it, you will know.”
     On the scope screen was a sprinkling of anonymous stars. Louis ran the magnification up until … “Five dots in a regular pentagon. Right?”
     “That is our destination.”
     “Good. Let me check the distance. — Tanj! (expletive. Acronym for There Ain't No Justice) That’s wrong, Nessus. They’re too far away.”
     No comment.
     “Well, they couldn’t be ships, even if the distance meter isn’t working. The puppeteer fleet must be moving at just under lightspeed. We’d see the motion.”
     Five dim stars, in a regular pentagon. They were a fifth of a light year distant and quite invisible to the naked eye. At present scope magnification they would have to be full sized planets. In the scope screen one was faintly less blue, faintly dimmer than the others.

     A Kemplerer rosette (sic. Should be Klemperer). How very odd.
     Take three or more equal masses. Set them at the points of an equilateral polygon and give them equal angular velocities about their center of mass.
     Then the figure has stable equilibrium. The orbits of the masses may be circular or elliptical. Another mass may occupy the center of mass of the figure, or the center of mass may be empty. It doesn’t matter. The figure is stable, like a pair of Trojan points.
     The difficulty is that there are several easy ways in which a mass can be captured by a Trojan point. (Consider the Trojan asteroids in Jupiter’s orbit.) But there is no easy way for five masses to fall accidentally into a Kemplerer rosette.

     “That’s wild,” Louis murmured. “Unique. Nobody’s ever found a Kemplerer rosette …” He let it trail off.
     Here between the stars, what could be lighting those objects?
     “Oh, no you don’t,” said Louis Wu. “You’ll never make me believe it. What kind of an idiot do you take me for?”
     “What is it that you will not believe?”
     “You know tanj well what I won’t believe!” (that the Puppeteers created the rosette)
     “As you please. That is our destination, Louis. If you will take us within range, a ship will be sent to match our velocity.”
     The rendezvous ship was a #3 hull, a cylinder with rounded ends and a flattened belly, painted shocking pink, and windowless. There were no engine apertures. The engines must be reactionless thrusters of the human type, or something more advanced.
     On Nessus’s orders Louis had let the other ship do the maneuvering. The Long Shot, on fusion drives alone, would have required months to match velocities with the puppeteer “fleet”. The puppeteer ship had done it in less than an hour, blinking into existence alongside the Long Shot with her access tube already reaching like a glass snake toward the Long Shot’s airlock.

     In the airlock the kzin stopped, suddenly caught by the sight of an expanding pentagon of stars.
     He could hardly have had a better view.
     The Long Shot, edging close in hyperdrive, had stopped half a light-hour ahead of the puppeteer “fleet”: something less than the average distance between Earth and Jupiter. But the “fleet” was moving at terrible speed, falling just behind its own light, so that the light which reached the Long Shot came from much further away. When the Long Shot stopped the rosette had been too small to see. It had been barely visible when Teela left the lock. Now it was impressively large, and growing at enormous speed.
     Five pale blue dots in a pentagon, spreading across the sky, growing, spreading …
     For a flashing instant there were five worlds around the Long Shot. Then they were gone, not fading but gone, their receding light reddened to invisibility.

     “Of course not,” said the puppeteer. “Doubtless you have been wondering about —”
     “Flying worlds,” the kzin interrupted.
     “And Kemplerer rosettes,” said Louis. “Okay, speak to us. Why flying worlds? Somehow it doesn’t seem safe to throw habitable worlds about with such gay abandon.
     “Oh, but it is, Louis!” The puppeteer was terribly earnest. “Much safer than this craft, for instance; and this craft is very safe compared to most human-designed craft. We have had much practice in the moving of worlds.
     “Practice! How did that happen?”
     “To explain this, I must speak of heat … and of population control. You will not be embarrassed or offended?”…

     …“But it does relate, Speaker. Half a trillion civilized beings produce a good deal of heat as a byproduct of their civilization. We had long since run out of farming land, and had been forced to terraform two worlds of our system for agriculture. For this it was necessary to move them closer to our sun.”
     “Your first experience in moving worlds. You used robot ships, of course.”
     “Of course … After that, food was not a problem. Living space was not a problem. We built high even then, and we like each other’s company.”…
     …“Our sole and only problem, at the time of which I speak, was heat.”
     “Heat is produced as a waste product of civilization.”
     “I fail to understand,” said Speaker-To-Animals.
     “An example. You would wish a light source at night, would you not, Speaker? Without a light source you must sleep, whether or not you have better things to do.”
     “This is elementary.”
     “Assume that your light source is perfect, that is, it gives off radiation only in the spectra visible to kzinti. Nonetheless, all light which does not escape through the window will be absorbed by walls and furniture. It will become randomized heat.
     “Another example. Earth produces too little natural fresh water for its eighteen billions. Salt water must be distilled through fusion. This produces heat. But our world, so much more crowded, would die in a day without the distilling plants.
     “A third example. Transportation involving changes in velocity always produces heat. Spacecraft filled with grain from the agricultural worlds produce heat on reentry and distribute it through our atmosphere. They produce more heat on takeoff.”
     “But cooling systems —”
     “Most kinds of cooling systems only pump heat around, and produce more heat for power.”
     “U-u-urr. I begin to understand. The more puppeteers, the more heat is produced.”
     “Do you understand, then, that the heat of our civilization was making our world uninhabitable?”

     “Incredible,” said Speaker-To-Animals. “Why didn’t you leave?”
     “Who would trust his life to the many deaths of space? Only such a one as me. Should we settle worlds with our insane?”…
     …They were of equal size: perhaps twice the angular diameter of the full Moon as seen from Earth. They formed a pentagram. Four of the worlds were circled by strings of tiny, glaring lights: orbital suns giving off artificial yellow-white sunlight. These four were alike in brightness and appearance: misty blue spheres, their continental outlines invisible at this distance. But the fifth …
     The fifth world had no orbital lights. It glowed by its own light, in patches the shapes of continents and the colors of sunlight. Between the patches was a black that matched the black of surrounding space; and this black, too, was filled with stars. The black of space seemed to encroach on continents of sunlight.
     “Incredible,” said Speaker-To-Animals. “I hardly dared believe it. You took your worlds with you.”
     “Puppeteers don’t trust spacecraft,” Louis said absently.…

     “But how?”
     “I had explained,” said Nessus, “that our civilization was dying in its own waste heat. Total conversion of energy had rid us of all waste products of civilization, save that one. We had no choice but to move our world outward from its primary.”
     “Was that not dangerous?”
     “Very. Then was much madness that year. For that reason it is famous in our history. But we had purchased a reactionless, inertialess drive from the Outsiders. You may guess their price. We are still paying in installments. We had moved two agricultural worlds; we had experimented with other, useless worlds of our system, using the Outsider drive. In any case, we did it. We moved our world.
     “In later millenia our numbers reached a full trillion. The dearth of natural sunlight had made it necessary to light our streets during the day, producing more heat. Our sun was misbehaving.
     “In short, we found that a sun was a liability rather than an asset. We moved our world to a tenth of a light year’s distance, keeping the primary only as an anchor. We needed the farming worlds and it would have been dangerous to let our world wander randomly through space. Otherwise we would not have needed a sun at all.”…
     …“Yes. Shortly after we finished moving our world, our sun began the process of expansion. Your fathers were still using the upper thigh bone of an antelope to crack skulls. When you began to wonder where our world was, you were searching the wrong orbits, about the wrong Suns.
     “We had brought suitable worlds from nearby systems, increasing our agricultural worlds to four and setting them in a Kemplerer rosette. It was necessary to move them all when the sun began to expand, and to supply them with sources of ultraviolet to compensate for the reddened radiation. You will understand that when the time came to abandon galaxy (when Beowulf Shaeffer discovered the galactic core was undergoing an explosion that would eventually sterilize the entire Milky Way), two hundred years ago, we were well prepared. We had had practice in moving worlds.”

From RINGWORLD by Larry Niven (1970)

      Runaway sun! Red, feeble, dying dwarf. Racing north­ward out of the constellation Ophiuchus, in mad flight from the Serpent and the Scorpion. Long ago christened "Barnard's Runaway Star," from its discoverer and its remarkable proper motion, it was the nearest star of the northern sky and the nearest found to have a habitable planet.
     "Please don't think I planned it, John! But the Medusae have tricked Eric—and the rest of us, it seems. They bargained to help us restore the Empire, in return for a shipload of iron. Now it seems they intend taking a good deal more."
     His gaunt frame shuddered.
     "They told me more of their history, just now, than Eric ever learned—and it's quite a history. They're old, John. Their sun is old. Their race was old, on that ghastly planet, before our Earth was ever born. They're too old, John—but they don't intend to die.
     "The remarkable motion of Barnard's Star, they tell me now, is a thing of their own accomplishment. Because the mineral resources of their own planet were used up long ago, they've arranged to visit others. In their career across the Galaxy, they live by looting the worlds they pass, and sometimes plant a colony—that's to be the fate of Earth, they tell me."
     He shook his white head with a sick, slow motion.
     "Please, John," he whispered, "don't think I ever intended that!"
     John Star and Jay Kalam stood voiceless with shock. The thing was unthinkable, but John Star knew it must be true. Reason insisted that the Medusae would scarcely join an interstellar war for a single cargo of iron. And Adam Ulnar's horrified remorse appeared sincere enough.
     Dazed, John Star pictured the doom of humanity. The System couldn't fight a science that built these black spider-ships of space and armed them with atomic suns for weapons; a science that fortified a planet with a belt of artificial satellites, and guided a star itself like a red corsair across the Galaxy.

From THE LEGION OF SPACE by Jack Williamson (1934)




Stellar scale

Most stellar scale Megastructure proposals are designs to make use of the energy from a sun-like star while possibly still providing gravity or other attributes that would make it attractive for an advanced civilization.

  • The Alderson disk is a theoretical structure in the shape of a disk, where the outer radius is equivalent to the orbit of Mars or Jupiter and the thickness is several thousand miles. A civilization could live on either side, held by the gravity of the disk and still receive sunlight from a star bobbing up and down in the middle of the disk.
  • A Dyson sphere (also known as a Dyson Shell) refers to a structure or mass of orbiting objects that completely surrounds a star to make full use of its solar energy.
  • A Matrioshka brain is a collection of multiple Concentric Dyson Spheres which make use of different wavelengths of light.
  • A Stellar engine either uses the temperature difference between a star and interstellar space to extract energy or serves as a Shkadov thruster.
  • A Shkadov thruster accelerates an entire star through space by selectively reflecting or absorbing light on one side of it.
  • Topopolis (also known as Cosmic Spaghetti) is a large tube that rotates to provide artificial gravity.

Planetary scale

  • An Orbital is a space habitat similar to but much smaller than a Niven Ring. Instead of being centered on a star, it is orbiting a star, thus its diameter is typically on the order of magnitude of a planet. By giving a tilt to its orbit, there's a convenient day and night experience on its surface.
  • Globus Cassus is a hypothetical proposed project for the transformation of Planet Earth into a much bigger, hollow, artificial world with the ecosphere on its inner surface. This model serves as a tool to understand the World's real functioning processes.
  • Butt nine is Buckminster Fuller's proposal for a tensegrity sphere of size a mile in radius which would be large enough so that it would float in the sky if heated by only one degree above ambient temperature, creating habitats for mini cities of thousands of people in each "Butt Nine".

Orbital structures

  • Orbital ring is an enclosed loop slightly larger than the circumference of the Earth so that it can maintain low earth orbit.
  • The Bernal sphere is a proposal for a space colony with a maximum diameter of 16 kilometers.
  • The Stanford torus is a different design with a diameter just under 1.7 kilometers.
  • The O'Neill cylinder is yet another space colony proposal.


Stellar scale

  • The Dyson shell (including its variation, the ringworld) has appeared in many works of fiction, including the Star Trek universe.
  • Larry Niven's series of novels beginning with Ringworld centered on, and originated the concept of a ringworld, or Niven ring. A ringworld is an artificial ring with a radius roughly equal to the radius of the Earth's orbit (1 AU). A star is present in the center and the ring spins to create g-forces, with inner walls to hold in the atmosphere. The structure is unstable, and required the author to include workarounds in subsequent novels set on it.
  • In the manga Blame! the Megastructure is a vast and chaotic complex of metal, concrete, stone, etc., that covers the Earth and assimilates the Moon, and eventually expands to encompass a volume greater than the orbit of Jupiter.
  • In White Light by William Barton and Michael Capobianco, a Topopolis is presented as taking over the entire universe.
  • In the Heechee books by Frederik Pohl the race of pure energy beings called The Foe have constructed the Kugelblitz, a black hole made of energy and not matter.
  • In the Xeelee series of books by Stephen Baxter, the eponymous alien race constructed the Ring, a megastructure made of cosmic strings, spanning over 10 million light years.
  • In Freelancer, The Dom'Kavosh's Dyson shell that is inhabited by a drone race created by the Dom'Kavosh, Nomads. This is reached via a hyper gate, created by the same creators as the Dyson sphere.
  • The Saga of Cuckoo series novel Wall Around a Star mentions a proposal to build a super dyson sphere, completely enclosing the Galactic Center.
  • The title of the novel Helix by Eric Brown directly references a stellar-scale helical megastructure. Different types of environments and habitats are interspersed along the structure, while their varying distance from the central star affects the climate.
  • The Quarg in the game Endless Sky are shown building a massive ring around one of their stars, which is most likely around one astronomical unit in diameter. A completed version of this can also be found in another location.
  • In Space Empires 4 and 5, the player can construct sphereworlds and ringworlds around stars.

Planetary scale

  • Several structures from the fictional Halo universe:
    • The original twelve Halos, seen in Halo: Cryptum, were 30,000 kilometers in diameter; a separate array of six Halos are 10,000 kilometers in diameter, with one of the original twelve later being reduced to this size in Halo: Primordium.
    • The Ark is a 127,530 km diameter structure from which the Halo Array can be activated and capable of building 10,000 km Halos. The "greater" Ark, seen in Cryptum and Primordium, is capable of producing 30,000 km Halos.
    • Onyx is an artificial planet made entirely out of Forerunner Sentinels (advanced replicating robots). At its core is a "shield world", contained within slipstream space, that is approximately one astronomical unit in diameter. The much smaller Shield World 0459, (approximately 1,400 km in diameter), is the setting for the latter half of Halo Wars. A third shield world, Requiem, is the primary setting for Halo 4. Requiem is an artificial hollow planet encased in a kind of Dyson Sphere.
    • High Charity, the Covenant's mobile planetoid station
  • Death Star from Star Wars
  • In Sonic Adventure 2 and Shadow The Hedgehog, the Eclipse Cannon is a WMD built inside of the Space Colony Ark. It fires a laser so strong that it can destroy planets and pierce stars. The Eclipse Cannon can't work on its own, and requires at least one Chaos Emerald for it to be functional. Even with only a few Chaos Emeralds powering it, it is still capable of destroying entire cities.
  • Buster Machine III from Gunbuster.
  • Culture Orbital
  • In the 2013 CGI anime movie, Space Pirate Captain Harlock, the Jovian Accelerator is an ancient, Death Star-like Weapon of mass destruction that uses energy from Jupiter's atmosphere to create a large beam of intense light strong enough to destroy an entire planet.
  • Trantor, the capital of an interstellar empire in Isaac Asimov's Foundation series, is an ecumenopolis, a planet entirely covered in one huge metal clad building, with only one small green space: the Emperor's palace grounds.
  • Coruscant, capital city in the Star Wars universe, entirely covers its host planet. It serves as capital of first the Republic and then later the First Galactic Empire.
  • The Galaxy Gun from the Star Wars universe, a large space station designed to destroy entire planets from across the galaxy could be considered a megastructure because its size is more than seven kilometers long.
  • The Centerpoint Station, from the Star Wars universe, a 350 km spherical space station at the Lagrangian point between the planets Talus and Tralus in the Corellia system. It was a gigantic and ancient hyperspace tractor beam with which an ancient race, known as Celestials, created the Corellia star system. With the help of the tractor beam whole planets could be moved through hyperspace and arranged into their actual orbits acound the central star. On the other hand, the same technology could be used as weapon to destroy even stars. On the inside of the main sphere a huge living space called Hollowtown was home to many people in similar fashion as on the inside of a dyson sphere.
  • The Ori Supergate seen in a number of episodes of Stargate SG1 could be classed as a megastructure
  • In The Hitchhiker's Guide to the Galaxy series, Earth, as well as other planets, were artificial megastructures. Earth was intended to function as a gigantic computer, and was built by a race of beings who made their living by manufacturing other planets.
  • The Star Forge from Star Wars: Knights of the Old Republic
  • Mata-Nui in the BIONICLE franchise is classifiable as a megastructre. In the story he is a massive robot as tall as a planet, and inside his body, every inhabitant of the BIONICLE Universe (Matoran, Toa, etc.) all live, unaware that they live inside a massive, space-traveling entity.
  • In the Robotech Sentinels novels, Haydon IV is an artificially constructed cyber-planet with android citizens.
  • In the Invader Zim episode "Planet Jackers", two aliens surround the Earth with a fake sky in order to throw it into their sun.
  • Nightmare's fortress from Kirby: Right Back at Ya! can be classified as a megastructure because it's the size of a small planet.
  • In several works, Arthur C. Clarke writes about a colossal hollow tube, first described in Rendezvous with Rama (1973), and inhabited by different races.
  • The Citadel in the Mass Effect universe is an enormous space station constructed by an ancient race of machines called the Reapers millions of years before the games in the series. At the time of Mass Effect 2, its population is 13.2 million.
  • In the game Airforce Delta Strike a large Space Elevator called the Chiron Lift is used to send supplies out into outer space.
  • In the Warhammer 40,000 series, the Imperial Palace (site of the Golden Throne wherein the Emperor of Mankind is kept alive indefinitely) could be considered a megastructure. The palace is a complex of continent-wide structures with the Golden Throne being located in an area stretching across the whole of the Himalayan mountains.
  • In the film Elysium, a luxury space station (a Stanford Torus) called Elysium houses the wealthy population of the human species.

Megascale structures

Structures that might not be classified as "Megastructures" because they do not meet the requirements, but are indeed "Mega" sized structures/constructions.

Stellar scale

From the Wikipedia entry for MEGASTRUCTURE


     Robert Heinlein’s early story “Universe” has been imitated countless times by most of the writers in the business.
     The idea was this: Present-day physics poses a limit on the speed of an interstellar vehicle. The ships we send to distant stats will be on one-way journeys, at least at first. They will have to carry a complete ecology they couldn’t carry enough food and oxygen in tanks. Because they will take generations to complete their journeys, they must also carry a viable and complete society.
     Clearly we’re talking about quite a large ship, with a population in the hundreds at least: high enough to prevent genetic drift. Centrifugal force substitutes for gravity. We’re going to be doing a lot of that. We spin the ship on its axis, and put all the things that need full gravity at the outside, along the hull. Plant rooms, exercise rooms, et cetera. Things that don’t need gravity, like fuel and guidance instruments, we line along the axis. If our motors thrust through the same axis, we will have to build a lot of the machinery on tracks, because the aft wall will be the floor when the ship is under power
     The “Universe” ship is basic to a discussion of life in space. We’ll be talking about much larger structures, but they are designed to do the same things on a larger scale: to provide a place to live, with as much security and variety and pleasure as Earth itself offers-or more.

     The fourth method is to accelerate all the, way, making turnover at the midpoint and decelerating the rest of the way. This works fine. Over interstellar distances it would take an infinite fuel supply—and by God we may have it, in the Bussard ramjet. A Bussard ramlet would use an electromagnetic field to scoop up the interstellar hydrogen ahead of it—with an intake a thousand miles or more in diameter—compress it, and burn it as fuel for a fusion drive. Now the multi-generation ship would become unnecessary as relativity shortens our trip time: four years to the nearest star, twenty.ŕne years to the galactic hub, twenty-eight to Andromeda galaxy—all at one gravity acceleration.
     The Bussard ramjet looks unlikely. It’s another ultimate, like generated gravity. Is the interstellar medium sufficiently ionized for such finicky control? Maybe not. But it’s worth a try.
     Meanwhile; our first step to other worlds is the “Universe” ship-huge, spun for gravity, its population in the hundreds, its travel time in generations.


     But we don’t really need spindizzies or generated gravity to build flying cities. In fact, we don’t really need to fill out Heinlein’s “Universe” ship. The outer hull is all we need. Visualize a ship like this:
  1. Cut a strip of Los Angeles, say, ten miles long by a mile wide.
  2. Roll it in a hoop. Buildings and streets face inward.
  3. Roof it over with glass or something stronger.
  4. Transport it to space. (Actually we’ll build it in space.)
  5. Reaction motors, air and water recycling systems, and storage areas are in the basement, outward from the street level. So are the fuel tanks. Jettisoning an empty fuel tank is easy. We just cut it loose, and it falls into the universe.
  6. We’re using a low-thrust, high-efficiency drive: ion jets, perhaps. The axis of the city can be kept clear. A smaller ship can rise to the-axis for sightings before a course change; or we can set the control bridge atop a slender fin. A ten mile circumference makes the fin a mile and a half tall if the bridge is at the axis; but the strain on the structure would diminish approaching the axis.
     What would it be like aboard the Ring City? One gravity everywhere, except in the bridge. We may want to enlarge the bridge to accommodate a schoolroom; teaching physics would be easier in free fall.
     Otherwise it would be a lot like the Generation ship. The populace would be less likely to forget their destiny, as Heinlein’s people did. They can see the sky from anywhere in the city; and the only fixed stars are Sol and the target star.
     It would be like living anywhere, except that great attention must be paid to environmental quality. This can be taken for granted throughout this article. The more thoroughly we control our environment, the more dangerous it is to forget it.



The next step up in size is the hollow planetoid. I got my designs from a book of scientific speculation, Islands in Space, by Dandrige M. Cole and Donald W. Cox.

STEP ONE: Construct a giant solar mirror. Formed under zero gravity conditions, it need be nothing more than an Echo balloon sprayed with something to harden it, then cut in half and silvered on the inside. It would be fragile as a butterfly, and huge.

STEP TWO: Pick a planetoid. Ideally, we need an elongated chunk of nickel-iron, perhaps one mile in diameter and two miles long. (it must be nickle-iron. If planetoid is stony, it will just fly into gravel when you start it spinning)

STEP THREE: Bore a hole down the long axis.

STEP FOUR: Charge the hole with tanks of water. Plug the openings, and weld the plugs, using the solar mirror.

STEP FIVE: Set the planetoid spinning slowly on its axis. As it spins, bathe the entire mass in the concentrated sunlight from the solar mirror. Gradually the flying iron mountain would be heated to melting all over its surface. Then the heat would creep inward, until the object is almost entirely molten.

STEP SIX: The axis would be the last part to reach melting point. At that point the water tanks explode. The pressure blows the planetoid up into an iron balloon some ten miles in diameter and twenty miles long, if everybody has done their jobs right.

     The hollow world is now ready for tenants. Except that certain things have to be moved in: air, water, soil, living things. It should be possible to set up a closed ecology. Cole and Cox suggested setting up the solar mirror at one end and using it to reflect sunlight back and forth along the long axis. We might prefer to use fusion power, if we’ve got it.
     Naturally we spin the thing for gravity.
     Living in such an inside-out world would be odd in some respects. The whole landscape is overhead. Our sky is farms and houses and so forth. If we came to space to see the stars, we’ll have to go down into the basement.
     We get our choice of gravity and weather. Weather is easy. We give the asteroid a slight equatorial bulge, to get a circular central lake. We shade the endpoints of the asteroid from the sun, so that it’s always raining there, and the water runs downhill to the central lake. If we keep the gravity low enough, we should be able to fly with an appropriate set of muscle-powered wings; and the closer we get to the axis, the easier it becomes. (Of course, if we get too close the wax melts and the wings come apart…)


     Let’s back up a bit, to the Heinlein “Universe” ship. Why do we want to land it?
     If the “Universe” ship has survived long enough to reach its target star, it could probably survive indefinitely; and so can the nth-generation society it now carries. Why should their descendants live out their lives on a primitive Earthlike world? Perhaps they were born to better things.
     Let the “Universe” ship become their universe, then. They can mine new materials from the asteroids of the new system, and use them to enlarge the ship when necessary, or build new ships. They can loosen the population control laws. Change stars when convenient. Colonize space itself, and let the planets become mere way-stations. See the universe!
     The concept is called Macrolife. Macrolife is large, powered, self-sufficient environments capable of expanding or reproducing. Put a drive on the inside-outside asteroid bubble and it becomes a Macro life vehicle. The ring-shaped flying city can be extended indefinitely from the forward rim. Blish’s spindizzy cities were a step away from being Macrolife; but they were too dependent on planet based society.
     A Macrolife vehicle would have to carry its own mining tools and chemical laboratories, and God knows what else. We’d learn what else accidentally, by losing interstellar colony ships. At best a Macrolife vehicle would never be as safe as a planet, unless it was as big as a planet, and perhaps not then. But there are other values than safety. An airplane isn’t as safe as a house, but a house doesn’t go anywhere. Neither does a world.


     Freeman Dyson’s original argument went as follows, approximately.
     No industrial society has ever reduced its need for power, except by collapsing. An intelligent optimist will expect his own society’s need for power to increase geometrically, and will make his plans accordingly. According to Dyson, it will not be an impossibly long time before our own civilization needs all the power generated by our sun. Every last erg of it. We will then have to enclose the sun so as to control all of its output.
     What we use to enclose the sun is problematic. Dyson was speaking of shells in the astronomical sense: solid or liquid, continuous or discontinuous, anything to interrupt the sum light so that it can be turned into power. One move might be to convert the mass of the solar system into as many little ten-by-twenty-mile hollow iron bubbles as will fit. The smaller we subdivide the mass of a planet, the more useful surface area we get. We put all the little asteroid bubbles in circular orbits at distances of about one Earth orbit from the sun, but differing enough that they won’t collide. It’s a gradual process. We start by converting the existing asteroids. When we run out, we convert Mars, Jupiter, Saturn, Uranus … and eventually, Earth.
     Now, aside from the fact that our need for power increases geometrically, our population also increases geometrically. If we didn’t need the power, we’d still need the room in those bubbles. Eventually we’ve blocked out all of the sunlight. From outside, from another star, such a system would be a great globe radiating enormous energy in the deep infrared.
     What some science fiction writers have been calling a Dyson sphere is something else: a hollow spherical shell, like a ping pong ball with a star in the middle. Mathematically at least, it is possible to build such a shell without leaving the solar system for materials. The planet Jupiter has a mass of 2 × 1030 grams, which is most of the mass of the solar system excluding the sun. Given massive transmutation of elements, we can convert Jupiter into a spherical shell 93 million miles in radius and maybe ten to twenty feet thick. If we don’t have transmutation, we can still do it, with a thinner shell. There are at least ten Earth masses of building material in the solar system, once we throw away the useless gasses.
     The surface area inside a Dyson sphere is about a billion times that of the Earth. Very few galactic civilizations in science fiction have included as many as a billion worlds. Here you’d have that much territory within walking distance, assuming you were immortal.
     Naturally we would have to set up a biosphere on the inner surface. We’d also need gravity generators. The gravitational attraction inside a uniform spherical shell is zero. The net pull would come from the sun, and everything would gradually drift upward into it.
     So. We spot gravity generators all over the shell, to hold down the air and the people and the buildings. “Down” is outward, toward the stars.
     We can control the temperature of any locality by varying the heat-retaining properties of the shell. In fact, we may want to enlarge the shell, to give us more room or to make the permanent noonday sun look smaller. All we need do is make the shell a better insulator: foam the material, for instance. If it holds heat too well, we may want to add radiator fins to the outside.
     Note that life is not necessarily pleasant in a Dyson sphere. We can’t see the stars. It is always noon. We can’t dig mines or basements. And if one of the gravity generators ever went out, the resulting disaster would make the end of the Earth look trivial by comparison.
     But if we need a Dyson sphere, and if it can be built, we’ll probably build it.
     Now, Dyson’s assumptions (expanding population, expanding need for power) may hold for any industrial society, human or not. If an astronomer were looking for inhabited stellar systems, he would be missing the point if he watched only the visible stars. The galaxy’s most advanced civilizations may be spherical shells about the size of the Earth’s orbit, radiating as much power as a Sol-type sun, but at about 1O angstroms wavelength—in the deep infrared…
     …assuming that the galaxy’s most advanced civilizations are protoplasmic. But beings whose chemistry is based on molten copper, say, would want a hotter environment. They might have evolved faster, in temperatures where chemistry and biochemistry would move far faster. There might be a lot more of them than of us. And their red-hot Dyson spheres would look deceptively like red giant or supergiant stars. One wonders.
     In The Wanderer, novelist Fritz Leiber suggested that most of the visible stars have already been surrounded by shells of worlds. We are watching old light, he suggested, light that was on its way to Earth before the industrial expansion of galactic civilization really hit its stride. Already we see some of the result: the opaque dust clouds astronomers find in the direction of the galactic core are not dust clouds, but walls of Dyson spheres blocking the stars within.


     I myself have dreamed up an intermediate step between Dyson spheres and planets. Build a ring 93 million miles in radius—one Earth orbit—which would make it 600 million miles long. If we have the mass of Jupiter to work with, and if we make it a million miles wide, we get a thickness of about a thousand meters. The Ringworld would thus be much sturdier than a Dyson sphere.
     There are other advantages. We can spin it for gravity. A rotation on Its axis of 770 miles/second would give the Ringworld one gravity outward. We wouldn’t even have to roof itover. Put walls a thousand miles high at each rim, aimed inward at the sun, and very little of the air will leak over the edges.
     Set up an inner ring of shadow squares—light orbiting structures to block out part of the sunlight—and we can have day-and-night cycles in whatever period we like. And we can see the stars, unlike the inhabitants of a Dyson sphere.
     The thing is roomy enough; three million times the area of the Earth. It will be some time before anyone complains of the crowding.
     As with most of these structures, our landscape is optional, a challenge to engineer and artist alike. A look at the outer surface of a Ringworld or Dyson sphere would be most instructive. Seas would show as bulges, mountains as dents. River beds and river deltas would be sculpted in; there would be no room for erosion on something as thin as a Ringworld or a Dyson sphere. Seas would be flat-bottomed—as we use only the top of a sea anyway—and small, with convoluted shorelines. Lots of beachfront. Mountains would exist only for scenery and recreation.
     A large meteor would be a disaster on such a structure. A hole in the floor of the Ringworld, if not plugged, would eventually let all the air out, and the pressure differential would cause storms the size of a world, making repairs difficult.

     The Ringworld concept is flexible. Consider:
  1. More than one Ringworld can circle a sun. Imagine many Ringworlds, noncoplanar, of slightly differing radii—or of widely differing radii, inhabited by very different intelligent races.
  2. We’d get seasons by bobbing the sun up and down. Actually the Ring would do the bobbing; the sun would stay put. (One Ring to a sun for this trick.)
  3. To build a Ringworld when all the planets in the system are colonized to the hilt (and, baby, we don’t need a Ringworld until it’s gotten that bad!) pro tem structures are needed. A structure the size of a world and the shape of a pie plate, with a huge rocket thruster underneath and a biosphere in the dish, might serve to house a planet’s population while the planet in question is being disassemb1ed. It circles the sun at 770 miles/second, firing outward to maintain its orbit. The depopulated planet becomes two more pie plates, and we wire them in an equilateral triangle and turn off the thrusters, evacuate more planets and start building the Ringworld.


     I pointed out earlier that gravity generators look unlikely. We may never be able to build them at all. Do we really need to assume gravity generators on a Dyson sphere? There are at least two other solutions.
     We can spin the Dyson sphere. It still picks up all the energy of the sun as planned; but the atmosphere collects around the equator, and the rest is in vacuum. We would do better to reshape the structure like a canister of movie film; it gives us greater structural strength. And we wind up with a closed Ringworld.
     Or, we can live with the fact that we can’t have gravity. According to the suggestion of Dan Aiderson, Ph.D., we can built two concentric spherical shells, the inner shell transparent, the outer transparent or opaque, at our whim. The biosphere is between the two shells.
     It would be fun. We can build anything we like within the free fall environment. Buildings would be fragile as a butterfly. Left to themselves they would drift up against the inner shell, but a heavy thread would be enough to tether them against the sun’s puny gravity. The only question is, can humanity stand long periods of free fall?


     What’s bigger than a Dyson sphere? Dan Alderson, designer of the Alderson Double Dyson Sphere, now brings you the Alderson Disc. The shape is that of a phonograph record, with a sun situated in the little hole. The radius is about that of the orbit of Mars or Jupiter. Thickness: a few thousand miles.
     Gravity is uniformly vertical to the surface (freshman physics again) except for edge effects.. Engineers do have to worry about edge effects; so we’ll build a thousand-mile wall around the inner well to keep the atmosphere from drifting into the sun. The outer edge will take care of itself.
     This thing is massive. It weighs far more than the sun. We ignore problems of structural strength. Please note that we can inhabit both sides of the structure.
     The sun will always be on the horizon, unless we bob it, which we do. (This time it is the sun that does the bobbing.) Now it is always dawn, or dusk, or night.
     The Disc would be a wonderful place to stage a Gothic or a swords-and-sorcery novel. The atmosphere is right, and there are real monsters. Consider: we can occupy only a part of the Disc the right distance from the sun. We might as well share the Disc and the cost of its construction with aliens from hotter or colder climes. Mercurians and Venusians nearer the sun, Martians out toward the rim, aliens from other stars living wherever it suits them best. Over the tens of thousands of years, mutations and adaptations would migrate across the sparsely settled borders. If civilization should fall, things could get eerie and interesting.


     Pat Gunkel has designed a structure analogous to the Ringworld. Imagine a hollow strand of macaroni six hundred million miles long and not particularly thick-say a mile in diameter. Join it in a loop around the sun.
     Pat calls it a topopolis. He points out that we could rotate the thing as in the illustration—getting gravity through centrifugal force—because of the lack of torsion effects. At six hundred million miles long and a mile wide, the curvature of the tube is negligible. We can set up a biosphere on the inner surface, with a sunlight tube down the axis and photoelectric power sources on the outside. So far, we’ve got something bigger than a world but smaller than a Ringworld.
     But we don’t have to be satisfied with one loop! We can go round and round the sun, as often as we like, as long as the strands don’t touch. Pat visualizes endless loops of rotating tube, shaped like a hell of a lot of spaghetti patted roughly into a hollow sphere with a star at the center (and now we call it an aegagropilous topopolis.) As the madhouse civilization that built it continued to expand, the coil would reach to other stars. With the interstellar links using power supplied by the inner coils, the tube city would expand through the galaxy. Eventually our aegagropilous galactotopopolis would look like all the stars in the heavens had been embedded in hair.


     Mathematically at least, it is possible to build a really big Dyson sphere, with the. heart of a galaxy at its center. There probably aren’t enough planets to supply us with material. We would have to disassemble some of the star of the galactic arms. But we’ll be able to do it by the time we need to.
     We put the biosphere—on the outside this time. Surface. gravity is minute, but the atmospheric gradient is infinitesimal. Once again, we assume that it is possible for human beings to adapt to free fall. We live in free fall, above a surface area of tens of millions of light years, within an atmosphere that doesn’t thin out for scores of light years.
     Temperature control is easy: we vary the heat conductivity of the sphere to pick up and hold enough of the energy from the stars within. Though the radiating surface is great, the volume to hold heat is much greater. Immustrial power would come from photoreceptors inside the shell.
     Within this limitless universe of air we can build exceptionally large structures, Ringworld-sized and larger. We could even spin them for gravity. They would remain aloft for many times the lifespan of any known civilization before the gravity of the Core stars pulled them down to contact the surface.
     The Megasphere would be a pleasantly poetic place to live. From a flat Earth hanging in space, one could actually reach a nearby moon via a chariot drawn by swans, and stand a good chance of finding selenites there. There would be none of this nonsense about carrying bottles of air along.


     One final step to join two opposing life styles, the Macrolife tourist types and the sedentary types who prefer to restructure their home worlds.
     The Ringworld rotates at 770 miles/second. Given appropriate conducting surfaces, this rotation could set up enormous magnetic effects. These could be used to control the burning of the sun, to cause it to fire off a jet of gas along the Ringworld axis of rotation. The sun becomes its own rocket. The Ringworld follows, tethered by gravity.
     By the time we run Out of sun, the Ring is moving through space at Bussard ramjet velocities. We continue to use the magnetic effect to pinch the interstellar gas into a fusion flame, which now becomes our sun and our motive power.
     The Ringworld makes a problematical, vehicle. What’s it for? You can’t land the damn thing anywhere. A traveling Ringworld. is not useful as a tourist vehicle, anything you want to see, you can put on the Ringworld itself… unless it’s a lovely multiple star system like Beta Lyrae but you just can’t get that close on a flying Ringworld.
     A Ringworld in flight would be a bird of ill omen. It could only be fleeing some galaxy-wide disaster.
     Now, galaxies do explode. We have pictures of it happening. The probable explanation is a chain reaction of novae in the galactic core. Perhaps we should be maintaining a space watch for fleeing Ringworlds… except that we couldn’t do anything about it.

From BIGGER THAN WORLDS by Larry Niven (1974)

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