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Planet Spaceship

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Seldom has 'starship' been so literal... or insufficient.

"...Brave as fools and bold as gods, they built an armada of swift little ships and raced out to meet me, and to my utter amazement, I discovered that I was enormous- bigger than worlds, massive and enduring, and in their spellbound eyes, beautiful."
— The Great Ship

There's big spaceships, there's gigantic spaceships, and then there's these: a space ship (or station) that's as big as a small planet or large moon. In space, you have no external gravity to contend with, so it's possible to build some truly humongous structures like this. Alternatively, you may just want to strap some engines onto an actual planet or moon and set off, although this may require Sufficiently Advanced Technology. If the ship's big enough, it may even have its natural gravity be big enough to keep things rooted to its surface, though usually not enough to make an earth-like atmosphere (like, say, our moon).

Often used for Rule of Cool, in which case it will overlap with Cool Starship, the Planet Spaceship is a great way to intimidate your foe, or to pack your entire population off when your home world is in trouble. May evoke a "That's No Moon!" reaction when it first appears.


Technically, actual planets and moons are spacecraft in the sense that they are in orbit around something. Buckminster Fuller made this analogy when he referred to "Space Ship Earth." But to qualify for this trope, the super-colossal spacecraft must have some means of propulsion, or at the very least orbital correction.

Subtrope of Mile-Long Ship. May be used as a Big Dumb Object, The Battlestar, or a Generation Ship. Commonly, though not exclusively, found in Space Opera. Compare Dyson Sphere and Ring World Planet. See also: Unnecessarily Large Vessel, Unnecessarily Large Interior and Awesome, but Impractical.



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    Anime & Manga 
  • The Zentradi main base in Super Dimension Fortress Macross is hundreds of kilometers across. Of course, the Zentradi themselves are giants.
  • There's a ship in the Raalgon fleet, in Irresponsible Captain Tylor, that causes Tylor himself to comment that it's "more like a planet than a ship".
    • And it is outclassed by an even bigger ship in the final OVA.
  • In Tengen Toppa Gurren Lagann, the final battle has the two sides fighting with mechas that are on the same scale as galaxies!
    • You don't even need to go that far to find planetoid-sized vessels in TTGL. The Super Galaxy Gurren Lagann/Cathedral Terra was large enough to be disguised as the moon.
  • Transformers Cybertron: The planet Cybertron, the alternate mode of Primus (basically the transformers god), can transform into a spaceship of sorts.
  • In Outlanders, Earth's moon is revealed to be a millennia-old ship, the superweapon called "Dola".
  • Lord Slugg's planet-ship in Dragon Ball Z. It's actually a regular ship attached to whatever planet it conquered and terra-froze.
  • In the five-part series finale of Kirby: Right Back at Ya!, Nightmare Enterprises is revealed to be housed by a massive space station that's about the size of a small planet.

    Comic Books 
  • Taa II, the Worldship belonging to the Marvel Comics character Galactus, and named after his ravaged homeland Taa, is the size of a solar system.
  • Disney Ducks Comic Universe stories from Italy have more than a few:
    • The first to appear is Pacificus, Reginella's homeworld. It doesn't have full control over its course, but can change speed and manouver on a number of pre-decided routes.
    • The second is Vampirione. It has better manouvering abilities than Pacificus but is slower, as shown when its inhabitants chase Pacificus to try and steal all its resources.
    • The Evronians from Paperinik New Adventures love this trope:
      • At some point in the past they took their homeworld and turned it into a spaceship. Never appeared on page and is only mentioned in the inserts, but may have been destroyed off-screen by Xadhoom (the flashback showing her destroying one such place shows one that doesn't exactly look like the one we saw her destroy on-page).
      • Zotnam's mothership is relatively small, only 500 km long and tall. Fate of this one unknown.
      • The "Xadhoom's Trilogy" provides a third, described the size of a small planet. It's ultimately wrecked by Xadhoom and a Coolflame revolt and explodes.
      • The first relaunch story, "Might and Power", shows that the Evronians in the Bad Future did it again: they transformed another planet in a spaceship, in this case Earth. It took them two hundred years.
      • A fifth shows up in "Chronicle of a Return", surprising Paperinik because he thought they only had one. Much to his horror, the Evronians there explain him that they do it regularly: whenever the population of one grows too much they build one or turn a planet into one, divide their population in two, and then the two spaceship go their separate ways, ready to repeat the process when the population grows too much again. Also effectively confirming that Xadhoom had destroyed two Evronian planet spaceships... But maybe not the original.
  • Mogo, the Sentient Planet is a Green Lantern, and effectively becomes this as he can travel through hyperspace.
    • Mogo also has a rival in Ranx the Sentient City, who was once prophesied to destroy Mogo and was rather eager to fulfill this prophecy.
  • Warworld, which frequently falls into the hands of Superman's Galactic Conqueror enemies.
  • In DC`s New 52 Green Lantern: New Guardians series there was a whole artificial solar system, with inhabitable interiors for various species, it was built to replace the star system Larfleeze the orange lantern inhabits.
  • 2000 AD:
    • The Ten-Seconders: Sort of. The "Fathers" of the superhero-esque Gods live in a spaceship big enough to easily engulf Planet Earth.
    • Shakara:
      • The Succubi hive species travel around in cosmos crafts that are about the size of a small planet.
      • Shakara himself uses a World Engine to transform an entire planet into a giant rocket, using it to blast through an alien fleet.
  • The Empyreon in Khaal: The Chronicles of a Galactic Emperor is an ancient prison ship so massive its capable of supporting its own (dwindling) ecosystem and homes three separate civilizations that are fighting among themselves for its scarce resources.
  • Star Trek: Mission's End takes place on Archenar-IV. Originally it was merely a giant spaceship, but it's original crew disappeared. In the thousands of years since it insect population has evolved sentience and treat the place like their home planet.

    Fan Works 

    Film - Animated 
  • Titan, for which Titan A.E. is named, is a very large, spherical spaceship. When activated, it converts energy into mass and turns into an actual planet.
  • In an early draft and Marvel's Comic-Book Adaptation of The Transformers: The Movie, Junkeon is revealed to be one with the Autobots flying it to Cybertron rather than finding a ship.

    Film - Live Action 
  • Star Wars
    • The Death Star in the first and third films is a moon-sized superweapon which is the original source of the That's No Moon! trope. For specificity's sake, the first Death Star was established as 160 kilometers in diameter, and the second would've been 900 kilometers or twice as big as the first one (there are contradictory reports) if it hadn't been blown up first.
    • In The Force Awakens, Starkiller Base is the Death Star Up to Eleven. It's an alpine planet that's been converted into a superweapon, making it many times larger than the Death Star. However, it doesn't move, at least on screen; since it eats stars to fuel its super-cannon, it was presumably intended to relocate once the system it was in ran out of stars to eat.
  • Spaceball One in the movie Spaceballs, a parody of Star Wars, has a similar scale.
  • The alien mothership in Independence Day was estimated to be several hundred kilometers in diameter. Independence Day: Resurgence tops it with a larger mothership that dwarfs the Atlantic ocean and has its own ecosystem.
  • The Tet from Oblivion.
  • In Little Shop of Horrors, Audrey II beams down to Earth during an unprecedented eclipse, implying that he came here in a spaceship large enough to block out the sun.
  • Star Trek Beyond has Starbase Yorktown, a moon-sized space station that contains interlocking rings for habitation, the equivalent of several planetbound cities holding millions of people.
  • Alpha from Valerian and the City of a Thousand Planets. It started as our world's ISS, then other nations of the world expanded it with their own vessels, then alien vessels from all over the universe expanded it further. It size and mass started causing a serious problem to Earth and thus Alpha was freed from its orbit.

  • In the Ted Reynolds short story, "Ker-Plop", we get a reminder of the difference between size and volume, when humans return from the Magellanic Clouds in a ship that is ten thousand kilometers across (for comparison, Earth is a little over 12,000km across). The agent sent to investigate realizes that because the entire volume is inhabited, rather than just the surface, this one ship contains more people than his entire galactic federation. The decks are arranged concentrically, like an onion, and the first kilometer alone has nearly 400 decks, each with nearly the same surface area as the entire ship!
  • In E. E. “Doc” Smith's Skylark Series, Drs. Seaton and Crane build a 1000km diameter spaceship called the Skylark of Valeron. Its size was needed to house the sensors required to travel at its full velocity. Later, their rival Dr. DuQuesne builds an even bigger ship.
  • In Larry Niven's Known Space series, the Pierson's Puppeteers are a race of cowards, and the only Puppeteers humans have met are insane— because no sane Puppeteer would trust his life to something so fragile as a spaceship. So when they discover a massive wave of radiation approaching their home system, they leave it behind... but take their planets with them. They put them in orbit around each other (see Klemperer Rosette on The Other Wiki) and accelerated them to just under lightspeed, heading out of the galaxy. Because humans have faster than light starships (which Puppeteers are too sane to use), they expect humans to greet them at their destination, the Clouds of Magellan.
  • In the Gor series:
    • The planet Gor itself can be considered an example, since the Priest-Kings (the Physical Gods of the planet) moved it to its current location 5 million years ago.
    • The Kurii live in "Steel Worlds" in the asteroid belt; from there they plot their plans to destroy the Priest-Kings and take over Gor & Earth for themselves. The Steel Worlds have aritifical weather & daytime/nighttime and rotate to simulate gravity, with beings living on the inside circumferance of the ships. They used to have a planet of their own but they destroyed it making war with each other.
  • David Weber's Empire from the Ashes series has Dahak and all the other Imperial Planetoids. Dahak has spent the last 50,000 years pretending to be Earth's Moon... and it's the smallest of them. They come equipped with hundred kilometer thick armor and carry 80,000 ton battleships as parasite craft.
  • In John Varley's Gaea Trilogy, Gaea and her brood are living space habitats large enough to be mistaken for additional moons of Saturn.
    • Varley also uses this trope in his short story "The Funhouse Effect": a large comet in a close solar orbit is partially hollowed out, has engines mounted on it and is being used for exclusive pleasure cruises 'round the Sun.
  • In The City and the Stars by Arthur C. Clarke, it is revealed at the end that most of the humanity left the Galaxy to explore the universe... in a star cluster made into a fleet.
  • At the end of Halo: The Cole Protocol, the Rubble's inhabitants, who are survivors of the previous Covenant invasion of their system, convert a large asteroid into an evacuation ship to get everyone safely to UNSC space.
  • In Remnants, eighty humans blast off in a slapped-together rocket with experimental stasis technology in hopes of surviving when an asteroid hits Earth. Those who wake up initially think that they've landed on a bizarre alien world. They soon discover that it's actually a massive spaceship with artificial environments; its sentient (and unfortunately crazy) AI, Mother, brought them aboard as a curiosity. The dimensions of the ship are later given as about 100 x 150 miles.
  • The My Teacher Is an Alien series has a ship called the New Jersey, so called because it's the size of New Jersey. (It's actually an alien spaceship, but christened by a fan of Earth.) Its inhabitants use Teleporters and Transporters to get around rather than walk hundreds of miles from one place to another.
  • In Robert Reed's Great Ship series, the Great Ship itself is an ancient abandoned artifact which was claimed and settled by mankind's descendents. It is larger than Jupiter. The interior of the ship has hundreds of thousands of enormous caverns which are inhabited by the passengers. The ship has fourteen gimbaled engines on one end, which are fed from dozens of hydrogen fuel tanks whose individual volume exceeds that of all the Earth's oceans combined by several orders of magnitude. In The Well of Stars, a planet weapon is shown - the Sword of Creation - a planet-wide hyperfiber ring which has microscopic black holes tethered to its rim, which is then spun up and repeatedly launched at planets to expose a path to its core for mining.
  • Cordwainer Smith gives us The Golden Ship - a sphere 90 million miles in length (just 2 million miles short of an AU). That's approximately 100 times larger than Earth's sun! Extremely fast, it could move in seconds. However, the Golden Ship is really a decoy, being mostly hollow and consisting of foam and wires. It has no weapons of its own, and must rely on its speed to survive.
  • The largest vessels in the Perry Rhodan series fall under this trope. For instance the cosmocratic spore ships, spheres with a size of 1126 kilometers.
    • Possibly the most extreme examples: Klongheim and Parsfon, the fully FTL-capable homes of rival robot civilizations traveling the universe in search of their rightful masters, with dimensions measured in light-months. It's strongly suggested that these got their start as remnants of some cosmic disaster or other that weren't so much built as colonized.
  • Terre En Fuite (Fleeing Earth) is a novel by François Bordes where Earth (with the Moon in natural gravitational tow) and Venus are turned into giant spaceships in order to allow humanity to escape the Sun going nova. Initially, the plan is to wait out the explosion behind Jupiter and come back. However, scientist then determine that the Sun will not return to its former state, so they have to move the planets to another system... and then again when the first one turns out to have a Lost Colony of humans.
  • In The Witches of Karres, the so-called witches use their "Sheewash drive" to move the entire planet of Karres around when they need to.
  • In the Star Wars Expanded Universe:
    • Zonama Sekot is a case of attaching absolutely enormous hyperdrive engines to a (sapient) Earthlike planet.
    • The Yuuzhan Vong have massive Worldships which hold most of the races population. They were used by the Vong to travel from their galaxy to the galaxy of the protagonists. They're also used as warships, and are thrice the size of a Super Star Destroyer.
    • The Crystal Star has Worldships, artificial planetoids with hyperdrive engines. They're large enough that people on the surface can mistake them for planets and even have their own synthetic "suns", but are small enough to rely on artificial gravity.
  • In the Piers Anthony book Macroscope, Sufficiently Advanced Technology allows four humans to turn the entire planet Neptune into a machine that can carry them to different locations in space instantly, tesseract-style.
  • The larger models of Culture General Systems Vehicle from Iain Banks' The Culture fall here. The things can be anywhere from 25 to 200 kilometers in size, and carry millions of passengers and can match planets for industrial production. One scene shows four kilometer oceangoing ships being packed away for storage inside a GSV.
  • In the Star Carrier novels the Turusch build their larger warships by hollowing out large asteroids and adding engines. An extreme example of this is the Regrets of Parting, made from a dwarf planet at least 900 kilometers in diameter and massing about 900 quadrillion tonnes.
  • Edmond Hamilton gives us "Thundering Worlds," in which every planet in the solar system is outfitted with nuclear rockets and flown to another solar system to escape our dying sun. Of course, then they pass by some hostile aliens and give them the same idea...
  • The Polish sci-fi novel for teenagers Ci z dziesiątego tysiąca (Ones from the Tenth Thousand) by Jerzy Broszkiewicz mostly takes place on a "mechanoplanet": a large, intelligent spherical spaceship with artificial environment.
  • In the final book of the Tunnels series, Planet Earth itself is revealed to be one of these.
  • When the aliens of Greg Egan's Orthogonal trilogy develop their Perpetual Motion Machine engines that are powered by light and consume (almost) no fuel, some characters discuss building massive engines on the Doomed Home Planet and "flying" the planet to safety like a straightforward Planet Spaceship. At/after the end of the trilogy, though, they instead put out the sun and build engines on its surface, so that they can move it and let its gravity take care of pulling the planet along, which will cause fewer siesmic disturbances on the planet. This is at least partially justified in that, In-Universe, the sun actually is just a big ball of flammable rock that is on fire, not a ball of gas undergoing a continuous fusion reaction.
  • In the Paradox Trilogy, the xith'cal have no colony worlds. They live on tribe ships, moon-sized spaceships which hold millions or even tens of millions of xith'cal.
  • The short story "With Friends Like These" by Alan Dean Foster has a literal Spaceship Earth, at the end. Aliens come to recruit humanity, who have been trapped on earth after being kicked out of Galactic society for fighting. After they agree, the entire planet follows them, bringing the moon along with it.
  • In the Xeelee Sequence, humanity uses celestial objects in their misguided war against the lords of the baryonic universe, the Xeelee and their Great Attractor. In Flux, humanity converted a neutron star into a starship, sinking a Reactionless Drive beneath the crust, uploading minds into computronium in the core, and building nigh-microscopic human analogues to tend machinery on the crust. In the finale to the Vacuum Diagrams short story collection, the Qax lead an assault on the photino birds around the Attractor, using a red giant star as a flagship.

    Live-Action TV 
  • In Andromeda the Magog come from worlds (yes, that's plural—twenty of them) locked together in some kind of structure. The whole thing is mobile, FTL capable, and even contains an artificial sun. Oh, and it can survive a hit from a Nova Bomb, the largest weapon in the Commonwealth arsenal, normally capable of nuking entire solar systems.
  • In the Star Trek: The Original Series ep. "For the World is Hollow and I Have Touched the Sky" a group of aliens have been sequestered inside a large interstellar asteroid for so long that they have forgotten that they are actually inside one.
  • Doctor Who has had one or two in its 50-year history.
    • First, the Daleks attempted it in "The Dalek Invasion of Earth," but failed. The second, and somewhat more successful of these, was Zanak from "The Pirate Planet," a hollowed-out planet with massive transmat engines... it could materialize around another planet and capture everything from it, leaving behind a tiny husk, which its captain could collect as a trophy.
    • The TARDIS itself definitely qualifies, just not on the outside. Its exact inner size is variable, but we know that it's large enough to contain an Eye of Harmony, a Time Lord power source built from a nearly-dead star in a perpetual state of gravitational collapse. The Doctor once claimed that if the TARDIS ever tried to land without its shell, the ship's true weight would crack the surface of the Earth. And even before that, he'd previously said that the TARDIS is, for all intents and purposes, infinite.
  • One of the First Ones featured on Babylon 5 operated a planet whose power source was the core of a planet, retrofitted for space travel. It even appeared to have a ring of moons.

  • The closest Real Life equivalent to the fictionals examples for this trope are Rogue planets, that roam free across interstellar space, be them bodies that formed the same way stars do or planets ejected from a star system. Since we can detect just the largest and youngest ones it's perfectly conceivable that there'd be a lot of them out there, down to Earth-sized ones or less.

  • In The BBC's 1980s series Earthsearch the descendants of a starship's original crew arrive back at Earth's solar system 150 years after the ship set out, only to find it gone. The title refers to their attempt to find out where it was taken. They've actually been gone for millions of years due to Time Dilation. Oh, and it's not the planet we call Earth.

    Tabletop Games 
  • In Warhammer 40,000:
    • Eldar craftworlds are described as "planetoid-sized".
    • The Necron World Engine, unsurprisingly, is a Necron ship the size of a planet (because they slapped an engine on a planet). An entire space marine chapter sacrificed itself to give an enormous Imperial fleet a fighting chance.
    • Also, the Phalanx is the moon-sized fortress-monastery-spaceship of the Imperial Fists.
    • On a smaller scale, ork roks are asteroids and other large celestial bodies that have been hollowed out, filled with orks, sealed against vacuum, and fitted with ginormous engines to be sent through the Warp. Once close to a planet, they then serve as one-time Drop Pods.
  • World Of Synnabar takes place in a spaceship made from a hollowed out Mars.
  • In Pathfinder, Apostae, the tenth planet from Golarion's sun, called "The Messenger", is one of these. It's a Generation Ship, with it's crew/cargo trapped inside, horribly mutated and deformed, having long since lost control of the ship and memory of their mission, if they ever had it to begin with.

  • In BIONICLE, Mata Nui was designed to observe other universes while having beings inside him functioning as Nano Machines in a sense. His Humongous Mecha body is roughly forty million feet (7,575 mi or 12,192 km) tall and had a camouflage system that created an island on his face. Mata Nui was able to control specific things like gravity and light within his body.

    Video Games 
  • In Marathon, the eponymous ship was originally Mars' moon Deimos. This is less impressive than it sounds given that Deimos is about six kilometers long... fairly big by human standards, but nowhere near the size of a planet.
  • The Dammerung in Xenosaga is described in the accompanying Perfect Works manual as an artificial planet the size of Lebanon. It's the headquarters for Fiction 500 company Vector, and contains at least one megalopolis in an area large enough to have a real weather system.
  • In the videogame adaptation of Futurama, Mom's plot involves transforming the Earth into a giant spaceship.
  • In Star Ruler, the players can make ships anywhere from the size of a coke can to ships larger than the galaxy. At around ship scale 1000, ships start to become larger than the planets that build them. Additionally, it's possible to turn entire planets into ships by researching the Planetary Thruster. Building a bunch of planetary thrusters, some shield generators, and planetary laser cannons essentially turns the planet into a ridiculously durable, but relatively poorly armed ship with the capacity to store thousands of smaller ships, or build more ships on the way to its destination by importing goods from the galactic bank.
  • Sonic the Hedgehog has The Death Egg, a parody of the Death Star. The intro of Sonic & Knuckles illustrates just how big it is—the Eggman face fills the top of a volcano (Lava Reef, to be exact).
  • The X-Universe series' backstory provides an extreme example. Billions of years ago the Ancients fought a several-million-year-long war against a Kardashev Type V+ race called the Outsiders who are believed to have invaded from another universe. They entered ours in the form of several ships that were each the size of a solar system. (Yeah, Sufficiently Advanced Alien doesn't even begin to cover this.)
  • The first two games in the Might and Magic series has an implicit case: the worlds they take place on are indicated to be just two out of several carried by an Ancient automated vessel. Both CRON and VARN (the worlds in question) are decently-sized themselves, giving some inkling of the minimal size of the vessel. The third game does not actually take place on this ship, but the islands on planet it does take place on were once smaller such worlds on the ship that were placed on the planet by the Ancients as colonies. On a more minimal scale, the villain of World of Xeen (the combined IV/V) planned to use XEEN as this (the problem is that while it would indeed be entirely possible to do this, it'd kill the natives, at least with the villain's implementation).
  • The Voth fortress-ship in the Star Trek Online PVE raid "The Breach". Starfleet's Odyssey-class has been scaled as roughly a kilometer in length, and this thing probably dwarfs a hundred Oddys nose-to-stern. Oh, and it carries multiple Citadel-class dreadnoughts within it like fighters, each of them roughly 10 km long. Indeed, the official chart released by the devs when "The Breach" was launch lists it as 134.5 kilometers long. Meaning it can cover the entire San Francisco Bay Area.
  • In Meteos, the inhabitants of Darthvega destroyed their homeworld through war and now live in what looks like an octahedral Death Star.
  • X Com Enemy Unknown has the alien Temple Ship, which is roughly a size of Greenland. Bonus points for its gravitational pull causing earthquakes when it arrives.
  • Destiny fulfills this trope with Oryx's Dreadnaught: essentially a small pocket universe everted into realspace, filling the interior of a spaceship that some rough math places at around 3,500 kilometers long. The Hive put all that extra space to good use. The lore also makes reference to Hive "war-moons": whole moons hollowed out and turned into warships, and implies they're busy doing this to our moon.
  • The Jennerit from Battleborn have a massive moon-sized starship called the Exodus which houses the Sustainment Engine and massive power facilities capable of storing energy from other planets like Tempest the Jennerit throneworld for use in Sustainment. Despite its massive size, Exodus is capable of faster-than-light travel and often moves from planet-to-planet to collect vast amounts of energy to power Sustainment procedures. Many of the Sustained and those worthy of being Sustained live aboard Exodus, though some still reside on Tempest.
  • The Access Ark in Kirby: Planet Robobot looks to be nearly as big as Popstar itself in the opening cinematic and on the world map. It's the mothership of the Haltmann Works Company and is used to mechanize and invade planets before stripping them of their resources, though its true nature ends up being quite a surprise.
  • The Grineer Queens' Kuva Fortress in Warframe is a massive asteroid with spaceship engines built into it, allowing the Grineer high command to evade detection and attack from their enemies by constantly relocating their base of operations.

    Web Original 
  • The Ship Moves (Or Warhammer 50,000: Age of Exodus), a variation setting based off of Warhammer 40,000 crafted on the /tg/ board of 4chan.
    • It begins with the God-Emperor waking up and giving a set of orders before going back to bed. Said orders result in the creation of The Ship. With a keel of approximately One Astronomical Unit in length (1 AU = 149597871 kilometres, by definition the distance from the earth to the sun), the remains of the Imperium stripped to build it, Holy Terra itself hollowed out and fitted with cogitators and command system and the Imperial Palace itself becoming the bridge and God-Captain of Humanity guiding it.
    The Ship is the Imperium.
    The Imperium is the Ship.
    The Ship is the Emperor.
    The Emperor is the Ship.
    All is the Ship.
    The Ship is All.
    The Ship Moves.
  • In Schlock Mercenary a race of short-sighted robots packed their creators onto a Colony Ship made from a gas giant. It crashed.
  • Quentyn Quinn, Space Ranger:
    • One arc takes place on the Sapphire Star, a worldship of the Empire of the Seven Systems with a diameter in the tens of kilometers. It's used as a mid-range luxury cruise liner.
    • The 40K bash arc has the "Hyooman Empiyah" come into the galaxy in a fleet of shipworlds.
  • Orion's Arm: Taken Up to Eleven with the Leviathan, a galaxy spaceship. That is to say, it's the approximate mass of an entire galaxy moving under its own power, with an approximate size of 10 light-years. It is believed to consist of a huge number of Dyson Spheres connected in a giant net-like configuration. How in the hell someone managed to build something like this, or more importantly, why someone built something like this, is entirely unknown. Fortunately, since FTL travel is not possible in this 'verse, it'll be around 4 million years before anyone in the Milky Way has to worry about this thing...
  • The climax of A Miracle of Science features Mars' moon Deimos being used in this fashion, in this case to provide a credible threat to back up the main characters and get the Big Bad to stand down. It's also a clever use of Exact Words, as Mars is under treaty to never extend military force beyond the orbit of Deimos. If Deimos can move...

    Western Animation 
  • In Invader Zim, the original inhabitants of Mars drove themselves to extinction converting their planet into a giant spaceship... "Because it's cool". A similar thing happened to Mercury, which leads to an awesome dogfight.
  • Shadow Raiders feature a handful of planets with engines designed by an unknown precursor race. In fact the toyline it's loosely based on was called "War Planets".
  • Mission Control in Captain Star is described as "the largest object in Creation" and resembles a planet when briefly shown.