But sometimes they specialize in a particular area, like a farming planet providing produce to neighboring industrialized worlds that do not have enough arable land for food but have plenty of interstellar trade to buy. They are still diversified, but one purpose is emphasized.
And in science fiction, there are some colonies who turn it up to 11 and can only do one function. The classic example is a planetary Penal colony.
Remember in The Stars, Like Dust colonized planets go through a economic cycle of general roles:
- Step 1 - Subsistence Agricultural/Herding: newly colonized worlds focus on subsistence farming, all their energies expended in trying to feed itself.
- Step 2 - Developing: the world starts exporting. It mines crude ore and exports it along with agricultural surplus. In exchange it imports luxuries and machinery.
- Step 3 - Industrializing: the world starts building an industrial infrastructure as population grows and foreign investments increase. Local agriculture shrinks as food imports grow.
- Step 4 - Mechanized: The world is fully industrializd. It exports machinery, invests in other industrializing worlds, and imports most of its food.
Just try to avoid the Planet of Hats syndrome and one-product planets. Remember that each planet is a world, as big and diverse and old and mysterious as ever Terra was.
Obviously the simplist way to avoid the trope is to use two or more of these types on a given planet.
An initial settlement will be a "subsistence world", where the impoverished settlers work hard to keep themselves fed.
Once they have advanced to having surplus crops, they can think about selling it to off-planet customers. Standard caveats apply: off-planet trading has to be possible and cheap enough to allow a profit. If there are no such things as FTL starships, the customers will probably be asteroid miners or other group in the same solar system. With FTL customers can be anywhere in the galaxy.
The standard trope is as a world becomes more industrialized and urbanized, its native agricultural sector shrinks and the world becomes more reliant on food imported from farm planets. Sometimes such planets are called "breadbaskets", "rice bowls", or other name based on a food staple.
A variant is when the planet has an agricultural product which is not food, but is [a] valuable and [b] does not grow on other planets for some odd reason. An example is the wonder fabric fiber "Kyrt" from Asimov's The Currents of Space. Another is the tree moss pseudofistus thalopsis on Plattner’s World featured in David Drake's Paying the Piper. From it can be extracted the raw ingredient for Thalderol, an anti-aging drug.
A variant on agricultural worlds is a world with a native plant which produces an intoxicating drug. In SF novels for unexplained reasons (because the author said so) the plant will only grown on that particular world. The drug is usually illegal, and the entire solar system the world resides in is totally overrun with drug-lords, drug-runners, and narcotics police. In extreme cases the entire world is interdicted; but where there is a will, there is a way in. No matter how many fleets of patrol ships blanket the world, the blockade runners manage to escape with narcotic cargoes.
When the drug is not the focus of the author's novel, the drug can be legal. Or not even that special. In David Drake's Counting The Cost, the main export of the planet Bamberia is tobacco. It has a slightly different flavor than normal, but it is still only tobacco.
An interesting variant on the drug-world is Tanith from Jerry Pournelle's CoDominium universe. Tanith produces the drug Borloi. But it is being cultivated and harvested by the CoDominium government, not the drug king pins. It seems that Terra has huge enclaves of welfare dependents, the government distributes Borloi to keep them from rioting. Somewhat similar to the drug Soma from Brave New World.
This is when the science fiction universe has some fantastically valuable handwavium mineral/drug/quantum-particle/whatever and of course there is only one planet in the entire freaking universe that has it.
Examples include Unobtanium (a room-temperature superconductor, not Unobtainium) on the moon Pandora in the movie Avatar, Stroon (or the "Santaclara drug", indefinitely delays aging) on the planet Old North Australia aka "Norstrilia" in the Instrumentality of Mankind series, and the spice Melange (prolongs life, heightened awareness, and unlock prescience) on the planet Arrakis in the Dune novels
On Pandora the interstellar expedition has an army armed with powered armor and milspec strip-mining bulldozers because they are not going to let a bunch of primitive indigenous aborigines stand between them and billion-dollar unobtanium.
On Norstrilia they know every crook in the universe wants to steal Stroon from them, so they have a powerful array of weapons including the dreaded Mother Hitton's Littul Kittons (don't laugh).
On Arrakis every powerful aristocrat wants to control Melange because people in general want to live forever and the Spacing Guild in particular needs it to safely pilot their FTL starships. The aristocrat houses are forever scheming and fighting each other for Arrakis. Whoever controls the spice, controls the universe.
The capital of the interstellar empire. Examples include Trantor and Coruscant. Both of these have cities covering every square centimeter of ground since you can never have too many bureaucrats when you are trying to administer a freaking galactic empire.
The Imperial Capital will be the biggest, and generally located in the center of the empire. Remember that Imperial reaction time limits the radius of the empire. The radius can be expanded by establishing secondary throne worlds called "sector capitals" near the limits of the central capital's sphere of influence.
Since throne worlds are the only thing maintaining control over the sector of the empire within the world's reaction time radius, they are targets for hostile action. Eliminate a capital (or even better, capture its bureaucracy), and you are well on the way to capturing an entire stellar sector. Since the Empire is not totally stupid; throne worlds are guarded by huge armadas of miliary spacecraft armed to their little pointy teeth, orbital fortresses bristling with weapons, extensive planet-based defenses, watchdog outposts, and far-flung combat scouts.
In the Warhammer 40k game, "Forge World" is the colorful term for a planet that is wall-to-wall factories, totally devoted to manfacturing machines and other goods. In other fiction such planets are usually devoted to the military-industrial complex, cranking out weapons, ordinance, and combat spacecraft.
Forge Worlds usually do not exist outside of space operas, since it is a one-product planet. In reality a planet with a bit of industrial capacity will often accept a few military contracts.
A Penal Colony or Prison Planet occurs when somehow it is cheaper or more politically expedient to ship prisoners to an interstellar colony instead of putting them in local jails. The technical term is penal transportation. In theory the transported can return home when their sentence is up, in practice that never happened.
Sometimes colonies are "dumping grounds for undesirables." From 1788 until 1868 Great Britain shipped over 200,000 criminals and the bankrupt to the 13 colonies in North America (surprise!) and Botany Bay colony in Australia. Virginia and Pennsylvania passed laws to prevent England from dumping the convicted in the 13 colonies, the King of England condescendingly told them where they could stick their pathetic little laws and kept dumping. The dumping only stopped after the American Revolution, which is why England started sending the convicted to Australia.
Penal colony planets are usually miserable hell-holes. The prisoners may or may not be forced to perform hard labor (often mining), if no labor is required the government thinks that the hardship of simply living on the planet is punishment enough. The morality become questionable if the prisoners start to have children, who then are being punished for the sins of their parents.
In Jerry Pournelle's Falkenberg's Legion novels, initially quite a few nice planets had nice colonies established. But the mounting population on Terra threatened collapse of civilization. So the Bureau of Relocation (BuRelock) would periodically perform sweeps through the welfare island districts and ship all the undesirables off to dump in the colonies. Whether the colonies wanted them or not. The nice colonies became not quite such a nice place to live, trying to cope with the unexpected flood of undesirables. But Terra has all the guns so shut your mouth.
Cult Colonies happen when a group of fanatics actually manages to form an Extremist Settlement. By definition the colonist's culture is outside of Empire societal norms. They can be quite uncomfortable places to visiting outsiders.
An Imperium-imposed Colony Educational Service team can try to prevent things from going too far downhill. Good luck with that, such a team is by definition "outsiders."
A Lost Colony is when somehow a colony loses all of its technology, and Terra loses all record of the colony's existence. The colony reverts to whatever technology is supportable (probably about pre-Industrial Revolution), and may even forget that they are not native to the planet. In pulp science fiction, writers were fond of using the shocker that Terra itself was a lost colony from somewhere else (a couple of such pulp stories also threw in a gratuitous "Adam and Eve" theme). This fell out of favor when evolutionary science had advanced to the point where it could demonstrate that mankind almost certainly evolved on Terra.
The part about Terra losing all records of the Lost Colony can happen many ways:
- Terra can suffer a nuclear war (which the lost colonists might have been fleeing) thus destroying all the records
- The colonists are founding a Cult Colony and carefully destroy all records of their destination before leaving
- The colonists use a sleeper ship aimed at random which after a few thousand years happens upon a habitable planet unknown to Terra
- The colonists use an experimental faster-than-light starship which malfunctions and lands them in a location unknown to them or Terra
- Or any combination of the above
When contact is reestablished with Terra, what happens next is influenced by which of the two has the higher technology.
An amusing twist is when Terra is the lost colony.