I've been exploring the idea of an interstellar penal colony or prison planet from a realistic perspective. This idea is featured in many science fiction stories, but I've never really thought deeply about the concept itself. Let's assume ftl travel exists. Does it make sense for a society to send its criminals to an isolated planet as punishment for a crime? If you want to get rid of certain criminals would it make more sense to execute them rather than spend the time/effort to transport them interstellar distances?

I would like to hear what others think. There are a couple scenarios that make a prison planet/colony seem worthwhile to me:

#1 - Space Australia. As a cheap way to set up a colony from scratch, a population of convicts is dropped off with tools and basic building supplies. They build shelters, set up sustainable food production, maybe basic industry. They would do this to contribute to their own survival with no input from the outside. At some point the society that sent them there would come in to take over a functioning colony. If the initial effort fails, just send more convicts.

Pros: No extra expense after the initial investment (Unless more convicts are sent). Low risk/high reward. No possible escape (Assuming people and supplies are dropped from orbit and ships never land).

Cons: This could only be a life sentence. Moral questions about what to do with children of convicts. (I guess you could have separate all male and female prison planets to avoid this issue?)

#2 - Prisoners sent to an existing colony for labor.

Pros: Allows for sentences for terms other than life. Provides an additional labor force to a developing colony.

Cons: Potential for harm to the civilians of the colony. Continuing expense (guards, facilities, control methods).

There are other scenarios featured in science fiction that I personally find to be pretty unbelievable. For example, the whole Riddick, Butcher Bay prison planet idea where the worst of the worst are sent. To me this is just Space Alcatraz. Why build and staff a prison on a planet completely by itself? Real Alcatraz closed because it was too expensive to constantly ship food/supplies/people all the time. Guards and staff would have to be rotated out or it would be just as much a punishment for them.

Maybe the whole idea is unrealistic and the only real solution would be a traditional prison on Earth or another settled world? I'm sure there are other scenarios that I haven't considered.

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    $\begingroup$ How difficult is interstellar travel in this universe? $\endgroup$
    – Cadence
    Commented Jun 5, 2023 at 23:51
  • $\begingroup$ Hello @bamjo, welcome to Worldbuilding. it's important that you understand the limits of this site. (a) Per the tour, Stack Exchange is not a discussion forum. This is not a place to "hear what others think." Stack Exchange's purpose is to help people find solutions to specific problems. (b) The help center specifically prohibits providing your own answers and asking for more. Given SE's purpose as previously stated, you already have solutions and don't need our help. We only allow you to provide your answers ... (*Continued*) $\endgroup$
    – JBH
    Commented Jun 6, 2023 at 3:19
  • $\begingroup$ ... when the don't work along with the specific reasons why they don't. This makes them limits and restrictions for answers - and the reasons you give explanitive conditions. (c) Finally, please note that people asking for factual explanations for fictional ideas has generated some frustration. To be frank, why such colonies exist has much more to do with narrative necessity than any practical physics that we don't yet understand. $\endgroup$
    – JBH
    Commented Jun 6, 2023 at 3:23
  • $\begingroup$ Basically, Australia, but in space =) $\endgroup$
    – Alastor
    Commented Jun 6, 2023 at 4:45
  • $\begingroup$ There are fictions that use prisoners as gladiators for entertainment/gambling (Marvel's Mojo, Deadman Wonderland). With gamblers from many galaxies it could be enough revenue. $\endgroup$
    – KC Wong
    Commented Jun 6, 2023 at 5:42

8 Answers 8


Penal colonies are for minimum security prisoners

The problem with most fictional penal colonies is that people assume that they are where you send the worst of the worst, but they actually have it backwards. Historically, most penal colonies have been places you send people who've done crimes too small to need to worry much about. Violent offenders, career criminals, political enemies etc. make a lot of sense to execute or keep in high security institutions, but penal colony prisoners were generally people arrested for non-violent, non-seditious crimes like counterfeiting, defaulting on debts, smuggling, tax evasion, working without a license, poaching, vagrancy, etc.

In fact, as the demand for workers in your colonies grows, you will likely outpace your ability to find legitimate criminals; so, you will generally see your government go down one of two unethical rabbit-holes to solve the problem. They will either become very strict about minor legal infractions or they will criminalize some minority group as a matter of policy to try to chain-gang as many prisoners off to the colony as possible; so, as the colony grows, you may see an increasing number of colonists who've literally done nothing wrong being shipped off like slave labor to try to fill demand.

Because they tend to select for people who've committed only minor crimes, penal colonists tend to not need a whole lot of special care to control compared to a normal colonial population. With nowhere for the colonists to go, you really don't need a prison system. They rely on you for survival, and most of them are not blood thirsty enough to fight back over long hours or poor work conditions. So they do their jobs, they live their lives, they raise their families, etc. The fact that there are children born out on theses penal colonies is actually in the interest of your government because the goal is to develop the planet. That takes workers; so, even if children are born here, the living conditions are humane enough that living here is seen less as an active punishment, and more as just a way to find a use for the dregs of society. So if children are born into the system, the government tends to not see this as a moral dilemma... even if it does in practice mean being born into serfdom.

Penal Camps can be an alternate form of execution

A lot of the confusion comes in the from of penal camps, which are distinctly different than penal colonies. Penal colonies are places people live. They spread out building roads, farms, homes, factories... everything you'd find in a normal settlement, but built by the hands of convicts instead of freemen. Penal camps are smaller. They are specific mines or industrial compounds built inside of a typical prison facility complete with guards, jail cells, etc. They are small enough in scope to double as a labor camp.

Penal camps are often places where the work is so hazardous that you use them as a form of death sentence. Examples of this would be the lead mines of Ancient Rome. Romans used a lot of lead for their plumbing, but they did not have the equipment to safely mine it; therefore they would invest heavily in security to guard a lead mine and keep prisoners from escaping, and force them to work where the lead would eventually kill them (6 months to 2 years on average). Because the hazards of lead were too well known for demand to be met with paid labor, the cost of building and maintaining a penal camp off in some remote place was well worth the investment.

This is where Sci-fi often goes wrong is that they try to justify remote penal camps. In the future, there is really no probable hazard where you would have a human do the work instead of a robot. The Romans built Penal Camps because they had no alternative for getting the lead they needed. A future society would find it much cheaper to use machines; therefore there would be no justifying a remote penal camp. Instead, if they make their prisoners do forced labor, it will focus on what is cheap, not what is dangerous; therefore any penal camps they have should be within normal established populations so that their stamped license plates or printed t-shirts or whatever you have them doing does not cost too much to sell because of transport costs.

World Building a Remote Sci-Fi Penal Camp

That said, a sci-fi remote penal camp can be done if you really want to.

To start with, you need a planet with a "Not Rare Over There" Unobtanium. This is important because it justifies bothering with a planet that has an exotic hazard instead of moving to any of the myriad other ones around.

This leads into the second step: This planet needs a hazard on it that affects electronics, but not the the human body. Something like powerful solar flares that periodically EMP the colony could work or maybe some native life form or grey goo that swarms and eats any sort of electronics you try to lower onto the surface. This forces mining of the Unobtanium to be done the old fashioned way with human labor and hand tools.

If you do this, then it suddenly makes sense for a space aged society to run a dangerous iron age style penal camp using convicted murders, rapists, insurrectionists, and targets for genocide, because without modern machines, the act of mining itself again becomes a death sentence.

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    $\begingroup$ the government might also find BS excuses to extend sentences, this has actually become a problem in modern for profit prisons. $\endgroup$
    – John
    Commented Jun 6, 2023 at 23:28
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    $\begingroup$ @John Opps, your lawyer used a blue notarization stamp page 17 of your release paperwork, but this year its's supposed to be a green stamp... I can't let you on the transport home this time, but don't worry, the next Class-F return transport will be here in 6 months, just get it fixed by then... oh that ship? That's a Class-S return transport. Those are reserved for returning smugglers, but this says you committed forgery; so, I can't let you on that one. $\endgroup$
    – Nosajimiki
    Commented Jun 6, 2023 at 23:48
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    $\begingroup$ More like, every time there is a hearing the prisoner is a violent antisocial likely to commit further crimes on release, whether or not its true. that or they pile one demerits for minor infractions which add up to an extended sentence. You forgot to shave otday that two demerits, you failed to meet your work quota 5 demerits, Complaining about your nutraloaf meal replacement that's a demerit, ect. But I like your idea for narrative bite. $\endgroup$
    – John
    Commented Jun 6, 2023 at 23:55
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    $\begingroup$ @AmiralPatate The reason to use a penal camp is not operating cost, but to fill labor needs that are too dangerous to be able to pay a freeman to do. The "Not Rare Over There" Unobtanium addresses the cost issue. A real world example of this could be Rhodium. It's so rare here near Earth's surface that the current going rate is over $200,000 per kg. If a large, pure Rhodium deposit were discovered in an Asteroid, then even a small mining operation could replace the entire 6.4 billion dollar per year industry... ie: enough to fund and profit from a deep space prison. $\endgroup$
    – Nosajimiki
    Commented Jun 7, 2023 at 13:56
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    $\begingroup$ @fredsbend: There are plenty of ways to execute criminals. The reason to use penal camps, specifically, is to accomplish whatever work they perform. $\endgroup$
    – ruakh
    Commented Jun 8, 2023 at 7:07

Does it make sense for a society to send its criminals to an isolated planet as punishment for a crime? If you want to get rid of certain criminals would it make more sense to execute them rather than spend the time/effort to transport them interstellar distances?


There's two main reasons why you put people in Prisons:

1: To punish them.
2: To remove them from the law-abiding population.

Think about the Death Penalty for a moment, regardless of your thoughts and feelings about it - it fulfills both of the two main functions perfectly. It certainly punishes them and it permanently removes them from the Law Abiding populace.

We (in the west at least, excluding America) tend to look dimly on the Death Penalty - miscarriages of Justice, squeamishness etc. etc.

However, for Crimes that are severe enough where permanent removal from society is warranted, then sending to a colony (where there is an implied 'no hope for escape') does have a lot of merit.

It's reversible (unlike the Death Penalty)
It solves the problem of a Prison break (or at least, adds such significant barriers to escape as to render it 'secure' in the minds of the populace)
'Out of sight, out of mind'

There are others - but that the rationale for why is not what you want to focus on:

What you have to contend with is what the populace in your story consider to be Ethical.

For example - for myself, I sleep very easily at night knowing that serial child molesters generally get severely assaulted/murdered in prison. There are those who say that when an individual is incarcerated, the State has an obligation to protect and provide them during their sentence.

Depending on what values your society holds will dictate whether or not they consider a penal colony to be ethical.

If they are more like me - then they will be fine with it, if they are more like the other group - they will likely not be okay with it.

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    $\begingroup$ Even in the US, the death penalty is mostly abolished. About 1/2 of the states have officially banned the death penalty, and even the states that allow it have very rarely enforce it in the past few decades. In recent history, less than 1 in 120,000 US prisoners have been executed. Saudi Arabia, China, and Iran are the only countries that still carry out executions as a common form of punishment. $\endgroup$
    – Nosajimiki
    Commented Jun 6, 2023 at 0:53
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    $\begingroup$ I agree with @Nosajimiki. In fact, over the last 20 years, there's been a distinct drop in executions. $\endgroup$
    – JBH
    Commented Jun 6, 2023 at 3:25
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    $\begingroup$ @Rekesoft There were 853 murder convictions in Japan last year... so no, still a very small fraction of major crimes are punished by death. en.wikipedia.org/wiki/List_of_executions_in_Japan shows that 89% of Japanese executions are for multiple murders. In the rare cases where a person is executed for a single murder like Tsukasa Kanda or Kaoru Kobayashi, the murder themselves demonstrate extreme predatory behavior and forethought. $\endgroup$
    – Nosajimiki
    Commented Jun 6, 2023 at 15:15
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    $\begingroup$ The real controversy about the death penalty in Japan is the secrecy with which it is done. In most countries, the death penalty is scheduled, lawyers are involved, facts are reviewed, etc. In Japan, execution is done at undisclosed times, and family, lawyers, etc. are informed after the fact that the person has been put to death. $\endgroup$
    – Nosajimiki
    Commented Jun 6, 2023 at 15:17
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    $\begingroup$ @tofro Not really. Rehabilitation should be one of the aim of a functioning justice system (along with reparation and protecting civil society from further harm), however you don't need to put people behind bars for that. In fact, prison is usually counterproductive to that effort. $\endgroup$ Commented Jun 8, 2023 at 5:53
  • What does interstellar transport cost?
    Right now, it would cost millions to send a person to Mars. If interstellar flight is even more expensive, penal colonies are a non-starter.

  • How complicated are new worlds?
    'Unsupervised' penal colonies work best if the world has a shirtsleeves environment. They do not work if it takes breathing gear, airlocks, etc., because maintaining those takes organized civilization.

  • What does the parent society think?
    In most societies, prisons are not the 'lock them up and throw away the key' style. They are supposed to reform inmates, and inmates are supposed to have at least a perspective of getting out. I write most, because some societies do seem to abandon reform.
    Spacelifting people is almost certainly more expensive than shooting them. Much more expensive. So one precondition for prison colonies, in the cinematic tradition, is a parent society where 'good citizens' like to pretend that they do have civil liberies, like not shooting offenders en masse, while in practice they give the offenders an one-way ticket to a faraway place.

  • $\begingroup$ Just a thought on your first point - if I use NZ numbers - right now it costs about $150,000 per year to keep someone in prison. For a 10 year sentence, that's 1.5 Million. For a 20 year sentence, 3 Million, for a life sentence (whole life, not a 'life' sentence) - assuming incarcerated at age 20 and died at 80 - that's about 9 Million dollars (assuming no increase in costs). A one time cost of a couple of million to save a lifetime cost can and could be cost effective. $\endgroup$ Commented Jun 6, 2023 at 20:44
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    $\begingroup$ @TheDemonLord it sure would be cheaper to just shoot them in the back of the head, and bury them in Potter's Field. $\endgroup$
    – RonJohn
    Commented Jun 7, 2023 at 0:51
  • $\begingroup$ If it would only cost millions to send a person to Mars there would be a city there already - there's a billionaire or two who'd be up for paying for it. (This doesn't affect your point in any way, I'm just pointing out that 'millions' is a huge underestimate.) $\endgroup$
    – N. Virgo
    Commented Jun 7, 2023 at 3:15
  • $\begingroup$ @N.Virgo, I'm assuming that there will be efficiencies of scale once we decide to ship many prisoners to Mars. The first dozen explorers will cost more per person than the next hundred, those will cost more than the next thousand, etc. $\endgroup$
    – o.m.
    Commented Jun 7, 2023 at 4:24
  • $\begingroup$ @TheDemonLord, so we'd have a bracket. From not-quite-recent numbers, the average sentence in NZ is about 1.5 years. So the ticket would have to be less than $225k to make shipping average inmates worthwhile, assuming they have no right to a return ticket after their sentence is up. $\endgroup$
    – o.m.
    Commented Jun 7, 2023 at 4:28

I think you may want to spend some time thinking about justice, punishment and rehabilitation. Your personal philosophy in these areas will give your story life. For permanent exile on prison planets, your society has a low to non-existent belief in rehabilitation. And that they're too squeamish to execute criminals. Or someone is making a lot of money from penal camps and has bribed politicians into making it a punishment for "undesirables".

For a "space Australia" scenario, there would need to be too many habitable planets - more than can be colonized. Additionally, fuel costs need to be cheap.

You may want to read a bit about the Tsarist & Soviet Gulag system. Many of the people sent to the prison camps were sent as political punishment. People who worked on significantly important projects (such as nuclear bomb design, or spacecraft design) did so from inside prison camps. I think a more interesting question would be what sort of people would perform such labor while imprisoned? What sort of people would trust the product of such labor?

In the book Provenance, there is a similar sort of prison planet system called "compassionate removal". It is poorly described, and most of the explanation appears as propaganda directed towards the society that exiles such criminals. It is pitched as a system for dealing with incorrigible and unredeemable criminals. One of the central characters was "rescued" from such a place. The little bits described show why the character is damaged.

Frequently, robots are stand-ins for slaves (with things like Asimov's 3 laws preventing slave revolts). Penal camps are not much different from slave labor. After the Civil War, chain gangs were a form of punishment to effectively re-enslave blacks. The predominant "crime" was called "vagrancy" which was the crime of not having a job. In some areas, county sheriffs became wealthy from renting out prison labor.


They sent about 162,000 British and Irish convicts to Australia between 1788 and 1868. The idea looks quite similar, so you might want to check why they did it.


Modern law does not punish

The notion of punishment is — literally — stone age jurisprudence.

Modern law exists for the following reasons:

  1. Protection Make sure the innocent are not subjected to crime.
  2. Prevention Make sure to take away the incentive to subject innocents to crime.
  3. Restoration Repair the injury to innocents, when they have been subjected to crime.
  4. Rehabilitation Repair the criminal, so that they do not do any more crime.

Punishment is retribution, i.e. state sanctioned blood vengeance. The only reason that still exists in modern law, is grandfathering.

So, would a correctional colony make sense?

Let us go through the four points.

  1. Does it provide protection? Yes, it does. However, there is only point to it is if the convict is likely to commit the same crime again.

  2. Does it provide prevention? A little bit, but being judged and sentenced does not do much to discourage people from committing crimes. And — again — this is on the assumption that the convict is likely to commit the same crime again.

  3. Does it provide restoration? It can do, if the correctional colony is manufacturing something that can go to the restoration of the victim.

  4. Does it provide rehabilitation? It can do, if it has some kind of treatment / programme that turns the criminal into a productive member of society rather than a criminal?

So, what would it take for a space colony to make sense as a correctional facility?

It would make sense for...

  • Repeat criminals...

  • ...that need to work off a debt for the damage they have caused...

  • ...and that are serious about trying to kick the habit and become productive members of society

It would also make sense for...

  • The incorrigible, the people that are so dangerous to society we simply cannot afford to have them among us any more.

This gives us two forms of justice colonies:

  • The correctional facilities, that let people work off their debt, learn skills and come back as better people

  • The people storage boxes, where we put those that cannot be corrected, at least not now.

So, does an interstellar prison colony make sense?

Yes, it does:

  • For repeat offenders that want to try to improve

  • For the ones that are truly dangerous and cannot be kept in civilised society



A space colony may be a place to send people deemed to be trouble-makers, if the society is authoritarian, yet sufficiently principled not to simply shoot these people. (Or, worried about making martyrs out of them).

So, there's a not very useful planet a long way away. "Troublemakers" are exiled there. It may be a Siberia, where they are not in general expected to survive. Or it may be perfectly habitable, just very sparsely populated and lacking any natural resources worth shipping between star systems.


Didn't the British do something like this when they sent people to Australia? They could have executed those criminals, but they didn't. We could follow a similar model.

It could go like this...

The earth is over-crowded and short on resources. The government recognizes that they need to get rid of people, but engaging in mass executions, limiting births, or letting the population starve are unpopular with the public.

At the same time governments have ambitions to establish off world colonies, but there are few volunteers who want to make a dangerous journey through space.

Citing an increase in crime and resource shortages, the government makes stricter laws. Then they use prison over-crowding as a pretext to send large numbers of people off world against their will.


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