In the near future humanity has started mining on Mars. International (and interplanetary) treaties governing the use of lethal weapons in space dictate that anyone possessing such a weapon must carry a license.

However, every spaceship, including single-occupant vehicles, carries some sort of ranged personal firearm.

There is no danger of being hijacked or abducted in space, since only established major companies and wealthy nations can afford any kind of space program. For security reasons all spacecraft personnel have to go through thorough screening and checks before being permitted to go into space to ensure that they are unlikely to cause harm to themselves or others.

With all this in mind, what good reason is there to have a personal lethal weapon(gun) in a spaceship?

(Additional assumptions: no aliens - SETI called, nobody answered - and no faster-than-light travel.)

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – James
    Commented Feb 28, 2019 at 18:04
  • $\begingroup$ Some of the crew are security guards. They may have to arrest or detain other crew members. $\endgroup$ Commented Apr 24, 2022 at 2:12

19 Answers 19


For the same reason some do in real life. Ship (or landing pod) landing isn't perfect so when they arrive back on earth the astronauts need to defend themselves against hostile animals or scavengers.

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    $\begingroup$ In Svalbard, you are basically told to bring a gun if you're heading outside town due to the danger of polar bears. $\endgroup$ Commented Feb 25, 2019 at 9:19
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    $\begingroup$ @Spoki0: Not just "told to", AFAIK it's required by law. youtube.com/watch?v=ch7HwhGynXk a bit off-topic here though. $\endgroup$
    – Nyos
    Commented Feb 25, 2019 at 9:23
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    $\begingroup$ @Nyos sysselmannen.no/en/Shortcuts/Firearms It is not required to carry a gun specifically, just recommended. Point is that you might crash land and need to defend yourself, as the answer stated. If you happen to land on Svalbard, you'd be a criminal if you didn't have the means to chase off polar bears! $\endgroup$ Commented Feb 25, 2019 at 9:51
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    $\begingroup$ @ErosRising not on Mars, sure, but if they are bringing the minerals back to earth for processing, this scenario can happen. $\endgroup$
    – Aserre
    Commented Feb 25, 2019 at 16:54
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    $\begingroup$ @ErosRising And it's easy to explain as "part of a mandatory basic survival kit". Early on a law is passed that all space craft carry a survival kit just in case they land in some remote location on Earth and need to get by for a week until they are found. Time goes on and they start traveling to Mars regularly, but the law is never changed, and why remove it just because you're heading to Mars. It's just easier to leave them alone since there has never been a reason to mess with it. It's just another piece of equipment like a hammer that is only pulled out for maintenance by port authorities. $\endgroup$
    – AndyD273
    Commented Feb 25, 2019 at 19:11

Warning: Dark

Imagine a situation where you're in your spaceship, you've run out of fuel, your comms are down, and you're flying through space away from civilisation.

You may have rations to last a few weeks, but with every passing hour, the chance of rescue gets slimmer and slimmer.

After a few days, you know there is no hope of anyone finding you.

You reach across to your firearm...

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    $\begingroup$ Environmental control is less painful, although not as fast. Disable the oxygen scrubbers and let CO2 build up in the cabin until you pass out. $\endgroup$
    – Cadence
    Commented Feb 25, 2019 at 9:13
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    $\begingroup$ Cue "Major Tom" $\endgroup$
    – Martijn
    Commented Feb 25, 2019 at 9:13
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    $\begingroup$ ... and use the recoil of the firearm to propel your ship and plot an encounter with a planet ? $\endgroup$
    – Goufalite
    Commented Feb 25, 2019 at 13:48
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    $\begingroup$ Breathing pure nitrogen would be a better way to go. A build-up of CO2 will lead to a feeling of suffocation, whereas replacing O2 with N2 leads to death with no sense of oxygen starvation. $\endgroup$
    – Dancrumb
    Commented Feb 25, 2019 at 14:24
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    $\begingroup$ For a minute I thought you were describing the lead-up to a CANNIBALISM situation :D $\endgroup$ Commented Feb 26, 2019 at 12:53

No good reason for purpose-designed firearms

Risk assessments are critical to space travel, even more than on Earth. Some of the obvious things that can go wrong because you are carrying a firearm are:

  • propellant becomes unstable
  • poor maintenance results in mechanism seizing up
  • accidental/negligent discharge results in personnel injury or death
  • accidental/negligent discharge results in destruction of critical spacecraft components (including atmospheric integrity)
  • accidental/negligent discharge imparts momentum (linear or rotational) to spacecraft requiring fuel expenditure for course correction

In addition to these possible risks there is also the certainty that every single flight will be wasting mass on a dangerous object of negligible use - mass that could be used to carry more fuel or operational/profit-generating payload.

To offset these massive disadvantages, there has to be a concrete benefit to putting a firearms on a spacecraft. This is hard to see - in the anti-hijacking role weapons such as tasers are much preferred to things that punch holes in your own ship. Boarding actions are dubious in any hard science setting - docking with a cooperative target is hard enough, docking with an uncooperative target is practically impossible even if its propulsion systems are disabled. As for employing firearms (other than those mounted in sophisticated turrets) against other spacecraft - forget it. Then there is the problem of keeping all of the astronauts current in their firearms training - if they are rusty then they may as well not have a firearm.

But wait...

Not all is lost, however. As was well-portrayed in The Martian, astronauts are a technically competent group of trained improvisers. If the plot of your story requires that a firearm is used then a character can improvise one. Hand-held and/or drone thruster units are a plausible item to have on board a spacecraft - if you disconnect a few safety devices and plug the exhaust with a ball bearing (possibly with some tape wrapped around it to get a good seal) then you have a projectile weapon. A high-pressure air tank is a ready-made reservoir for a very dangerous air rifle, just add a metal tube for a barrel and a valve. (With more time a semi- and/or full-auto version could be manufactured.)

If the requirement is just for a ranged weapon, not necessarily a firearm, then slings are just as easy to make as on Earth. A spacecraft machine shop could be used to make a bow or crossbow.

In summary - just as in many situations on Earth, carrying a firearm is far more dangerous than not carrying a firearm. However, spacecraft have plenty of options for making ranged weapons in an emergency.

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    $\begingroup$ Idk in what world firearms in the hands of trained users acting as their training tells them to are more dangerous than improvising weapons from thrusters. $\endgroup$
    – Giu Piete
    Commented Feb 25, 2019 at 8:55
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    $\begingroup$ I think the point is, that you don't bring anything to space without reason. So if there is no reason to bring a gun, then you don't. But if the plot requires you to have something like a gun, then you can craft one out of stuff you have with you (originally for other purposes) $\endgroup$ Commented Feb 25, 2019 at 9:00
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    $\begingroup$ +1 for pointing out that actually using the gun in your spaceship is a good way to experience decompression via a perforated hull. $\endgroup$ Commented Feb 25, 2019 at 13:01
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    $\begingroup$ Modern powder doesn't just "become unstable". Nor do modern firearms just "seize up" after periods of disuse in clean environments. Your points about negligent discharges and weight are valid however. $\endgroup$ Commented Feb 25, 2019 at 15:38
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    $\begingroup$ dv'ed for the reliance on negligence. A gun on board a craft would likely be kept in a lockbox, or case, with magazine completely separate from the gun. It would be pulled out when needed and put back when its use is no longer required. Powder doesn't just suddenly become unstable nor do guns just stop working. Some are even prized for their ability to just work even in the crappiest of circumstances. $\endgroup$
    – Hueco
    Commented Feb 27, 2019 at 19:55

One potential explanation (although not 100% satisfactory) is that it could form part of a survival kit. Bomber pilots, for example, were often equipped with survival kits including flares, emergancy rations and rifles such as here and here, to help them forage for food and protect against wildlife should they crash land in remote areas. This could feasibly also apply to a spaceship, should they crash land on a remote part of earth.


I can't find the exact quote, but there is a saying in Science Fiction which goes something like this:

Any feasibe method of space propulsion is indistinguishable from a weapon of mass destruction.

Invent a propulsion system which is very easy to weaponize. Make sure that it is infeasible to modify it in a way that it can no longer be used as a weapon but still work as a propulsion system.

  • If you are still using chemical propulsion, the exhaust can be weaponized.
  • If it's a nuclear thermal rocket, the exhaust is not just hot and fast but also deadly radiation.
  • If it's a plasma propulsion engine, it shoots a ray of highly energetic plasma.
  • If it's nuclear pulse propulsion, you have an arsenal of nuclear warheads on board.
  • If it folds space, it can shred other ships to pieces through sheer forces.
  • If it is based on artificial gravity, you can literally "crush your enemies" or rips them apart.

Benign technologies which can be easily weaponized are also a recurring theme in Larry Niven's Known Space universe. Among them are afore-mentioned weaponized propulsion systems are laser-based communication systems (which are powerful enough to cause space ships to overheat) or an alien digging tool (which also digs nice holes into metal plates).

I personally like the communication lasers, because communication is too important to declare illegal and you can aim them independently from your engines.

  • $\begingroup$ I think you're halfway there. You've established that spacecraft can be dangerous, but not how including a weapon addresses the danger. Furthermore, it's not clear from the OP whether a "ranged weapon" means a handgun/rifle, or a shipborne artillery piece. $\endgroup$ Commented Feb 25, 2019 at 17:26
  • $\begingroup$ Good point about the quote, it remembers me the 3rd law Arthur C. Clarke. However, I don't understand how this is related with fire gun (I mean, pistols, gun, rifles and that stuff which the OP is asking about). $\endgroup$
    – Ender Look
    Commented Feb 25, 2019 at 18:32
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    $\begingroup$ I too thought the quote was from Niven, and sure enough, a bit of googling turned up the Kzinti lesson: "a reaction drive's efficiency as a weapon is in direct proportion to its efficiency as a drive." $\endgroup$
    – Sterling
    Commented Feb 26, 2019 at 4:59
  • $\begingroup$ Properly-functioning NTRs don't have radioactive exhaust (except for some open-cycle gas-core designs). $\endgroup$
    – Vikki
    Commented Feb 28, 2019 at 4:26
  • $\begingroup$ If it folds space, wouldn't the other ship be unaffected? The other ship would just move the same way the space does $\endgroup$
    – somebody
    Commented Feb 28, 2019 at 5:05


Due to security reason all personnel have to go through thorough screening and checks

These checks do not end all of the possible security issues. They just ensure that a single individual or ar small group does not pose a significant threat.

But what if a group of individuals become the threat? Physical force is still a thing, and if a number of individuals mutiny or revolt, they could be dangerous, either by attacking the loyal crew or accessing critical parts of the ship.

Not to mention that people can become very imaginative when it comes to improvised weapon design.

To put an example, we already have places were people are very careful screened to avoid them inserting weapons in a controlled environments. Yet improvised weapons are made (shivs and the like), revolts do occasionally happen, and the guards do have weapons and/or have support from armed security forces readily available.

Imagine the situation in a spaceship where external support is not available and everyone on board knows about it.

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    $\begingroup$ Also, no "screening and checks" can really "ensure" anything, merely make it more difficult for people with bad intentions to get through. All it takes is one thief or spy or traitor to cause a great deal of damage, if everyone else is helpless. $\endgroup$
    – workerjoe
    Commented Feb 25, 2019 at 15:46
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    $\begingroup$ More uncontrollably, no amount of screening will guarantee that your intrepid crewmates won't eventually fray under sustained pressure, or take a personal tragedy badly, or find themselves faced with an impossible conflict of interest $\endgroup$
    – Pingcode
    Commented Feb 26, 2019 at 10:37
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    $\begingroup$ Screening takes part before launch. But what if spacecraft of one "wealthy nation" assaulted the spacecraft of another "wealthy nation" mid flight or on Mars? Gotta have a way to discourage and/or prevent a successful abordage. $\endgroup$
    – user31389
    Commented Feb 27, 2019 at 14:11
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    $\begingroup$ @Pingcode: Or just go mad from being stuck in a spaceship day in, day out. $\endgroup$
    – Vikki
    Commented Feb 28, 2019 at 4:28

If you are not worried about Earth Wilderness landing like Leo Adberg has suggested (which is a very good real world answer), then an alternate would be to consider corportate/national espionage...

If there are only the biggest corporations and governments in space then its safe to assuming there is no space police, so if one company decided to hijack another's ship to either steal the presumably cargo, or possible find out what tech the rival company is working on, then its safe to assume the pilots would want to protect themselves.

Writing in that either companies or governments are in a type of cold war as to who can be the front runner in space travel and its not unreasonable to believe that with all the communication dead zones are the system (dark side of the moon for example, at least until china sent there probe a few weeks back) and there's plenty of areas where a ship could get be hijacked without anyone knowing.

Thankfully we've managed to avoid taking warfare to space so far but its not exactly out of character for the human race to do so...


There's two possible reasons I can think of.

The first is for some sort of emergency situation - much like trains have hammers to break the windows in an accident - perhaps there could be some situation where they'd need a weapon (are the weapons traditional current conventional weapons?) to break free of a crashed pod or something? Certainly you could argue the carrying of flare guns for situations like this - as safety equipment

The other is if there are any tensions between the big companies and/or wealthy nations. They could then be argued as necessary to protect a claim on a certain sector. Perhaps there had been an incident in the past where one company took over another, so they all carry an stock of weapons for protection against this. (easy to argue it's similar to countries on earth with weapons that are they will never use)

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    $\begingroup$ +1 for flare guns. Instead of simply being single-use, they could have a "weapon" mode just in case. $\endgroup$ Commented Feb 25, 2019 at 22:06
  • $\begingroup$ Or it could be that they need a sort of emergency cutting equipment (in case of a crash or something) like an oxy-acetylene torch (or a laser cutter?) that could be fashioned to be a ranged weapon somehow ? $\endgroup$
    – Smock
    Commented Feb 26, 2019 at 11:17

You never know if a person may become mad or commit a crime on board. Space is exhausting, that can happen.

The captain and security must have weapons to arrest, take down or kill that person. Also, that gives authority to them, useful if there is unrest on the ship.


There used to be a good reason, so it was written into law and no-one has bothered to change it. Or maybe it's a religious thing.

See https://www.telegraph.co.uk/news/uknews/1370385/Navy-up-in-arms-over-challenge-to-sword-protocol.html for inspiration.


Well, it could be for quite innocent reasons, such as blasting asteroids out of your way. There's no knowing when you might come across these floating menaces; they can wreck your spaceship all the same, especially if your spaceship's too bulky for maneuvering out of the asteroid's way, or if you're passing through an Asteroid Belt, and wiggle-room's very limited.

So having a heavy-duty Vaporizer(?) equipped on your spaceship is never a bad idea.

Another reason is Space-Pirates. Supposing it is the Wild Wild West era of Space-travel, plenty of lawless pirates abound the expanse of space.

So, hey, you can never be too cautious. You gotta have that weapon, dude.


It's a multipurpose EveryDayCarry power tool... steeped in politics.

Both in established areas, and - especially - out on the frontier, you often need to do certain tasks quickly, without advance notice. Time is money, and so is storage space.
So you carry compact tool to to mark things from a distance (paint), use force (slug), perforate/crack/attach (nail), signal (flare), attach beacons to inaccessible points... you're probably not on Mars to do accounting.
A set of specialized tools is not feasible - if needed on a larger scale, you send a team with the equipment. For small tasks, anyone on site will be able to do it with what they already have.

That it is also a very good weapon, is not just a nice bonus, it actually decided the form factor. After all, where surveillance is spotty to say the least, rival corps stake claims, and you're surrounded by people with at least mild cabin fever... it makes you feel a bit less helpless.

Plus, a whole new political power has arisen around the "weapon control" angle - by law you need a licence for firearms, by regulation you need firearms to go to space, by convenience you need the tool to work effectively... a body who can revoke those licenses is one to reckon with. The "need gun to travel" regulation is there to stay.


Shoot incoming space objects.

Inspired by https://www.cnn.com/2019/02/21/asia/japan-asteroid-sample-scli-intl/index.html

Space probe fires bullet into asteroid By Jack Guy, CNN Updated 6:11 AM ET, Fri February 22, 2019 Japanese space agency JAXA landed the Hayabusa 2 probe on the surface of an asteroid. Japanese space agency JAXA landed the Hayabusa 2 probe on the surface of an asteroid. (CNN)A Japanese space probe has successfully fired a "bullet" into an asteroid as part of a mission to collect rock samples from the celestial body.

The projectile disturbed material from the exterior of asteroid Ryugu which then floated from its surface due to the weak gravitational field.

Impacts with meteors are a threat to any spacecraft. A rifle is a good way to impart kinetic energy into some incoming mass. The firearm aboard spacecraft is very similar to a sniper rifle. If the computer alerts you to an incoming mass on a collision course, rather than expend fuel to alter your own trajectory it may be more expedient to shoot the incoming mass and alter its trajectory. It might take more than one shot.

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    $\begingroup$ This is a great answer. In a hard sci-fi setting, where space debris is common and hulls are flimsy, someone "sweeping" your path might be a necessary position. Then carrying a firearm isn't some luxury or throwback affectation, it is a vital part of the job. This could happen in different places depending on the tech level. Setting your spaceship into a common planetary orbit would be the best place for this. They tend to be littered with junk IRL and the relative velocities would be something a human could handle. Extra points if they are using an energy weapon to vaporize the trash. $\endgroup$
    – Solocutor
    Commented Feb 27, 2019 at 17:23
  • $\begingroup$ There was a video game about that. en.wikipedia.org/wiki/Asteroids_(video_game) $\endgroup$ Commented Feb 27, 2019 at 20:09
  • $\begingroup$ @Solocutor - I did not picture a guy riding shotgun with a radar visor and a Kentucky rifle with a 3 meter barrel. I do now. $\endgroup$
    – Willk
    Commented Feb 27, 2019 at 22:40

Space Rats!

Huge freakin' space rats immune to poison and too smart to eat cheese off a loaded spring trap. Too big to stick to a sheet of cardboard with glue on one side too.

It's either shoot 'em or trick 'em into going into the airlock.


Apart from utilitarian purposes (which would warrant something other than a weapon) there are 4 possibilities:

  1. Defensive - Internal threat
  2. Defensive - External threat
  3. Offensive - Internal target
  4. Offensive - External target

For #1 and #3, violence is the last resort of incompetence. One would hope that astronauts are intelligent enough to solve their problem by other means. Even if less competent people are allowed onboard and violence does become a means to solve an issue, weapons will only accelerate and worsen the outcome. If we concede that human nature is not going to mature beyond this primitive form of resolution, weapons merely level the playing field between humans of varying physical strength. They bring no improvement on the problem. So I would say they are not needed.

For #2 There could be a number of non-ET reasons to have a defensive mechanism for threat to the ship itself (e.g. meteorites, debris, pirates)

For #4 There would be good reasons for the "pirate" ships to have external weapons. This becomes a justification for #2 but because there are other reasons for #2, it boils down to the intentions of the people running any ship with external weapons.

in short:

  • Weapons inside the ship : NO
  • External weapons : Probably YES (or something that could be repurposed as a weapon)

In space, accidents happen.

Just start some rumor, that space pirates/aliens/spies (or whatever fits your story the best) are responsible for those accidents (like missing people/spaceships). Until the investigations are closed and the results satisfy your astronauts, everyone starts to carry firearms "just in case". You can make those investigations really long, or maybe the custom to carry can stay.

You can also make one legitimate incident, where some madman started attacking his coworkers, and blame guns on him (shootings happen on Earth all the time), also an incident like this might be the best reason to introduce those checks in the first place.

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    $\begingroup$ On the "legitimate incident" paragraph: the reverse is more likely, with weapons being banned from the ships. Despite a number of deaths and attempted murders at Antarctic bases, no one has started equipping them with guns. Instead, the Russians banned chess. $\endgroup$ Commented Feb 25, 2019 at 13:06
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    $\begingroup$ @Chronocidal: Good point! But there are countries with high crime and restictive gun laws, low crime with few guns, low crime with lot of guns, and high crime rates with guns. Also, the attitude towards guns have an effect on the crimes committed as well (without guns available, there won't be many gun-related crimes, but more crimes that could've been prevented by an armed bystander/victim). If Russia had more liberal gun culture, that would influence their attempts to protect themselves, whether they're in a research station or a spacecraft. I think choose whatever fits the story the best. $\endgroup$
    – Nyos
    Commented Feb 25, 2019 at 13:27
  • $\begingroup$ Well, the Americans didn't start taking guns to McMurdo after one of the Chefs attacked two others with a hammer in 1996 - so "liberal gun culture" doesn't seem to apply. (Of note: both Outer Space and the Antarctic Circle - south of 60° - are currently the subject of treaties that restrict firearms or military presence, which is why I consider it to be a good comparison. The treaty would need a reason to be reworked first.) $\endgroup$ Commented Feb 25, 2019 at 13:37
  • $\begingroup$ I think you pointed out perfectly why Americans didn't bring guns there. In OP's world that treaty has to be dealt with as well if he wants guns in space. But that's another matter. Also, the US is divided on this issue, more or less along party lines. So that also explains the lack of guns. But thanks for that, it's a valid point that needs an explanation if OP chooses this route. $\endgroup$
    – Nyos
    Commented Feb 25, 2019 at 13:56

Everyone may like the treaty and have good intent, but that's very different from trust. It's the same reason every good guy in the wild west had a people-shootin' pistol and the quickest trigger finger: because everyone else already has one. You don't have to have one, but it helps you sleep soundly knowing it's there.


I think I read this request as more of a "what excuse can I find for having a weapon on board" and not so much the reason for why one would have it on board at all. Like your story depends on there being a weapon when you have no logical reason for it being there in the first place.

Let's look at it from a corporate greed level. Suppose you were a massive arms producer and you wanted to ensure the next generation of interstellar networks all carry your brand and are guaranteed a minimum purchase value of $xxx for the latest interstellar security administration approved firearm on every vessel in active service - both private and other. Lobbyists go to work, somehow it gets on a ballot, and yay, it's approved. Interstellar violence can now proceed as planned and profited.

So now, even small rental space station travel vehicles are required by law to have at least one approved weapon on board for "security reasons" and loh and behold, you now have a gun for use in your story where there would otherwise not be one. Even in an automated vending machine restocking vehicle. If a human CAN travel in it, it has to have a weapon on board. By law. Yay the power of greed!


This sounds more like "I need my characters to be able to get a weapon off a spaceship without having a license" than any coherent world.


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