So imagine a country so developed they have a space station in orbit around their home planet (nothing impossible here). That country decides to have a couple of soldiers (elite air force members) stationed there for security reasons. These soldiers are equipped with what amounts to armored spacesuits for protection. Now these soldiers are to have a firearm that they can even reliably use outside of the station in the vacuum of space.

Would a normal firearm suffice or would you need a specific type? (gas operated, recoil, blowback etc.)

  • $\begingroup$ What type of threat are these soldiers expected to face? Are they in place to defend against mutinies or other internal threats like boarding actions or are they in place to defend the station from exterior threats? $\endgroup$ – Dragongeek Feb 23 at 13:05
  • $\begingroup$ Primarily to protect the station from boarding or sabatage to the outside. For things like hostile spacecraft they have armed spaceplanes (spacefighters). $\endgroup$ – Blue Devil Feb 23 at 13:26
  • $\begingroup$ @BlueDevil spacefighters are like inadequate missiles, and will not fare well against people who use adequate missiles. $\endgroup$ – Starfish Prime Feb 23 at 13:39
  • $\begingroup$ In the world this takes place in there is quite a technology gap between most countries. The only countries in this setting capable of posing a credible threat to the space station are allied with the nation the station belongs to. Most others would either not even be able to get into space or would send aircraft there that once they enter the exosphere would struggle to even stay airborne let alone engage armed aircraft designed for operation in space. And as for long range missiles. Like i said the only ones who could build such a missile are allied to the station's owners. $\endgroup$ – Blue Devil Feb 23 at 13:47
  • $\begingroup$ @BlueDevil either there's no-one for the fighters to fight, making them useless, or there are people who are capable of making missiles that will easily outperform the fighters, making them useless. There's no middle ground there. $\endgroup$ – Starfish Prime Feb 23 at 14:00

Any of the firearm types we use now (bolt action, revolver, gas operated, recoil operated, or blowback) would function as expected in vacuum, with two significant caveats. According to "Gun Jesus" (Forgotten Weapons on YouTube), the Soviets sent handguns up with certain space missions, as well as mounting weapons on one of their early space stations. The guns they used appear (from the photos, I haven't seen the video) to be single-shot weapons, like a Soviet version of a Thompson-Center Contender, though from comments I understand they're semi-autos, descended or derived from the Makarov.

First, ammunition will need some level of special production to protect against air trapped inside a metallic cartridge from popping the bullet (or primer, but with less area it's less of a problem) out of the casing, resulting in various kinds of failures.

Second, the weapon itself (specifically the barrel, receiver or frame, and revolver cylinder) will need to be proofed for service in space (among other things, lubricants are likely to be an issue due to evaporation, lack of lubricants more so due to cold welding, and a weapon left in shadow for a prolonged period may reach cryogenic temperatures, which can weaken steel).

As pointed out in comments, if you fire a weapon enough times in rapid succession, the barrel and chamber will get hot -- and in vacuum, you don't have air to carry the heat away, you can only dump excess heat by radiation. I consider this a relatively minor problem, however; the only firearms that routinely have barrel heat issues that affect their regular operation are heavy machine guns (like a Browning M2 .50 caliber), firing large rounds at a high rate for a prolonged time. It's possible to heat up an assault rifle enough to melt or burn the wood or plastic parts, but this typically requires firing multiple full magazines (20 to 30 rounds each) in rapid succession. I wouldn't expect this to be a significantly larger problem in vacuum than at Earth's surface.

Assuming the weapon has been redesigned as necessary to work correctly with lubricant coatings instead of oils and greases, protect against cold welding, and stand up to high pressures at temperatures below 100 Kelvin, and the ammunition treated (likely by crimping both bullet and primer, as is already done for weatherproofing) to stay together in vacuum, then the only other issue is recoil.

This doesn't have to do with the weapon as such -- but a gun is essentially a pulsed rocket, with part of the exhaust being a solid projectile. Each time it's fired, it will push the user backward, and if the line of thrust doesn't go through the shooter's center of mass, it will also cause a spin or tumble (possibly violent enough to be difficult to stabilize with suit jets or similar). The only kind of weapon within our current technology that wouldn't have this problem, however, is a rocket launcher or recoilless -- which means your space troopers might finally provide a market and suitable need for the Gyrojet "rocket pistol" (and its carbine version).

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    $\begingroup$ Don't forget heat management: a barrel get's hot on Earth after sustained fire, and there is air to cool it. In space that would be gone $\endgroup$ – L.Dutch - Reinstate Monica Feb 23 at 12:54
  • $\begingroup$ If you're firing enough for barrel heating to be a big issue (in my experience, that's a dozen rounds or more for a rifle, several dozen for a handgun) with a conventional firearm, you've obviously solved the reaction tumble problem. The weight of barrels makes them great heat sinks, up to a point. $\endgroup$ – Zeiss Ikon Feb 23 at 13:05
  • $\begingroup$ To this day, Russian Soyuz capsules carry pistols (initially, Makarovs, then the specially-designed TP-82, and nowadays unspecified semi-automatic pistols) as part of the survival kit intended to be used on Earth after landing, if some mishap makes the spacecraft land in the wilderness. It all started with Pavel Belyayev and Alexei Leonov finding themselves stranded in Siberia, neck deep in snow in freezing temperatures; they were understandably worried about wolves, bears etc. $\endgroup$ – AlexP Feb 23 at 14:00

Not for Repeated Use

This has been investigated before! In addition to removing oxygen from bullets/cartridges, figuring out heat issues, reaction forces (just brace against something before you shoot), you still have the problem of getting space-grade lubricants on the moving parts.

You need special greases that will not evaporate in vacuum but also withstand the forces/heat generated by a bullet. Otherwise, a normal gun fires once or twice, but not in a repeatable or reliable manner. People generally use these greases for things like vacuum systems- which are usually room temperature or lower. I'm not saying such a lubricant doesn't exist, but it is not common!

The Gyrojet!

Each piece of ammunition is actually a small rocket that a solder would aim at the intended target. It was meant to be able to shoot in space. It mostly solves the head-dissipation issue by (mostly) keeping the head on the "bullet" and exhaust gases.

  • $\begingroup$ Suitable vacuum lubricants will of course be vastly more common in a future which involves significant human presence with mechanical devices in space. $\endgroup$ – Starfish Prime Feb 23 at 17:07

Missiles rule the day. The space station might be a sitting duck that could be hit by a bullet from ten thousand miles away, if your aim and your orbital mechanics are good enough. But whatever comes to attack the space station is almost certainly able to maneuver. So a weapon that can't steer to match that vessel's evasive action ... might as well have been left on Earth to save fuel. That is, unless the soldiers on the station have some matters of honor they mean to settle among themselves in archaic fashion.

  • $\begingroup$ I think the Rule of Cool is implicit here. Spacefighters were suggested as part of the setting, after all. $\endgroup$ – Starfish Prime Feb 23 at 13:56
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    $\begingroup$ Well, there's nothing cooler than a big space station blowing up... $\endgroup$ – Mike Serfas Feb 23 at 14:02
  • $\begingroup$ Can't argue with that ;-) $\endgroup$ – Starfish Prime Feb 23 at 14:03

As all the usual answers have been done already, I'm going to suggest a couple of slightly different things.


Rotary grenade launcher

Here's a grenade launcher with a rotary magazine. It has a number of potentially interesting features. It can take a wide variety of ammunition types, allowing the use of non-lethal riot-control type things inside space stations where shooting a big gun risks poking a hole in the world and letting all the air out. It can deploy smoke. Imagine what it would be like to be in combat in a spacesuit, and to have someone shoot a can of paint at you. You ain't gonna be wiping that off your visor with your big clumsy mitts. You're blind, utterly disoriented, and in short order, out of the fight.

More interestingly, though, it could do things like fire a proximity-triggered fragmentation round of the sort more commonly associated with anti-aircraft cannon.

Aiming and shooting weapons whilst wearing a spacesuit is going to be really hard. Anything that makes life easier for the shooter will tip the balance of the fight in their favour. Not quite shooting straight? Never mind, just get close enough and you'll hole your enemy and they will not be fighting much more today.

There are even more things potentially available here, including simple guided projectiles or small rockets. The sky has ceased to be the limit!

For related reasons, I'd also consider shotguns. Similar benefits, but the smaller rounds preclude the more exotic or destructive options that the big chunky launcher might offer.

There's a kind of shotgun ammunition you may or may not be familiar with, flechettes:

Flechette shotgun ammunition

These cartridges fire a bunch of aerodynamically stabilised darts, and are therefore minimally useful in a vacuum, but inside a space station they offer a way to penetrate spacesuits at a distance even without needing the sort of careful aiming that is difficult when wearing a spacesuit yourself.

Against unarmoured opponents, regular shot offers a similar benefit without the worry of letting all the air out of the habitat.

  • $\begingroup$ I would go with shotguns. I can imagine these being used less for fighting people and more to manipulate / deflect things at a distance. Related: worldbuilding.stackexchange.com/questions/139969/… $\endgroup$ – Willk Feb 23 at 15:27
  • $\begingroup$ And the shotgun myth rises again. A cylinder bore (no choke) will throw a shot column that's only a few inches in diameter at a range of 6-7 meters. The shot doesn't spread enough to call it a "pattern" until it's 20-25 meters away, even without a choke. Chokes exist in order to keep the pattern tighter for shooting at longer distances. $\endgroup$ – Zeiss Ikon Feb 23 at 16:50
  • $\begingroup$ @ZeissIkon um, what? I don't recall mentioning shotgun chokes, range, spread, pattern, or even barrel length. $\endgroup$ – Starfish Prime Feb 23 at 16:54
  • $\begingroup$ "without needing the sort of careful aiming that is difficult when wearing a spacesuit" -- you need to aim to hit anything with a shotgun. Your shot column won't be wide enough to obviate the need to aim even with spreader loads and no choke. $\endgroup$ – Zeiss Ikon Feb 23 at 16:58
  • $\begingroup$ @ZeissIkon a spread of several inches compares well with a gun that does not have a spread of several inches at a particular distance. Barrel lengths would be appropriate to the environment being fought in; there's no reason to have things the size of a polearm which provide a tight group of shot at a distance when the goal is to reduce the difficulty of hitting a target! $\endgroup$ – Starfish Prime Feb 23 at 17:03

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