In space, boarding parties could be used to effectively take over ships without severely damaging them. Piracy would be much easier. But what about weapons?

Your average pirate will have a slug thrower not some sort of marine ship safe laser. In a metal hallway bullets will ricochet a lot. With a 0g environment using ballistics at all is dangerous.

How can pirates exist due to the risks of ricochet? Is their anyway to board a ship and take it over using ballistics safely?

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    $\begingroup$ I don't think 0g will have much effect on ricochets. In close quarters, a ricocheting bullet will lose most of its energy by striking several surfaces in a very short period of time. In the fraction of a second between when the bullet is fired and when it comes to rest, gravity won't have sufficient time to have much of a noticeable effect on the bullet trajectory. I expect it would be pretty similar to a gunfight on a submarine. $\endgroup$ Dec 16, 2020 at 15:05
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    $\begingroup$ "boarding parties could be used to effectively take over ships without severely damaging them." Why? $\endgroup$
    – RonJohn
    Dec 17, 2020 at 4:47
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    $\begingroup$ "Piracy would be much easier." Why? $\endgroup$
    – RonJohn
    Dec 17, 2020 at 4:47
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    $\begingroup$ "Your average pirate will have a slug thrower not some sort of marine ship safe laser." Why? $\endgroup$
    – RonJohn
    Dec 17, 2020 at 4:48
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    $\begingroup$ "In a metal hallway bullets will ricochet a lot." Says who? (The walls of space ships will be really damned thin, to save mass.) $\endgroup$
    – RonJohn
    Dec 17, 2020 at 4:49

8 Answers 8


In an environment like a space station overpenetration and hull breaches are a greater concern than ricochets. The smart pirates deal with this in two ways. Encourage their targets to surrender without a fight, and use frangible rounds that break up on impact instead of continuing on as a solid projectile.

No-one wants a fight. Ammunition, and medical care are expensive and replacing experienced crewmembers can be difficult. If merchant vessels are given the option to avoid a violent boarding action by handing over their cargo it may be in their best interest to do so peacefully. Similar to how pirates operated in the 1600s and 1700s space pirates would leverage their fearsome reputations to discourage merchants from putting up an armed defense.


Some comments are suggesting massive rounds to knock the target back. I thought it might be helpful to compare the momentum of typical weaponry & a human:

  • 9x19mm; 0.008 * 360m/s = 2.8 kg*m/s
  • 5.56 NATO; 0.004 * 993m/s = 3.9 kg*m/s
  • .50 BMG; 0.042kg * 928m/s = 38.976kg*m/s
  • Human; 60kg * 1m/s = 60 kg*m/s

Only in Hollywood do guns knock the target back, unless you get into the anti-tank rounds, at which point getting knocked back is the least of your worries. These hypothetical pirates with massive rounds aren't carrying pistols or assault weapons, they're carrying artillery.

But that ignores the real killer for massive rounds, Newton's Third Law. Every action has an equal and opposite reaction. Any massive projectile capable of knocking back the target is also knocking back the shooter. The shooter must anchor himself against the wall to fire this beast of a weapon. But if the boarders are firing these weapons, then the defenders are as well, as well as anchoring themselves to the wall. As for an alternative suggestion, well, it depends.

From a worldbuilding perspective, pirate victims should surrender on sight (if they didn't, piracy would be too bloody and expensive to be worth it). From a narrative perspective, combat is exciting and we find reasons to include it, even if it's rare in the world. Perhaps the captain is too stubborn to surrender.

Which raises another point; combat should highlight character. Are the pirates clever? Then they're suited up on the outside, threatening to cut power and radiator lines. Are the pirates ruthless? Then they're shooting bullets inside the hull, regardless of over-penetration and hull breaches (fuel/oxidiser tanks explode, but mere hull breaches just slowly leak air; shooting guns inside a spacecraft is a very bad idea but probably not instant suicide). Are the defenders clever? Then one of them suited up, went outside, and has a knife to the power lines of the pirate ship.


In a microgravity environment everybody knows that momentum is a nasty mistress (or master).

Instead of firing lead/metal bullets, pirates fire gooey bullets, which splatter on impact transferring their momentum to the target without piercing it. If the target is hit close to their center of mass they will start flying backwards, else they will start spinning around. In both cases coming to a halt will be a struggle, allowing the pirates to have less nuisance while they do pirate things.

In case the bullet hits the walls of the place, it will splatter there, and a spaceship is much more massive than a human, thus won't be appreciably disturbed by it.

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    $\begingroup$ Won't the recoil be the same amount of force exerted on the pirates? $\endgroup$ Dec 17, 2020 at 0:28

Don't attack the crew, attack the systems

It might sound boring, but you probably won't attack the inside at all. Unless you go full sci-fi, the spaceships are most likely quite exposed with their systems. You'll attack life support physically or digitally. As an example, removing the air or changing the mixture can kill or incapacitate the crew, or make them move to safer compartments, essential locking them out of the rest of the ship. The moment they try to get out in spacesuits you'll cover those with certain weapons, killing or capturing them.

Whatever was damaged or changed might be easily repaired, leaving the spaceship and cargo largely in tact. This way you’ll minimise risk and maximise value.

Of course you can also go overboard and blow a door/segment to expose everything to the vacuum of space. But pirates, especially modern ones, are more economically astute than you might think. They understand very well they risk their lives and freedom by attempting this, so they often try to maximise profits. The risk/benefit is assessed greatly. Are you after highly valuable cargo that is able to survive in space? Blow half the ship and take the cargo. Is the value in the ship and crew? Spike the air and incapacitate them to take it over. You just don't want to get on a pressurised tube in space and actually battle other people.


sphennings's mention of frangible rounds is a great way to preserve lethal rounds while avoiding hull breaches. The use of intimidation and resource preservation to avoid a fight altogether is also very pragmatic.

Curtis brings up very good points about both Hollywood bullet momentum and suggesting shifting emphasis to characters.

Building on these answers and a few comments, I'd like to shift back to the technical aspects since you asked about "safe" use of ballistics.

Soft Projectiles

Recoilless weapons

Conventional projectiles' transfer of momentum to the shooter is indeed a problem, as others have mentioned. However...

You can have almost-conventional firearms that don't impart equal and opposite momentum to the shooter and the projectile. These exist in the real world as recoilless weapons. The basic idea is that a countermass is ejected rearward at the same time that the projectile fires, negating most or all of the recoil. The most straightforward way I can imagine doing this for small arms is to essentially make each cartridge a very small rocket with its own propellant. The propellant -- and not the shooter -- is the reaction mass used to set the projectile in motion.

An ill-timed nudge can be devastating

The projectiles in question don't need to carry much momentum to cause an unprepared (e.g. floating) target to tumble wildly. A beanbag fired at much lower velocities than those used in modern crowd control weapons would easily do the trick. (Watch how effortlessly this astronaut can propel her whole body down a tunnel in the ISS.) The target would only need to tumble a little bit to completely spoil their aim, and hence, ability to return fire. That target would effectively be out of the fight until they reach a bulkhead, stop their tumble, re-orient themselves, reacquire a braced position, and re-engage.

Without covering fire, they're a sitting duck for attackers to dart into melee range for a killing/disabling attack with a close-combat weapon. Observe how helpless this astronaut is when he can't reach a bulkhead. Imagine how well he would be able to defend against something as simple as a knife if he was tumbling.

A fighter that can't move can't fight

Even braced targets aren't immune to slow-moving squishy bullets. Effectively engaging in a firefight requires some freedom of movement. Bracing against a bulkhead may keep a fighter from being thrown into a tumble, but that also means she has to stay in place, braced against a bulkhead. Unless she can maneuver to keep the pirates from reaching the cargo hold/bridge/engineering/whatever, there's little she can do to actually deter the pirates. To maneuver, a combatant has to forfeit their braced position, making them vulnerable to beanbag bullets.

The exception to this is choke points, where the defenders can simply hold position and keep invaders from breaching, which is no different than choke points on land.

Asymmetry forces action

The home-field advantage -- combatants on a ship being boarded in a universe with pirates likely have some kind of remote-operated high-powered weapons mounted internally to protect vital areas from boarders. Being remote-operated, harming friendly defenders isn't a concern, so overwhelming force can be used... ricochet and debris be damned.

That means the pirates can't simply go toe-to-toe with the ship's primary defenses without being turned into Swiss cheese. They must first disable automated defenses, requiring them to take initiative. What boarders have going in their favor is that there's a lot of ways to disable a remotely-operated system without physically approaching it. That allows them to take initiative in an unpredictable way.

Since the boarders' movements through the ship will be difficult to predict, the defenders must be able to react and move to counter the boarders' actions, meaning they can't just hunker down and wait out the boarders.

Combat doesn't require lethality

The whole point of combat is to degrade an opponent's ability and/or willingness to resist to the point where they can no longer do so effectively... ideally as quickly and decisively as possible. Throughout most of human history, that simply meant "deal physical trauma as quickly as possible."

Combine the points above, and you have effective means to use small-arms projectile weapons in space combat without needing magnetic boots, bullet-proof hulls, or vacuum suits. Moreover, neither side can simply hunker down and out-wait the other; both sides are required to be dynamic and respond to changing circumstances, even if all small-arms weapons are very low-powered.

As an added bonus, scenarios like this would ensure that the victors of a battle would be likely to take a lot of prisoners, which opens up options to escalate the stakes of a fight as needed for the story. I'm not sure if being shot and bleeding to death is any worse than choking to death in a ship whose CO2 scrubber has been disabled by sadistic pirates...

Hull Breaches

sphennings is absolutely right: hull breaches are a much bigger concern than ricochet. With that said, if metal-piercing projectiles are used, hull breaches during a firefight are practically inevitable, meaning loss of atmosphere is a problem. As Ryan_L mentions, a single hole is actually pretty tolerable.

The trouble is, a firefight is going to involve a lot of bullets that miss their target, and each is likely to punch its own hole into empty space. It won't take long for any ship to turn into an oversize cheese grater. Explosive decompression isn't an issue, but hemorrhaging air during the entire duration of a firefight means combatants will eventually be fighting in vacuum. Moreover, all a pirate has to do is punch a decent-sized hole in the hull and wait. Similarly, defenders can just hole up in a sealed compartment, dump atmosphere from the rest of the ship and wait.

For any side: fighting without wearing a suit that can protect against vacuum would be utterly suicidal.

With that said, having a suit with a hole in it is only slightly better than having a hole in the hull, so any suit intended for use in vacuum should be rugged enough to not accidentally tear open under any reasonable circumstance, including stray debris flying around. This applies to any vacuum suit, not just those intended for combat, which likely have armor that would further protect from debris.

In other words, unless a combatant is literally trying to die, they'll be wearing a suit that will protect from small-arms ricochets and spalling.


Low velocity projectiles. Because everything is valuable in space.

Your pirates fire massive, slow moving projectiles. I here assert they are rubber ducks full of gold shot (gold being cheap in space, and it matches the duck). These gold ducks pack a wallop and will bounce (and quack) off of surfaces but have no penetrating power.

The idea is to incapacitate persons offering resistance. Just as the ship is valuable so are the people. Space is big and everything is scarce. If the brave folks offering a fight get a concussion or a few ribs broken by a gold duck they will be more tractable.

Also it is easier to surrender if you know your captors are going to give you a hat with their logo and put you right back to work, doing your old job for a different boss. Your captain might make more of a stink because they are going to evict him from his swanky quarters, but he washed space dishes for several years and he remembers how.


This is a solved problem actually. The answer is frangible bullets. These are softer or more brittle than the skin of the average spacecraft, so misses don't puncture the ship. But they're sturdy and heavy enough to still pierce flesh. US Air Marshals use bullets consisting of powdered copper in a nylon shell. If they hit a bad guy, he'll still be injured/killed because the projectile weighs about the same as a normal bullet. But they don't need to worry about overpenetration because the nylon shell will break on contact with the target, and powdered copper will basically never make it all the way through someone. They don't need to worry about a miss puncturing the skin of the aircraft because, once again, the nylon shell will break on impact and leave just a puff of copper dust. There's no reason your space pirates couldn't do the same thing.

Further, even if they do puncture the skin of the spacecraft, that's unlikely to be an instant death sentence for everyone on-board. The International Space Station had a leak in 2018 that was found to be a 2mm hole that had been accidentally drilled through the skin of the Soyuz module. It didn't suck everyone through it or cause explosive decompression, it was just a leak. A bullet hole isn't much larger.


Energy weapons like electritcity throwers, Cyro cannons, flame throwers, fragmenting rounds, lasers, sound waves, microwaves etc etc.

Basically if you want specialist boarding teams then that's the way I'm going. The cool thing is those weapons are damn nasty to the poor bastards on the receiving end of them.


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