Pretty self-explanatory. Could a spaceship use a "ClF3 Mortar" to fire copper shells at enemy vessels? At first glance, this seems like a good weapon: it can burn even in space and can set fire to metals, and even glass and normally flame-retardant substances. Best of all, it cannot be put out by venting atmos, as the only way to put out a ClF3 fire is by flooding the area with nitrogen or noble gases, a nearly impossible proposition in space. Thoughts?

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    $\begingroup$ Have you heard the joke about the universal solvent? $\endgroup$
    – nzaman
    Jan 29, 2019 at 15:33
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    $\begingroup$ Exactly that. :) $\endgroup$
    – nzaman
    Jan 29, 2019 at 15:36
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    $\begingroup$ As user535733 said in a comment on my answer to a previous question - "The power of an explosive in military use is secondary. The primary consideration is always reliability... We don't lack powerful explosives." $\endgroup$
    – Rob Watts
    Jan 29, 2019 at 17:10
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    $\begingroup$ Are you talking about realistic space combat, or the kind of space combat we see in movies? In movies, fighters are orders of magnitude too close and far too slow. In realistic space combat, objects are enormously far away (requiring guidance, not mortars), and are traveling so enormously fast that the kinetic energy is all you need to make a kill. $\endgroup$
    – Cort Ammon
    Jan 29, 2019 at 18:38
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    $\begingroup$ Why do you thinking venting the atmosphere won't stop it? CIF3 is its own oxidizer and so doesn't rely on the atmosphere to burn in that sense, but venting the atmosphere will almost certainly remove all of the CIF3, which is gaseous under normal conditions and would be vented along with the atmosphere. $\endgroup$ Jan 29, 2019 at 20:22

7 Answers 7


No no no no no no no no no. Bad idea.

Chlorine trifluoride is one of the most horrifying substances on Earth. Sure, it can kill people and destroy equipment. But it can also kill the people trying to use it as a weapon. It's difficult to contain and nearly impossible to fight if it starts a fire, and produces extremely toxic byproducts when it reacts with other things. The smallest error in handling it could quite easily kill everyone nearby.

Now, sure, you can handle chlorine trifluoride safely . . . but in a lab, where you have plenty of time to check and double-check and triple-check that things are being done right. You can afford to go slowly. The same isn't true in a war zone, where speed is of the essence. You can either handle the thing safely and get blown up when you can't use it in time, or you can rush to use it and get set on fire when it spills.

Let's look at some of the worst-case scenarios for using this thing in space:

  • There's a small leak in a storage unit, and chlorine trifluoride reaches a nearby surface, immediately starting a toxic reaction that will kill many people on the ship because they're trapped in space and have nowhere to hide.
  • The fluoride coating on the storage chamber or in the weapon being used to launch it develops an imperfection, and the substance chews through and destroys the equipment.
  • The spaceship gets hit by something, causing a breach that releases chlorine trifluoride and unleashes hell. Even a small piece of space debris could cause problems if it hits the weapon in the right place. Also, there are people around you trying to make your spaceship explodes. Even an indirect hit in the right spot could be . . . bad.

The Nazis tried to see if it could be weaponized in the years leading to World War II. They did produce it in non-negligible amounts, but it became clear that using it as a weapon would be a terrible idea in much the same way that mustard gas in World War I was a bad idea: It can turn on the soldiers attempting to deploy it.

The thing is not simply worth the risk.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Jan 31, 2019 at 10:52
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    $\begingroup$ In general, "it was too crazy even for the Nazis" is an instant disqualifier. $\endgroup$ Jan 31, 2019 at 21:12
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    $\begingroup$ Or it's one hell of a plot device! $\endgroup$
    – Alex H.
    Feb 1, 2019 at 23:07

Chlorine Trifluoride as a Space Weapon?

Not really. Indirectly useful? Yes, for disinformation.

  • Convince the enemy that you've found a way to effectively weaponise it. Contrive for them to "find" semi-destroyed plans for a weapon prototype in a way that they can't help but believe is real. (A courier ship on a desperate run carrying "plans" fights a desperate battle to protect them, not surrendering, finaly self destructing in a desperate sacrifice yada, yada etc. only a scrap of plan/data left)

  • On making them fall for it, they will gather their top chemists, materials scientists, top engineers and technicians in on place with what is the most uncontrollable, uncontainable, volatile, corrosive, poisonous substance a deranged chemist ever came up with.

Watch for the fireworks. Rejoice, in your enemy's gullibility and that you just cut the head off their science division barely getting your own hands dusty.

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    $\begingroup$ This is an answer the God Emperor approves of. $\endgroup$ Jan 29, 2019 at 16:05
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    $\begingroup$ It's a ruse to get them to fill tanks with "nitrogen or noble gases" and bring them into space for us to take away, by threatening them with the big dumb rocks we normally throw at each other. $\endgroup$
    – Mazura
    Jan 29, 2019 at 16:42
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    $\begingroup$ Charles Stross did a thing like that. $\endgroup$
    – jdunlop
    Jan 29, 2019 at 21:37
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    $\begingroup$ @ozone - it's false. Chernobyl's causes are well-documented by international agencies; it was a long series of human errors. Stross is good at postulating alternate causes that sound potentially plausible if you accept a ridiculous starting point. $\endgroup$
    – jdunlop
    Jan 31, 2019 at 18:50
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    $\begingroup$ @jdunlop Thanks. Pretty cool article either way. $\endgroup$
    – ozone
    Feb 1, 2019 at 18:47

Your question can be generalized as "oxidizer weapon". Oxygen or ozone shells would do same thing, although not as intense. You write that

it cannot be put out by venting atmos

but actually it could. What you're trying to do is to create CIF3 atmosphere to burn enemies, but venting it to space would vent it like any other atmosphere. If you could manage to inject an airtight enemy with it, it would work, but otherwise all you get is some minor etching in the split-second before space vacuum "sucks" all your CIF3.


As others have pointed out, there are some problems with this idea. One that I want to point out is that for this weapon to be effective you must first hit an enemy with the shell.

This will be accomplished by mounting your copper vessel in a magnetically accelerated slug or self-propelled missile. Connecting with the enemy ship is the hardest part. Engagements are likely to take place at pretty extreme ranges, and ships will probably have decent avoidance maneuvers.

Once you hit the enemy, the shell must be strong enough to penetrate the hull and deliver the payload. When you compare the chemical energy stored in your ClFl3 to the kinetic energy required to accomplish the above, we don't really add much.

Yes, a ClFL3 fire in a critical area would be devastating on a ship. But so would the exact same impact from a traditional chemical munition, or even just an inert kinetic impactor.

If your shell is too weak to get through the hull, it would splash against the armor, react with a small amount of the hull material, be explosively ejected by its own reactive byproducts, and disperse into the vacuum of space with minor damage done.

It doesn't look much better if your shell breaches the hull in a shallow manner either. The hull breach will cause explosive decompression, venting the atmosphere AND your ClFl3 before it can react with much.

Well made ships will have self sealing compartments to deal with hull breaches, so you might do some damage to the area directly adjacent to the impact site.

The shell would have to detonate in the middle of the ship for maximum effect.

A design to accomplish this could have an armor penetrating exterior, then detonate and scatter a bunch of smaller sealed copper spheres like a shotgun blast that would ideally breach the inner walls and then combust.

Overall, there is little to gain from conventional munitions with this approach.

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    $\begingroup$ This suggests that the stuff might be better used by a saboteur or terrorist. $\endgroup$
    – Mark Wood
    Jan 31, 2019 at 17:41
  • $\begingroup$ I mean, maybe? The problem with that idea is how dangerous this substance is to create and work with. Again, more conventional munitions would probably be sufficient to cripple a ship from the inside, and your ship will probably have some onboard already. $\endgroup$
    – abestrange
    Jan 31, 2019 at 18:00

ClF3 is surely a very destructive thing. Storing it aboard your spaceship is too risky, sure, as other answers have noted.

The space, however, is made of space, lots of it :) So typically, there will be quite a bunch of space between you and your enemy, be it spaceship combat or orbital bombardment. If some ClF3 happens to destroy your enemy, most likely it won't affect you at the same time, since it's all far away, and there's not enough of it to cover the distance. You just have to stay safe from it before and while you apply it.

So the obvious solution is to drop a machine producing ClF3 upon your enemy. Even the nukes do their job via a nuclear reaction, but that reaction isn't run at our military bases, ships or planes; a projectile starting that reaction when it arrives is used as a weapon instead.

Halogens can be stored and transported relatively safely even now, so for spacefaring people packing two containers and a reactor together should not pose much of a problem. Of course, the enemy can try to destroy the bomb before the reaction has even started, just like missile defense this days tries to stop ICBMs. And countermeasures similar to those of ICBMs can be built into ClF3 factory-bomb (decoys, antiradar measures, etc.)

The real question is whether it's all worth using. What ClF3 can do to an enemy spaceship that a good old atomic bomb can't do? Surely the nuclear reaction has more energy than any sort of oxidizing, no matter how intense or quick. So it apriori will do more damage.

But things get even worse for our nasty chemical, if one thinks more. Space requires a lot of energy, so if it's at larger scale than us earthlings going around the Solar system, a spaceship has access to some energy source probably more powerful than nuclear or thermonuclear. What chance has any oxidizer to compete with the annihilation power scale?

So space warfare will resort to ClF3 only on some specific circumstances:

  • Nuclear and more powerful stuff is effectively countered by the enemy. Shields, atomic suppression, or anything else in the same vein.
  • Or it's just banned by acting rules of engagement.
  • Or it's used intentionally as a nasty disgusting weapon that people normally don't use to shock the enemy.
  • Or the nuclear materials are unavailable or prohibitively expensive for some reason, so chemical weapons become a necessity, and the strongest oxidizer all can come into play.
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    $\begingroup$ +1 for pointing out that chemical reactions are on the wrong energy scale for (most) space-age weapons. To put it another way; CIF3 is sword-chucks, the deadliest melee weapon (it usually kills the wielder too!). But using sword-chucks during WW2 won't do anything useful. $\endgroup$
    – Yakk
    Jan 29, 2019 at 19:12
  • $\begingroup$ @Yakk sword chucks, yo $\endgroup$ Jan 30, 2019 at 2:29
  • $\begingroup$ Not sure about sword-chucks, but sword fights actually took place during WW2. $\endgroup$ Jan 30, 2019 at 15:05

The only thing even less practical is to whip up a batch of FOOF and attempt to hit your enemy with it before your own ship is consumed. Maybe a kamikaze run?

Seriously, with 1960 era technology scientists were contemplating compact nuclear devices which would project star hot plasma at a small fraction of the speed of light (Casaba Howitzer). We now know how to make electromagnetic rail guns, reliable laser weapons, "Third generation" nuclear weapons (imagine a HEAT warhead designed to crack open a mountain), non-nuclear EMP devices...

The greatest danger I can think of for my ships crew is they will be distracted by their hysterical laughter once they realize what you shot at them. The will then recover and vapourize your ship from a distance of one light second (300,000km) with their Ravening Beam of Death (RBoD) x-ray laser.


This would make for a fantastic story...

As I sit here pondering the issue, I wonder about, "what if you have two or three chemicals that, when mixed, produce ClF3? Put those in a warhead" and "what would happen if you used this stuff in a mine field, assuming some unobtainium even it couldn't react with?"

HDE 226868 is absolutely correct, it would be the height of insanity to use this stuff in space combat — but that doesn't mean it wouldn't make one whale of a good story.

  • Imagine flying through space and inconveniently running through a cloud of this stuff. Imagine doing that from some ancient battle in a "million-to-one chances happen all the time" Star-Trek-ish sort of way. The stuff would rip the hull off your ship.

  • Imagine a missile that happened to impact with a ship using water as its primary radiation shielding. Flash of fireworks, ship shell floating off into space, crew subjected to the horrors of radiation.

  • Imagine the innumerable failsafes, the unending training, octuple-redundant computer monitoring, and still some idiot (usually the new guy) slips on his own spit and happens to knock off the adamantium valve in one of those "Dang! I dropped the wrench and blew up the missile!" moments.

Granted, your story had better be a horror story, and there are obviously great reasons in reality to never ever ever touch this stuff under any conditions lest the Olympian gods return and invest you with some never-to-be-completed task...

But the stuff would make for a great story. Really, how often have we heard the "but mutagenic weapons have been banned by all civilized species!" trope? This stuff was designed from the foundation of the universe to fulfill that trope!

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    $\begingroup$ This assumes CLF3 is a spontaneous product of some reaction. It is not. Here is a chemistry tip. The most spontaneously reactive species are usually not spontaneously produced themselves. The abomination that is ClF3 is disgustingly reactive, and even the products if you let it roam wild are acutely toxic and reactive (less reactive than ClF3 but still). There is nothing that spontaneously produces it. You have to coax it into existence, and even then it threatens to non-exist and you alongside it. $\endgroup$ Jan 30, 2019 at 9:05
  • $\begingroup$ @StianYttervik, while true that a portion of my answer assumes the simple mixing of chemicals, it doesn't change the fact that the creation of ClF3 is nothing more than a process. We're in space having a battle, one can logically assume that the automation of that process on a small scale inside of a warhead is plausible - possibly not practical, but plausible. Frankly, the more difficult it is (so long as some future tech can automate the process) the more interesting it would be in a book. $\endgroup$
    – JBH
    Jan 30, 2019 at 17:44
  • $\begingroup$ @JBH highly reactive and highly explosive substances are useful as weapons because they essentially contain large, concentrated amount of available chemical energy that can be delivered upon the target. Making those substances requires investing that energy, and doing that "on site" is counterproductive; if your power supply has less energy density than CIF3, then you can get more CIF3 there by delivering CIF3 instead of energy for making CIF3; if your power supply has more energy density than CIF3, then it itself is a better weapon than CIF3, just release the power directly in some way. $\endgroup$
    – Peteris
    Jan 31, 2019 at 19:26
  • $\begingroup$ @Peteris, Your explanation translates to, "the process of making a nuclear bomb is a better bomb than a nuclear bomb." I do not dispute your basic assertion because the conclusion is also true: the delivery of the manufacturing process in the context of a weapon is almost always more complex than simply delivering the weapon - which is why we drop nuclear bombs rather than the manufacturing processes that build the bombs. But we're creating fiction, not documentaries, and the idea of miniaturizing the process using future tech such that we get exactly what you're explaining is wonderful. $\endgroup$
    – JBH
    Jan 31, 2019 at 19:48

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