I know from here that a flame thrower can operate in deep space if specially built. However, I want to know if using a flamethrower on a spaceship in space could have any tactical benefits. Could a flamethrower be used to destroy or blind enemy sensors from several kilometers away, or would it burn out? Would it be possible to build a flamethrower that can reach targets several kilometers away in space?
Remember that the purpose of a flamethrower is to set flammable targets on fire like wood structures and humans and to consume oxygen from enclosed spaces. It is safe to assume that spaceships will not be made out of flammable materials. Ships are sealed so that they do not lose oxygen to space, so unless the flamethrower can penetrate the hull it will not harm the air inside the ship. There are also far more effective methods to blind enemy sensors than generating a lot of heat and IR. Space ships already are going to be able to filter out far hotter things from their sensors like near by stars.
Distance and Velocity
For a flame thrower to travel one kilometer it would need to ignite at the end of the stream on impact otherwise it will burn its fuel off before it got to the target.
Flamethrowers also run into an issue that the fluid is not going to be moving that fast compared to other weapons so enemies will easily see it coming and avoid it. You can switch it out for an incendiary missile, which will get the payload to its target faster, but it will cease to be a flamethrower at that point.
Armor and Shields
Space ships are going to be designed to handle far worse than what a flamethrower can dish out. Flamethrowers are a chemical based weapon and so they generate energy through chemical reaction. However, there are a large number of weapons out there that can generate far more destructive forms of energy, and as such space ship defenses will be designed to handle those types of things. So when the flamethrower hits the shields or armor at the worst it will likely only damage the paint job.
Why would you do this? Usually space weapons are high energy high velocity.
There's benefit to utterly unexpected tactics. Flamethrower won't work for practical reasons, but how about some super caustic thermite goo?
"Sir, incoming" "Missile?" "Nope, too slow, no evidence of a guidance system" "Impact danger?" "Low mass and velocity, no danger of hull breeach" "Hold course, ready main missile batteries, energy weapons and rail guns." "Ready... wait, hull sensors in the area of impact are starting to go down" "Damage control teams to affected decks. What is it?" "It's goo, wait, now it's on fire, hull breech warning on decks three and seven, also four. Now five and six." "Fire control teams, seal all decks prepare for depressurization"
Bam. Goo wins the day.
A flamethrower is, fundamentally, a device that ejects burning-hot stuff at a moderate-to-fast speed.
A rocket is a device that ejects stuff at very fast speeds, and the stuff it ejects tends to be burning-hot (since that's a very effective way to make fast-moving exhaust).
If for some reason a spaceship builder decided to put a flamethrower on the outside of their ship, especially if it needs a range of several kilometers, it seems likely that it would be based on a backwards-facing rocket more than a traditional earthbound flamethrower. What you'd be looking at there would be weaponized exhaust - along with some (possibly rather significant) acceleration away from the target.
What you're essentially looking for is something that's fuel and oxidizer. White Phosporous's probably the good stuff. Add an oxidiser since space dosen't typically have an atmosphere, and something thick and sticky to carry it all and stick to surfaces, since there's no gravity in space. Maybe encapsulate the two chemicals so they don't react prematurely in heat-decomposing "cells". Since its space, lauching it as a stream makes no sense. Instead have them in canisters with an igniter that kickstarts the combustion. Launch them have them hit and splash on a target - vaguely like a HESH round then sets the fuel, which is stuck to the target on fire
Since space craft have limited capacity to dump out heat, this might actually end up being pretty nasty. It would be a complicated/rube goldbergian weapon though
You could also use them as decoys or flares as needed. However, I do suspect something like this wouldn't be as effective in most cases as big, dumb, fast projectiles, except against say a space station or other stationary target.
You could use a flamethrower inside as spaceship to devastating effect if a flamethrower is specifically what you want. However, if you want to attach a flamethrower to a spaceship that would not be the most effective use of a flamethrower or a spaceship. If you absolutely need to use a flamethrower in space consider drones. Drones can reach high velocities and hit enemy ships super far away. Then you might get some practical use. Particle cannons, missiles, and railguns are still probably more effective, though... I hope that was helpful!