Jet & Cones (Flamethrowers, Fire Extinguishers etc.) in Vacuum and/or Zero-G?

[vicky_molokh]

Greetings, all!

Our party is preparing to get into a spaceship wreck. Microgravity/Zero-G/freefall ensues, and there is no atmosphere in some of the compartments. But we're likely to have a need for at least one liquid/aerosol-spraying weapon - possibilities include a fire extinguisher (UT83, HT29), a spray can/tank (UT134), and/or a vortex ring projector. Yes, I know a VRP is neither a Jet nor a Cone, but title string length is limited.

So, what I'm interested in:
What are the effects of zero-G, vacuum, and both, on these different Liquid Projector class weapons. I'm guessing that a significant reason for the extremely short range of fire extinguishers is the gravity-caused falling of the projectile substance. OTOH, it seems likely that for spray-cans and vortex ring projectors, atmospheric interaction is a significant factor. And it's not clear whether a default vortex ring will keep flying indefinitely in vacuum without rotating, or change into a Cone under the pushing-outside effect of the gas. Or whether a VRP can have a vacuum-mode that does not form a ring, but rather launches the substance in a more vacuum-appropriate way, say, comparable to a flamethrower jet, a spitting cobra-style burst or whatever.

Thanks in advance!

[Agemegos]

I would imagine that the main limitation on the range of fire extinguishers, flame-throwers etc. would be the slowing of their streams by air resistance. The stuff they spew is going to continue indefinitely in vacuum, but in free-fall without vacuum they'd act much as normal. But there is a likelihood of the cone or stream expanding into vacuum faster than into air: you might get a wider cone.

I don't think vortex ring projectors will work at all in vacuum, producing only a puff of propellant and not of the smoke-ring effect.

As for flame throwers, without a special composition that includes an oxidiser with the fuel they won't burn in vacuum.

As they expel large volumes of ejecta at low speeds compared with firearms, such things as fire extinguishers may produce significant problems with recoil in free fall (i.e. they will act as rockets).

If you have high-performance individual rockets for EVA, consider using those as improvised weapons.

[vicky_molokh]

Originally Posted by Agemegos

I would imagine that the main limitation on the range of fire extinguishers, flame-throwers etc. would be the slowing of their streams by air resistance. The stuff they spew is going to continue indefinitely in vacuum, but in free-fall without vacuum they'd act much as normal. But there is a likelihood of the cone or stream expanding into vacuum faster than into air: you might get a wider cone.

Any way to estimate whether/when a Jet would turn into a Cone, or how much wider a Cone would become?

Originally Posted by Agemegos

I don't think vortex ring projectors will work at all in vacuum, producing only a puff of propellant and not of the smoke-ring effect.

A puff will do, as long as it still flies in a reasonably predictable manner for a reasonable distance (even 10 yards is good, though up to 40 would be even better). The question is, would it.

Originally Posted by Agemegos

As for flame throwers, without a special composition that includes an oxidiser with the fuel they won't burn in vacuum.

Of course. But I'm more interested in 'ballistic' properties: Jets of rather great lengths are what interests me in flamethrowers, and how this behaviour would change in freefall, or freefall with vacuum. (I'm pretty sure TL10 flamers with oxidisers would be almost the default, but we're unlikely to pick a flamer . . . for now.)

Originally Posted by Agemegos

As they expel large volumes of ejecta at low speeds compared with firearms, such things as fire extinguishers may produce significant problems with recoil in free fall (i.e. they will act as rockets).

Indeed. Which is why mag/sticky boots are the default assumption for my character ever since first flight. And . . .

Originally Posted by Agemegos

If you have high-performance individual rockets for EVA, consider using those as improvised weapons.

Compressed-gas thrusters, most likely the hand model. Indoor mobility is unlikely to benefit from carrying around a broomstick-rocket, but having some way to reach a wall/floor/ceiling in case of loss of contact seems like something worthwhile to me.

[Agemegos]

Originally Posted by vicky_molokh

Any way to estimate whether/when a Jet would turn into a Cone, or how much wider a Cone would become?

I remember estimating the speed with which a gas would eland into a vacuum as a function of its pressure and temperature when I was a freshman. But that was 1982, and I've forgotten. I'd compare the speed of expansion with the speed of projection to estimate the width of the cone.

A puff will do, as long as it still flies in a reasonably predictable manner for a reasonable distance (even 10 yards is good, though up to 40 would be even better). The question is, would it.

I don't know, but I doubt it.

Compressed-gas thrusters, most likely the hand model. Indoor mobility is unlikely to benefit from carrying around a broomstick-rocket, but having some way to reach a wall/floor/ceiling in case of loss of contact seems like something worthwhile to me.

I was thinking that there might be something in a locker for outdoor use that might be pressed into service in an emergency.

[johndallman]

Originally Posted by vicky_molokh

A puff will do, as long as it still flies in a reasonably predictable manner for a reasonable distance (even 10 yards is good, though up to 40 would be even better). The question is, would it.

No. Without a surrounding atmosphere, the vortex-ring confinement effect doesn't work. The gas molecules just fly off in random directions at their thermal velocities, which are much higher than their shared velocity component from the projector. I don't think you'll get anything noticeable as close as one yard. What were you planning to fire in vortex rings?

[vicky_molokh]

Originally Posted by johndallman

No. Without a surrounding atmosphere, the vortex-ring confinement effect doesn't work. The gas molecules just fly off in random directions at their thermal velocities, which are much higher than their shared velocity component from the projector. I don't think you'll get anything noticeable as close as one yard. What were you planning to fire in vortex rings?

Any suitable aerosolised oily substance with a distinct colouring. The purpose is to counter enemy Obscure (cloud of prism smoke, metal particles and some other stuff that fraks up most electromagnetic sensors one way or another), and potentially paint the enemy to prevent uses of Chameleon.

[Agemegos]

Originally Posted by johndallman

No. Without a surrounding atmosphere, the vortex-ring confinement effect doesn't work. The gas molecules just fly off in random directions at their thermal velocities, which are much higher than their shared velocity component from the projector.

That's about what I thought, too.

[Genesis]

Originally Posted by vicky_molokh

Any way to estimate whether/when a Jet would turn into a Cone, or how much wider a Cone would become?

This is going to vary wildly with the specifics of the weapon. A classical flamethrower, which works with a relatively non-volatile fuel, won't turn into a cone at all (although without gravity to wick away smoke etc. any use of it will be seriously obscuring, doubly so because the expanding gas cloud of consumed fuel will expand to fill the entire space). The spread of a cone will depend on how fast the individual particles are moving and how much they interact with each other (i.e. a fire extinguisher-like cone of small particles will expand because of the gasses used to eject them; a dragon's breath-like cone might not, if it works like a liquid flamethrower, or might, if it works like a blowtorch). My guess is that, for things that'll spread (gasses, mostly, volatile liquids as they flash-boil and evaporate), they'll spread a lot, like probably a catastrophic amount for whoever's wielding them.

A puff will do, as long as it still flies in a reasonably predictable manner for a reasonable distance (even 10 yards is good, though up to 40 would be even better). The question is, would it.

As other have said, no it won't - the vortex ring effect is predicated on an atmosphere. It'll work in micro-g, though, no problem.

Of course. But I'm more interested in 'ballistic' properties: Jets of rather great lengths are what interests me in flamethrowers, and how this behaviour would change in freefall, or freefall with vacuum. (I'm pretty sure TL10 flamers with oxidisers would be almost the default, but we're unlikely to pick a flamer . . . for now.)

In freefall the jet would continue in a straight line (according to inertia - don't forget the Coriolis effect in small stations that'll make it look like it curves) until the fuel is consumed or it hits something. Of course, for a flame thrower, you're going to generate large clouds of exhaust gases and smoke along the whole length of the thing (worse as it goes out and the speed of the stream decreases) that won't dissipate the way they would on a planet (no gravity to help hot clouds rise). You can see looking at videos of flamethrowers that there are two effects on the stream at larger distances: one is the arc of gravity - this will not happen in freefall, obviously. The other is the slowing of the stream with air resistance and stream spread. This will certainly happen in freefall, perhaps even to a greater extent than on a planet - surface tension effects are relatively more pronounced without gravity around to obscure them. But the stream will maintain some momentum... say that after the normal range the next turn the fuel continues in a straight line for half the distance, and does so every turn thereafter until it hits something. That's not scientific, of course.

[vicky_molokh]

Originally Posted by Genesis

This is going to vary wildly with the specifics of the weapon. A classical flamethrower, which works with a relatively non-volatile fuel, won't turn into a cone at all (although without gravity to wick away smoke etc. any use of it will be seriously obscuring, doubly so because the expanding gas cloud of consumed fuel will expand to fill the entire space). The spread of a cone will depend on how fast the individual particles are moving and how much they interact with each other (i.e. a fire extinguisher-like cone of small particles will expand because of the gasses used to eject them; a dragon's breath-like cone might not, if it works like a liquid flamethrower, or might, if it works like a blowtorch). My guess is that, for things that'll spread (gasses, mostly, volatile liquids as they flash-boil and evaporate), they'll spread a lot, like probably a catastrophic amount for whoever's wielding them.



As other have said, no it won't - the vortex ring effect is predicated on an atmosphere. It'll work in micro-g, though, no problem.



In freefall the jet would continue in a straight line (according to inertia - don't forget the Coriolis effect in small stations that'll make it look like it curves) until the fuel is consumed or it hits something. Of course, for a flame thrower, you're going to generate large clouds of exhaust gases and smoke along the whole length of the thing (worse as it goes out and the speed of the stream decreases) that won't dissipate the way they would on a planet (no gravity to help hot clouds rise). You can see looking at videos of flamethrowers that there are two effects on the stream at larger distances: one is the arc of gravity - this will not happen in freefall, obviously. The other is the slowing of the stream with air resistance and stream spread. This will certainly happen in freefall, perhaps even to a greater extent than on a planet - surface tension effects are relatively more pronounced without gravity around to obscure them. But the stream will maintain some momentum... say that after the normal range the next turn the fuel continues in a straight line for half the distance, and does so every turn thereafter until it hits something. That's not scientific, of course.

Hmm. All that seems to indicate that our best bet is to use non-volatile liquids spread in jets (e.g. from a Spray Can, UT134), or cones (similar to extinguishers on HT29).

[johndallman]

Originally Posted by vicky_molokh

Hmm. All that seems to indicate that our best bet is to use non-volatile liquids spread in jets (e.g. from a Spray Can, UT134), or cones (similar to extinguishers on HT29).

Yup, although "non-volatile" is a different matter in vacuum. I suspect anything you might practically use will boil away within a second or two; having it well-chilled will slow this slightly.