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Spudguns in space

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: D_Hall » Sat Nov 21, 2009 6:44 pm

Brian the brain wrote:If I would create a vacume in a barrel, I would need to seal the muzzle.
Preferably with something like a plastic bag or aluminium foil burst disc.

Imagine the projectile going ( past) the SOS..
The projectile still has to break the seal...wouldn't that take it right back down below SOS?

Well, you certainly have to look at the tradeoff....

Does pulling a vacuum on the barrel add more energy to the projectile than punching through the diaphragm subtracts? If the answer is "no" then you won't want to go the vacuum route. If the answer is "yes" vacuum is viable. I suspect the answer is almost always "yes" and vacuum is viable. HOWEVER, that doesn't mean that viable is the same thing as cost/time effective. 99.9% of the time anything you're attempting to do by pulling a vacuum on the barrel could just as easily be done by using a slightly larger chamber (or higher pressures, or whatever).

Vacuum is the measure of last resort.

Put it this way: On the gun that I was using vacuum on, the gun used o-rings made of hardened steel... And those o-rings were being extruded. Translation? We were exceeding 120,000 psi. There really wasn't much more we could do... So we pulled vacuum.


And for what it's worth, in every "vacuum barrel" application I've ever seen, a couple layers of clear packaging tape is what's used on the muzzle.
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Re: Spudguns in space

Unread postAuthor: D_Hall » Sat Nov 21, 2009 6:52 pm

Ragnarok wrote:I didn't say they were firing continuously. I'm talking about use as if they were in combat - a few minutes of use of the firearm as would be expected under those conditions would be about enough to require the barrel to be replaced.

That sounds on the low side. I know when I was in Army Cadets that my webbing had the pouches to carry a dozen magazines (not that the bastards ever gave me that much ammo), so I'd expect that carrying ~500 rounds is normal enough for soldiers.

I still question the conclusion.

A continuous fire scenario is a worst case. Do you agree that you won't see significant convective cooling on something like a barrel in a mere 30 seconds? And yet, 30 seconds of continuous fire is something that guns are exposed to in proof testing all the time. HERE is a much more savage test (on admittedly a special gun). I just don't think you're going to see significant damage due to thermal effects with anything that resembles a normal rate of fire and a normal ammo loadout for the shooter.
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Re: Spudguns in space

Unread postAuthor: Ragnarok » Sat Nov 21, 2009 8:38 pm

D_Hall wrote:I still question the conclusion.

I admit it's rough calculations, but that was the rough conclusion made by calculating radiative cooling for an M-16.

As a rough rule, for a typical firearm, energy from the cartridge is split three ways in Projectile KE, Barrel heat and Energy left in the Muzzle blast, with other things being negligible. So that puts the M-16 generates around excess of 20 kW of barrel heat during firing.
Given the heat capacity of the barrel, that means a magazine will increase barrel temperature about 100 Kelvin (not sure if that's quite right, I'm trying to recall maths I did sometime back without the notes).

As it worked out, I think the radiative cooling (from the barrel only, disregarding other weapon structure) meant that the equivalent of 7 or 8 rounds a minute would hold the barrel at a temperature around 600 Kelvin - around about where you might expect creep to start in steel (which I considered the lower bound for barrel damage to be occurring)

Bringing that up to around a magazine a minute, and you're looking at 800-900 Kelvin equilibrium temperature. Hot enough for the barrel to be notably glowing red. It doesn't take much fire to sustain damaging temperatures in vacuum.

Obviously, you need to get up to those temperatures first, but if you fired a dozen magazines over 10 minutes? You'd lose your rifling, and your barrel would be nicely annealed. One replacement please.

Okay, it's only a hypothesis with some back of the envelope calculations, I admit - but I don't think it's a unreasonable conclusion to reach.
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 22, 2009 12:55 am

Ragnarok wrote:Also, as far as I understood, the TP-82 was largely for survival after landing back on earth. I can't see much reason for firing it in space...


Officially, but you never know :)

Now why hasn't anybody thought of the fact it can be extremely cold out there?


Good point!

As to the cooling issue, some heavy finning as seen on the Japanese type 92 would help:

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Re: Spudguns in space

Unread postAuthor: starman » Sun Nov 22, 2009 2:31 am

Ragnarok wrote:
Figure a soldier carries half a dozen 30 round clips.

That sounds on the low side. I know when I was in Army Cadets that my webbing had the pouches to carry a dozen magazines (not that the bastards ever gave me that much ammo), so I'd expect that carrying ~500 rounds is normal enough for soldiers.


A typical modern US Marine carries 180 rounds (6 mags x 30) of 5.56 NATO on a typical daily patrol. If serious fire fights are expected or something special is planned, they are told to "double up" or even "triple up" on their mags, going to 12 or 18 mags. They hate hearing the "double up" order because some serious poop is very possibly about to go down.
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Unread postAuthor: CpTn_lAw » Sun Nov 22, 2009 7:35 am

I think the first post was supposed to mention a steel QEV gun shooting in space. There is obviously no problem of continuous firing, let alone heat transfer, doubling-up magazines etc...
Obviously, this topic is going nowhere since I don't think any of us did research and experimenting in zero gravity and -273°C environments. Correct me if i'm wrong.
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Re: Spudguns in space

Unread postAuthor: Ragnarok » Sun Nov 22, 2009 10:41 am

starman wrote:A typical modern US Marine carries 180 rounds (6 mags x 30) of 5.56 NATO on a typical daily patrol. If serious fire fights are expected or something special is planned, they are told to "double up".

Then my point stands just fine. I'm not talking about a casual patrol, I'm talking about expected combat.

jackssmirkingrevenge wrote:As to the cooling issue, some heavy finning as seen on the Japanese type 92 would help

Actually, it would scarcely help at all. Radiant heat is projected off perpendicular to the surface - which would pretty much project the heat directly at the next fin.

Cooling things in space is actually quite a tricky problem. While radiative cooling is persistent, it's slow (a square metre at 300 K, cooling into space, can only lose about 450 watts - maximum).
Space is cold (about 3 Kelvin), but things do not cool fast out there.

One of the easiest solutions to cooling in a vacuum is boiling water - venting water into space will cause it to immediately boil off, taking heat with it (as it takes a lot of energy to boil water).

CpTn_lAw wrote:I think the first post was supposed to mention a steel QEV gun shooting in space.

The question was posed as the effects of a vacuum on performance. That answer is already given.

So now we get to have fun talking about the other problems space can cause.
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Re: Spudguns in space

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Unread postAuthor: CpTn_lAw » Sun Nov 22, 2009 1:15 pm

Space causes problem if we use Earth-made designs. Something that could be usefull in space would need to be thought for "space combat". Without inertial dampers, anything that launches solid matter is not practical.
Distances in space may require faster "projectiles", and since the only practical source of energy we can take is sunlight, i'd say we are in the electric weaponry department.
You could have a container filled with gas, possibly one with low ionisation energy. There could be a simple injection system, that would use the cold of space to cool little amounts of gas into solid rods. These could be inserted in a "barrel", and a high-energy microwave beam could be focused to the rear of the rod. Ionisation and plasmification of the gas would result in :
Light emision
drastic pressure increase
Heat
Consumption of energy.

The pressure generated by the quick temperature differential would propel the solid rod, much like an electro-thermal gun. Using a combination of self oxidizing gas would result in continuous burn (limited range) but acceleration gain even after the projectile is sent. I didn't calculate anything, so don't say "this is pure science fiction", it is. But, the principle could (with little faith ^^) work, and since this topic is pointless, my idea is not worse than any of those already stated.

So now we get to have fun talking about the other problems space can cause.


You're right. It is fun.
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Unread postAuthor: D_Hall » Sun Nov 22, 2009 1:48 pm

CpTn_lAw wrote:Distances in space may require faster "projectiles", and since the only practical source of energy we can take is sunlight, i'd say we are in the electric weaponry department.

Why do you say that? The modern soldier takes his energy with him stored in rifle cartridges manufactured thousands of miles away from the point of use. There's absolutely no reason why a gun (or whatever) in some space-based location couldn't use similar energy sources.
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Last edited by D_Hall on Sun Nov 22, 2009 2:21 pm, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 22, 2009 1:52 pm

The space weaponry idea I find most fascinating is the "rods from god" orbital bombardment concept, sheer kinetic energy.

A pair of satellites orbiting several hundred miles above the Earth would serve as a weapons system. One functions as the targeting and communications platform while the other carries numerous tungsten rods—up to 20 feet in length and a foot in diameter—that it can drop on targets with less than 15 minutes’ notice. When instructed from the ground, the targeting satellite commands its partner to drop one of its darts. The guided rods enter the atmosphere, protected by a thermal coating, traveling at 36,000 feet per second—comparable to the speed of a meteor. The result: complete devastation of the target, even if it’s buried deep underground.


:shock:
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Unread postAuthor: CpTn_lAw » Sun Nov 22, 2009 2:05 pm

Well, if you were to have a long trip into space, you would find it hard to find smokeless powder to fill the cartridges back. (If you find a way to take the cases back after they're spent) , but gas can be stored in much greater quantities, station could keep thousands of cube meters of those gases...

And i liked the idea of a plasma weapon in space ^^


Orbital strike is way fun JSR :D
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Unread postAuthor: D_Hall » Sun Nov 22, 2009 2:26 pm

jackssmirkingrevenge wrote:The space weaponry idea I find most fascinating is the "rods from god" orbital bombardment concept, sheer kinetic energy.

A pair of satellites orbiting several hundred miles above the Earth would serve as a weapons system. One functions as the targeting and communications platform while the other carries numerous tungsten rods—up to 20 feet in length and a foot in diameter—that it can drop on targets with less than 15 minutes’ notice. When instructed from the ground, the targeting satellite commands its partner to drop one of its darts. The guided rods enter the atmosphere, protected by a thermal coating, traveling at 36,000 feet per second—comparable to the speed of a meteor. The result: complete devastation of the target, even if it’s buried deep underground.


:shock:


:roll:

When you simply "drop" something from space.... It just hangs out in orbit right next to you. Want it to actually go somewhere? You'll need to put a rocket on it. Ironically, that rocket will need to comparible in size to what it would be if you were to simply fire an ICBM on a sub-orbital trajectory.

At that point... Just hit 'em with an ICBM.


edit: Not that I imagine you'll ever see ICBMs with kinetic warheads. There are significant political obsticles to that.
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Unread postAuthor: D_Hall » Sun Nov 22, 2009 2:31 pm

CpTn_lAw wrote:Well, if you were to have a long trip into space, you would find it hard to find smokeless powder to fill the cartridges back.

Given the costs of getting all your other stuff into orbit to begin with... So what? They're disposible. Single use.

Just like they are today (don't see too many Marines collecting brass during a firefight...).
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 22, 2009 3:09 pm

D_Hall wrote:When you simply "drop" something from space.... It just hangs out in orbit right next to you. Want it to actually go somewhere? You'll need to put a rocket on it. Ironically, that rocket will need to comparible in size to what it would be if you were to simply fire an ICBM on a sub-orbital trajectory.


It stands to reason that some sort of nudge would be required, otherwise:

"Unleash the kinetic rods! Let the orbital bombardment begin!"

"Rods released sir"

*cue shot of rod floating embarassingly across the screen*

Would it really need that much rocket power?

At that point... Just hit 'em with an ICBM.

Not that I imagine you'll ever see ICBMs with kinetic warheads. There are significant political obsticles to that.


Why's that, considering the point of the Navy's current railgun development is a pure kinetic weapon. The concept of "smart spears" - guided metal rods without explosive - dropped from high altitude bombers has also been floated around, at least by those at the Skunk Works:

We even dreamed up the creation of an energy bomb that used no explosive device. Flying at Mach 3 and eighty-five thousand feet, we'd drop a two-thousand weight of high-penetrating steel that would hit the ground with the force of a meteor -- about one million foot-pounds of energy and blast a hole 130 feet deep. The Air Force was interested, but fretted about the absence of a guidance system to assure pinpoint accuracy and resisted our suggestions to try to develop such a system. To the new Secretary of Defense, Robert McNamara, an energy bomb was futuristic drivel.


Fascinating stuff.

Given the costs of getting all your other stuff into orbit to begin with... So what? They're disposible. Single use.


The way things are going by the time space combat is a reality, the caseless/combustible case firearm would probably have become the norm, unless it was superseded by some other kinetic/energy weapon.

Ragnarok wrote:Actually, it would scarcely help at all. Radiant heat is projected off perpendicular to the surface - which would pretty much project the heat directly at the next fin.


How about one huge fin then, could also serve as a shield, with a visor cut out :)
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Unread postAuthor: jeepkahn » Sun Nov 22, 2009 3:35 pm

Agreeing with Dhall.... Vacuum assist gains are negligible on a high pressure or an SOS and faster gun(which I believe D's experiments with vac , were well beyond sos).

I think this quote: (The gas expands. It can't expand "backwards" as there's a pressure gradient. So it moves forward at an ever so slightly faster rate. This keeps happening in a continuous process until the flow is sonic. Mind you, getting this to happen may take significant pressure and tubes that are measured in many thousands of diameters in length (which generally means it only happens in a laboratorydemonstration), but the phenom of a subsonic flow going sonic has been demonstrated for generations.) Even though it wasn't intended in this thread, will explain why it makes a differance especial with light projectiles...

I just punched in the #'s in DD1 ggdt, launching a 10g projectile with 125psi and no vacuum gives a velocity of 1014fps, and the acceleration curve is 6300g's at 2" and it drops to 2100g's by 20", and with no other changes than evacuating the barrel, it gives a velocity of 1527fps and the acceleration curve is 7800g's at 2" and 3500g's at 20" and 2500g's at 40"...

I would also like to state that when I did a vacuum assist shot with a styrofoam ball one time, (I used a 2" to 4" bell reducer on the muzzle that had a small port drilled into the side for the vacuum pump, and a piece of 1/4" thick styrene greased and sucked to the muzzle) when the styro ball exited the muzzle (disentegrating the styrene sheet) the sound was deafening and the bell reducer exploded into about a million pieces from what I gather was the shockwave that propagated once the vacuum had been compromised by the ball exiting the barrel ....
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