Bullets in vacuum?

[Lowly Uhlan]

Well after 3 months of design work, my Star Hero game is allmost ready to go. I'm going for "hard" SF and have a question:

 

What would happen if a modern-day bullet was fired in vacuum? Would the absence of air stop the combustion needed to propel the bullet? I figured the collective intellect of this forum would be a good place to get an answer.

[Intrope]

Smokeless powder will burn in a vacuum (it provides it's own oxygen). So, a bullet should work fine in a vacuum.

 

However, other issues may come up. People firing bullets in zero g will fly off the other way, for instance. Shots at significant distances (one spacecraft to another) may require orbital computations to get right. Sights on long-range weapons will need to be recalibrated when switching from gravity to zero g (since the bullets won't arc anymore). Also, the temperature may become a factor--in naked sunlight, items can be heated up much higher than normal (which could cause rounds to detonate with too much force, rupturing the weapon or otherwise misfiring). Items in shadow can cool down to really low temperatures--I suspect that the powder might not work if it is cryogenically cold.

 

Of course, most of these problems might be accounted for by people who are planning on taking weapons into space; these problems are all issues with current era smokeless powders.

[Drakkenkin]

I was going to post on this subject with an absolute answer, but I don't know enough about all the different types of materials that could be used as a propellant. My answer was going to be "The gun would not fire do to the lack of oxygen for the chemical reaction that takes place at the time of the firing of the gun." ,but if smokeless gun powder creates its own oxygen then it may work. The only other reason it would not work is because of the extreme temp's in space (both cold and hot). If the material is to cold I don't think the chemical reaction would take place as it needs energy in the form of heat, and if the ammo got to hot it would 'detonate' in its ammo case or the barrel.

 

Intrope has already stated some of this, nevertheless here is some more. The barrel and the projectile of the weapon would expand when they got hot and contract when they got cold, enough to lower accuracy or cause the projectile to get caught in the barrel; causing the barrel to become damaged or explode.

 

You could say that the weapon have equipment to help it stay at a near constant temp'. It would take up quite a bit of power form the ship to combat the extreme temps. in space, but it's an easy solution.

 

There are new materials being created all the time with new proprieties. I know your trying to run a hard SiFi setting, but unless your setting is set with the current tech levels of earth, there will be changes in the future. Have someone in the future create a material that resists distortion in shape from heat/cold, and a projectile that is self contained (not dependent on its atmosphere). It would also make more scene to have the projectile fired by an electric charge instead using a hammer as in conventional weapons (some what like C4).

 

Drakkenkin

 

PS: Kristopher you caught me as I was MODing the letter.

[Kristopher]

Originally posted by Drakkenkin

The gun would not fire do to the lack of oxygen for the chemical reaction that takes place at the time of the firing of the gun.

 

Drakkenkin

 

As already noted, smokeless powder doesn't need external oxygen in order to burn. Note that the rounds are sealed.

[Guest zarglif69]

Originally posted by Kristopher

As already noted, smokeless powder doesn't need external oxygen in order to burn. Note that the rounds are sealed.

But not airtight.

[BoneDaddy]

A ceramic slug thrower with caseless rounds could work. There are obvious propellant issues that are possible with explosives. Given the natural properties of a gas (it will try to expand to uniform pressure throughout its container, even when that container is vacuum filled nothing), a tube of compressed nitrogen should work about as well as an explosive charge, especially in a near frictionless microgravity environment.

 

A .38 special? I doubt it, frankly. There are temperature concerns, and any gas inside the shell casing will try to push out the round. The rifling on the barrel will be an impediment rather than a boon in a vacuum, I think, in that they would allow the gases more opportunity to slip past the slug, without there being any gases on the other side of the slug for them to interact with. Additionally, with a semi you get shell casings bouncing around, littering up the battlefield (assuming quarters more confined than the inky blackness of space) which is a real hazard, especially if when are hot. Earth designed munition just seem dangerous for weightlessness.

[Dr.Device]

There have been lots of discussions about this in the usenet group rec.arts.sf.science. You might want to check some of those out in Google groups.

 

The above comments on smokeless powedered covered the firing issue, but two other issues you should consider are vacuum welding and sublimation of lubricants. Any normal lubricant is going to become worse than useless fairly quickly in vacuum as its volatiles evaporate, leaving the residue to gum up the workings of the gun. Without any lubrication, the gun's mechanisms would be subject to vacuum welding; the little bits of metal would become bonded together where they made contact.

 

These problems are not insurmountable, and would probably have been dealt with early in the history of space warfare (if there is any) in your campaign. The main reason to keep them in mind is that it is unlikely that the same gun would be ideal for both vacuum and atmospheric use.

[Guest zarglif69]

Originally posted by BoneDaddy

A ceramic slug thrower with caseless rounds could work. There are obvious propellant issues that are possible with explosives. Given the natural properties of a gas (it will try to expand to uniform pressure throughout its container, even when that container is vacuum filled nothing), a tube of compressed nitrogen should work about as well as an explosive charge, especially in a near frictionless microgravity environment.

 

A .38 special? I doubt it, frankly. There are temperature concerns, and any gas inside the shell casing will try to push out the round. The rifling on the barrel will be an impediment rather than a boon in a vacuum, I think, in that they would allow the gases more opportunity to slip past the slug, without there being any gases on the other side of the slug for them to interact with. Additionally, with a semi you get shell casings bouncing around, littering up the battlefield (assuming quarters more confined than the inky blackness of space) which is a real hazard, especially if when are hot. Earth designed munition just seem dangerous for weightlessness.

In the novel Protector, a Pak Protector caused a neutron star to quake by firing a bullet into it.

[Metaphysician]

Vacuum welding??

[Lowly Uhlan]

Thank you sirs!

 

In my game those "advancements" mentioned earlier have been made. I asked about a modern day bullet as a basis for where I was going to take ballistic tech..I had thought about normal bullets firing the firerer in the opposite direction, spent casings floating round, the effects of temperature.

 

So the player characters (packing some of the highest tech the Sol System has to offer) will be firing caseless ammo from recoiless weapons. Liquid nitrogen as a propellant? I like the sound of that. The lower tech forces will be using smokeless gunpowder fired from guns that have heat and cold resistant weapons (and ammo casings). Probably recoiless. If the players ask about recoil (which I doubt they will) I'll say "It's because of the gun's special design.":D

 

But hey, feel free to chime in further.

[Dr.Device]

Originally posted by Metaphysician

Vacuum welding??

In a vacuum, pieces of metal in physical contact with each other will tend to become physically bonded. I believe that the mechanism is migration of atoms between the two surfaces, but I'm not sure about that.

[travellerne]

Originally posted by Dr.Device

In a vacuum, pieces of metal in physical contact with each other will tend to become physically bonded. I believe that the mechanism is migration of atoms between the two surfaces, but I'm not sure about that.

 

Unless something has changed, the two surfaces must be the same metal. Otherwise, the different sized atoms just don't "fit" together.

 

K.

[AnotherSkip]

Graphite, Powdered.

ought to solve it all.

 

the lubricant is dry, does not bond with metals and is easily made, common and easily applied.

[Arthur]

Originally posted by Intrope

Smokeless powder will burn in a vacuum (it provides it's own oxygen). So, a bullet should work fine in a vacuum.

 

That's correct. More technically, smokeless powder is made with nitroglycerine: C3H5N3O9. Note the nine oxygen atoms. That's plenty to support combustion.

 

Furthermore, even in atmosphere, a lot of the reaction in a cartridge takes place inside the cartridge before any external atmosphere can intrude.

 

Even black powder is 75% composed of potassium nitrate: KNO3. Three oxygen atoms are enough to support combustion.

 

However, other issues may come up. People firing bullets in zero g will fly off the

 

Well, the question was "vacuum". Vacuum can occur in gravity (on Luna or Mercury, for instance).

Geez, I've been hanging around lawyers too much. I'm sure "zero-G" was probably implied.

 

become a factor--in naked sunlight, items can be heated up much higher than normal (which could cause rounds to detonate with too much force, rupturing the weapon or otherwise misfiring). Items in shadow can

 

Or the rounds could cook off. That is, they could fire from the heat without the trigger being pulled.

 

 

cool down to really low temperatures--I suspect that the powder might not work if it is cryogenically cold.

 

Good question. I suspect it would work, but I don't know for sure.

[shadowcat1313]

what about the use of gyrojet rounds in a vacumn?

[BoneDaddy]

regarding recoil - if the weapon is integrated to the pressure/0-G suit, the onboard computer could compensate for recoil with a simple thruster adjustment. I would expect any milspec 0-G suit to have such a capacity. (Hmmm... Integrated knockback resistance in zeroG, how handy...)

[Drakkenkin]

quote: shadowcat1313

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what about the use of gyrojet rounds in a vacuum?

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They could be made to work too. You just need to use the correct propellant.

 

Drakkenkin

[Drakkenkin]

Originally posted by BoneDaddy

regarding recoil - if the weapon is integrated to the pressure/0-G suit, the on-board computer could compensate for recoil with a simple thruster adjustment.

 

It could be done, and it's a good idea.

 

The suit would have to have sensors in the arms to know in what vector the gun is being fired. That way it can compensate for the force of the gun being fired in any direction. Even then there may be some areas the trooper may want to fire that the engineers over looked for some reason, or they thought that the trooper would not fire in. Man what a disaster that would be in 0-G.

 

That over site may not last long, but then again it might... ie: If the compainy making the suites can pull the right strings. Bad military equipment has been known to stick around and cures the units that use them.

[Barwickian]

Gauss weapons would also work in a vacuum. You'd still have the problem of recoil in zero-gravity (which a gyrojet wouldn't have), but it could be mitigated by a low-velocity setting (which would, in turn, reduce the damage the weapon does - unless it contains an explosive warhead).

 

Gauss weapons would work in atmospheres with or without oxygen, and in vacuums.

[Kristopher]

Originally posted by AnotherSkip

Graphite, Powdered.

ought to solve it all.

 

the lubricant is dry, does not bond with metals and is easily made, common and easily applied.

 

Graphite powder is not a lubricant in a vacuum. In fact, it's highly abrasive.

[BoneDaddy]

Originally posted by Drakkenkin

It could be done, and it's a good idea.

 

The suit would have to have sensors in the arms to know in what vector the gun is being fired. That way it can compensate for the force of the gun being fired in any direction. Even then there may be some areas the trooper may want to fire that the engineers over looked for some reason, or they thought that the trooper would not fire in. Man what a disaster that would be in 0-G.

 

That over site may not last long, but then again it might... ie: If the compainy making the suites can pull the right strings. Bad military equipment has been known to stick around and cures the units that use them.

 

I think the suit computer has to have two things - gyrostabilizers so the suit can determine the forces being exerted upon it, and a relative position monitor (Its a GPS without a G - needs to be linked to some hard point - the drop ship, the CO, the center of the nearest major planet sized celestial body, etc.) The squeezing the trigger initiates an autocorrect sequence - corrects any added accelleration, puts velocity back where it was before the trigger was squeezed. "Simple" vector physics, I think.

[Drakkenkin]

I think the suit computer has to have two things - gyro-stabilizers so the suit can determine the forces being exerted upon it, and a relative position monitor (Its a GPS without a G - needs to be linked to some hard point - the drop ship, the CO, the center of the nearest major planet sized celestial body, etc.) The squeezing the trigger initiates an auto-correct sequence - corrects any added acceleration, puts velocity back where it was before the trigger was squeezed. "Simple" vector physics, I think.

 

All really good point that needed to be brought up.

 

I think that the gyro-stabilizer would work best in tandem with the sensors I was talking about. The gyro-stabilizer would be more of a reactionary effort while knowing in general where the force would be coming from would be a preparatory effort. The gyro-stabilizer by its self might causing the trooper to get shaken up a bit more as the gun pushes him back and then the suit fires its engines to compensate. I was think that the sensor in the arms would give the on board computer in the suit a heads up for the correction that will be needed, thought it would most likely not be exact. This would allow the suit to make an immediate anticipated corrections while the gyro-stabilizer would work better to fine tune adjustment that is needed.

 

I agree that a PS system (or FPPS Fix Point Positioning System) is needed but I wounder how well it would work in combat. In warfare it would be fair to assume that the enemy would use EW to block the suits ability to get 'see' that fixed point.

 

But over all I agree most of it would be simple vector baced physics.

 

Drakkenkin

 

PS: Kristopher, why do you say that graphite powder would not be a lubricant in a vacuum?

 

Arthur, where did you find the formula C3H5N3O9?

[Starwolf]

Several things should be considered...first recoil may not be as much of a problem as you would think. Most semi-auto/and auto weapons use a blowback mechanism to operate the weapons action and help control recoil. The weight of the weapon also helps to control recoil. And finally the user, if trained properly can use muscle to control recoil. In addition current weapons fire just fine in sub-zero temperatures. Military weapons used in the arctic are first degreased, then they may be fired with no problems. With lead or lead alloy bullets, brass jackets, and steel weapons, I don't think that Vacuum welding will be an issue, as the metals are to dissimilar to bond readily. I believe that a micro-temperature control system to heat/cool the chamber, barrel, and magazine would be more than adequate. Such temperature control technology exists today and is in use in some High-end computer systems, and portable food heating/cooling units.

[Lowly Uhlan]

Originally posted by BoneDaddy

regarding recoil - if the weapon is integrated to the pressure/0-G suit, the onboard computer could compensate for recoil with a simple thruster adjustment. I would expect any milspec 0-G suit to have such a capacity. (Hmmm... Integrated knockback resistance in zeroG, how handy...)

 

Good call. I'll throw that in.

[Outsider]

Regardless of the weapon's internal function, if it works by spitting a bullet at high velocity out of one end, and provides all the accelleration the bullet is going to get while it is inside the gun (ie not a self propelled bullet) it is going to have a action/reaction effect. How strong the person firing the gun is isnt going to matter. Only how much he masses will.

 

Rerouting some of the escaping gasses such that they leave the Gun/Astronaut system in the opposite (or somewhat opposite) direction as the bullet will help reduce, but not eliminate the problem. (muzzlebrakes are good in vaccum!)

 

As to teh problem of rounds cooking off in vaccum, that is pretty easy to solve by having one's gun be included in the astronaut's temperature regulation system, or have its own.

 

Creating cartridges that will stand up to being in vacuum shouldnt be too hard either.