Bullets in vacuum?

[Metaphysician]

Perhaps rounds designed so that temperature is not the triggering mechanism??

[Al_Beddow]

Ok, I've been enjoying this thread and carefully paying attention to what is being said.

 

First one needs to remember one of Newtons laws "every action produces an equal and opposite reaction". Unless you are firing something like an energy only weapon, there is going to be force exerted to move the projectile out of the weapon. That same force will be excerted back against the weapon and henceforth against whatever (or whoever) was holding the weapon.

 

Normally, like on a planet with a reasonable amount of gravity, this isn't too much of a problem. The person holding the weapon (since that is what we're talking about) can "brace themselves" on the ground thanks to gravity.

 

Unfortunately in space there is no gravity. Even if you were standing on the hull of a ship, if you didn't have something holding you to the hull of the ship, then when you fired a projectile weapon there would be nothing to hold you in place. The force may not move you much, but it would get you moving.

 

The ideas of a compensation system (to counter the force of the weapon being discharged) is a great idea. In fact a system that just uses the stars to keep you stable would work (system notes the stars in relationship to your current position and unless you used the suits controls to chang your position, it re-establishes you back to your position relative to the stars).

 

The biggest problem for such a system is the depth of the programming needed to make it work effectively.

[Metaphysician]

Well, if the gun is consistent in terms of force it generates, the compensator could just operate off the firing mechanism with a fixed compensation. Might not be perfect, but close enough for most purposes.

[Starwolf]

How strong the person firing the gun is isnt going to matter. Only how much he masses will.

 

This is true to a certain extent. I am an accomplished marksman having earned Expert medals in both pistol and rifle from the US Navy. I am also a closet gunsmith having completed a correspondence course in gunsmithing. When I spoke of muscle control, I was perhaps not very clear. There is very little of brute strength to weapons control. In my experience teaching firearms use, the worst marksmen are those that attempt to use pure brute strength to control the weapons recoil.

 

The thing to remember is that our arms and wrists are flexible. When I mentioned muscle control, I was referring to the technique of using muscle control as a sort of built in spring or flexing action to counter act recoil. This is a very real method used by expert marksmen to control recoil of large caliber weapons. If you add this technique to advanced porting of gases, a high tech blowback action mechanism, and counter weights on the weapon itself to add mass, it should be more than sufficient to counter act the reverse motion effect in zero-g.

 

By the same token by simply stiff arming the weapon when fired you can force the very reaction we have been discussing.

[tmutant]

Originally posted by zarglif69

But not airtight.

 

Modern ammunition is both air and water tight.

 

Electrically primed ammunition is currently available commercially. A variation on this may solve the over heating problem by requiring more than simple heat to ignite the propellent. A combination of ceramic and multiple metals would overcome vacuum bonding. Currently, aluminum, scandium, titanium, various steel alloys, brass, fiberglass, and thermo-stable plastics are used in firearms construction. Variations on these would solve most of the temperature problems independent of the need for a space suit for the gun. Recoil is another matter. A reaction control system is possible, but might have to be extremely complex to work. Somebody could, on the other hand, come up with a ludicrously simple solution that no one has thought of yet.

[Zeropoint]

This is true to a certain extent. I am an accomplished marksman having earned Expert medals in both pistol and rifle from the US Navy. I am also a closet gunsmith having completed a correspondence course in gunsmithing. When I spoke of muscle control, I was perhaps not very clear. There is very little of brute strength to weapons control. In my experience teaching firearms use, the worst marksmen are those that attempt to use pure brute strength to control the weapons recoil.

 

The thing to remember is that our arms and wrists are flexible. When I mentioned muscle control, I was referring to the technique of using muscle control as a sort of built in spring or flexing action to counter act recoil. This is a very real method used by expert marksmen to control recoil of large caliber weapons. If you add this technique to advanced porting of gases, a high tech blowback action mechanism, and counter weights on the weapon itself to add mass, it should be more than sufficient to counter act the reverse motion effect in zero-g.

 

No.

 

Conservation of momentum dictates that if the shooter/gun/bullet system has zero momentum before the shot is fired, the the system will have zero momentum after the shot is fired. That means that however much momentum the bullet has, the shooter and gun will have the same amount in the opposite direction.

 

Looking at it another way: That bullet started out stationary, and ended up moving at a high speed. That means it experienced acceleration, and that means that it experienced a net non-zero force for some non-zero length of time. Sir Isaac Newton (do they still teach people about him these days?) observed that "All forces in the universe occur in equal but oppositely directed pairs." This means that if a force existed acting on the bullet to move it forward, then somewhere, something was acted on by a force to move it backward (i.e. in the opposite direction that the bullet was fired.) That thing is the person doing the shooting.*

 

It doesn't matter if you stiff-arm the gun or let your arm flex; an unbalanced force was applied to you. You are now moving and will continue to move unless and until you experience another force which delivers a total impulse (force times duration; pushing half as hard for twice as long yields the same change in velocity) equal to the recoil.

 

Zeropoint

 

* Well, it's actually the gasses in the barrel. Which exert a force on the slide (assuming a blow-back action for simplicity's sake) which exerts a force on the recoil spring, which exerts a force on the frame, which exerts a force on the shooter's hand, which exerts a force on the shooter's wrist, which etc, etc.

 

It's a lot easier just to look at the steady-state conditions which exist before and after the whole firing-and-absorbing-recoil event.

 

EDIT: check out http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html for a well-orgaized discussion of pretty much the entire field of physics.

[Outsider]

Zeropoint is talking about what my point was.

 

The overall Shooter+Gun+Bullet+Propellant momentum before shooting has to balance with the Shooter+Gun+Bullet+Propellant momentum after shooting.

 

If all is stationary, then adding a net vector in direction (A) to the bullet has to be balanced out by adding a net vector to everything else equal to (-A).

 

Given that our goal is to keep Shooter+Gun stationary, the only thing to do is put the (-A) vector onto the Propellant. Or, I suppose, simultaneously shoot another bullet in the opposite direction

[tmutant]

Originally posted by Outsider

Zeropoint is talking about what my point was.

 

The overall Shooter+Gun+Bullet+Propellant momentum before shooting has to balance with the Shooter+Gun+Bullet+Propellant momentum after shooting.

 

If all is stationary, then adding a net vector in direction (A) to the bullet has to be balanced out by adding a net vector to everything else equal to (-A).

 

Given that our goal is to keep Shooter+Gun stationary, the only thing to do is put the (-A) vector onto the Propellant. Or, I suppose, simultaneously shoot another bullet in the opposite direction

 

Or use a computer controlled thruster pack with stellar navigation sensors to keep the shooter stationary while shooting. Someone mentioned it earlier in the thread. Sweden makes a rocket launcher, the Armbrust, that uses an ejected counter-weight of styrofoam pellets to counteract recoil from the short-impulse rocket motor. It's not dangerous to stand behind it, unlike most rocket launchers. Something similar might be worked out for a firearm used in space.

[Zeropoint]

I've read about recoilless rifles that work by turning the back end of the chamber into a rocket nozzle, creating a high-speed jet of gas which balances the recoil of the projectile. I don't know if they achieve an exact balance, though, and you'd need to have the jet move past you, so it wouldn't work for a pistol. The real ones are over-the-shoulder models.

 

Zeropoint

[Nyrath]

Re: Bullets in vacuum?

 

I've read that the recoil from a sidearm in microgravity is over-rated. People who did the math said that if you were unbraced, a .45 automatic would only give you about three degrees per second of rotation. If you plus your suit had a mass of about 50 kilograms, each bullet would give you a measly 0.12 meters per second of acceleration.

 

Another thing to keep in mind: a sidearm meant to be used while space suited will have to have an over-sized trigger guard to allow insertion of a space-gloved finger.

 

More at my web site

 

I hope this helps.

[Ternaugh]

Re: Bullets in vacuum?

 

I've read that the recoil from a sidearm in microgravity is over-rated. People who did the math said that if you were unbraced, a .45 automatic would only give you about three degrees per second of rotation. If you plus your suit had a mass of about 50 kilograms, each bullet would give you a measly 0.12 meters per second of acceleration.

 

Another thing to keep in mind: a sidearm meant to be used while space suited will have to have an over-sized trigger guard to allow insertion of a space-gloved finger.

 

More at my web site

 

I hope this helps.

 

That doesn't sound bad. It means, however, that the person that you were aiming at would then be at your back in 60 seconds(60s * 3 degrees/s). Oh, and you would have drifted 7.2m away from your original position. Of course, that's just for one bullet. Did you empty the clip? That would increase the rotation to 21 degrees/s (you rotate completely every 17.14 seconds, and show your backside to your enemy for half of that time), and a drift rate of approximately .84m/s (every minute uncompensated by thrust in the opposite direction moves you 50m away from the battle). I, for one, would rather have the computer-compensated thrust to counteract this.

 

JoeG

[Old Man]

Re: Bullets in vacuum?

 

Gyrojet oughta work just fine, since it's basically solid rocket fuel, and I'm pretty sure solid rocket fuel works in space...

[DrFurious]

Re: Bullets in vacuum?

 

Just to point out some physics clarifications...

 

Normally' date=' like on a planet with a reasonable amount of gravity, this isn't too much of a problem. The person holding the weapon (since that is what we're talking about) can "brace themselves" on the ground thanks to gravity.[/quote']

 

That's friction actually - friction acts to oppose the direction of motion (in this case, the motion of the body backwards).

 

Unfortunately in space there is no gravity. Even if you were standing on the hull of a ship' date=' if you didn't have something holding you to the hull of the ship, then when you fired a projectile weapon there would be nothing to hold you in place. The force may not move you much, but it would get you moving.[/quote']

 

Your analysis is essentially correct but note that there IS gravity in space. While you may be weightless, gravity is still acting upon you. You are weightless in orbit not because there is no gravity, but because you are falling towards the earth at the same rate that the earth's surface is dropping away from you.

[Nyrath]

Re: Bullets in vacuum?

 

Your analysis is essentially correct but note that there IS gravity in space. While you may be weightless' date=' gravity is still acting upon you. You are weightless in orbit not because there is no gravity, but because you are falling towards the earth at the same rate that the earth's surface is dropping away from you.[/quote']

Absolutely. For that reason I prefer the term "Freefall" to "zero-gravity".