Firearm Physics Question...

[icebones]

Ok, just for fun, what would it take for a conventional firearm (shoulder fired, or maybe mounted, like a cannon) to fire a projectile into space?

The fasted rifles we have today are only capable of around 4000-4500 fps. at best. and this is nowhere near fast enough

Im not a scientist, but im pretty shure the escape velocity for Earth is around 6.9 miles per second. so a bullet would have to be traveling 5280 feet per second to be equilivent to 1 mile per second.
this means we have to accelerate a projectile upwards of 36960 fps to acheve escape velocity... although you have to conpensate for the bullet slowing down due to gravity and drag. so it would need to be much faster.

given there is a limit to how fast conventional smokeless powder can accelerate a bullet. ive heard it has something to do with the sound barrier and the propellant can only burn as fast as the air around it will compress, or something along those lines.

now, im shure it might be possible to fire a bullet into space using a rail gun, i rember seeing a prototype gun the navy was working on that could fire a 7lb projectile at almost 7 times the speed of sound.

also, im shure some of you have heard of the light gas gun built by NASA to replicate high speed impacts of metiors and other space debris.

would it be possible to fire a projectile from the survace of the earth into space?

 

[Second Amendment Liberal]

do you mean as a sort of defense cannon if ships enter "earth airspace"? i'm a little rusty in science but since gunpowder relies on a chemical reaction, I think it is limited to the speed of sound. gauss and rail guns are theoretically better, but there hasn't been much luck with them.

 

[ShadyScott999]

If my memory is correct (always questionable) it takes about 31.3 x speed of sound to reach escape veloicty. So the mach 7 rail gun won't cut it.

 

[mgkdrgn]

The problem here is having that pesky atmosphere in the way.

The problem with any "gun" (chemical, electro-rail, whatever) is that your acceleration stops the moment you leave the gun, and you then begin to decelerate. Hence, you must be going much faster than escape velocity when you leave the gun, to account for the deceleration that you'll get from the atmosphere.

That kind of velocity, IN the atmosphere, is going to produce two byproducts:
1) one hell of a sonic boom / shock wave
2) a hell of a lot of frictional heating

We won't even go into surviving the Gforces involved in accelerating to that kind of speed over the length of the gun.

 

[expvideo]

Are you saying that when I empty a mag at the moon, the bullets don't hit it?

 

[hankdatank1362]

So astronauts have to travel 6.9 miles per second (36,432 feet per second) in order to escape Earth's gravity?

That's really freaking fast. I mean, I knew they pulled serious G's, but that's REALLY fast. Like almost unbelievable, literally.

 

[heron]

I don't think it could be done, at least not with anything we'd recognize as a typical firearm.

In order to break orbit -- or even achieve orbit -- the projectile has to exceed the acceleration of gravity, which is 32 ft/sec/sec. Note that this is not a velocity, it's an acceleration. A bullet is going as fast as it ever will at the instant it leaves the muzzle; it does not continue to go faster (accelerate). This is why we need rockets to get into space.

I'm sure someone has long since run the calculations to achieve this; after all, they aren't that hard if you know the math (I've forgotten mine) and the question is at least as old as Jules Verne, and probably older by quite a bit. Therefor, if a solution could be engineered, we'd have been using it. No one ever has, afaik, so the engineering has to be either impossible, or so expensive as to not be worth it. I'm guessing the latter.

Here's something helpful:

http://en.wikipedia.org/wiki/Escape_velocity

 

[jackstinson]

This is actually fairly accurate on the subject: http://en.wikipedia.org/wiki/Escape_velocity
The Space Shuttle goes from 0 mph to 17500 mph in 8.5 minutes. For ships, speed is not the factor, but constant propulsion. SpaceShip One only exceeding Mach 3 after a 15 second burn, but went to the edge of space. However it started in-flight from a mothership.

Impey Barbicane might have a better answer.

 

[Eightball]

I thought I read somewhere that powder-operated firearms have an absolute limit of ~6000 FPS, because beyond that the gas cannot expand at an equal or faster rate than that of the projectile--and it would take a massively inefficient amount of powder to even achieve the ~6000fps.

So, whatever it was, would by default not be able to be a powder-actuated design.

 

[chris in va]

*Caution* thread drift question.

I've often wondered...if the Space Shuttle guys theoretically fired a rifle at the Earth, would the bullets heat up enough to cause mini-meteors seen from the ground? I suspect they would have to be made of something like tungsten to survive longer than a split second.

 

[Gungnir]

Escape velocity of Earth is approx 42,949 ft/s (Mach 34 approx) note this is assuming no drag from atmosphere. Actual Escape velocity would be much higher since there would be very appreciable drag in the lower atmosphere. Firing a cannon to achieve this would need a 61,000 g (approx) acceleration.

This is un-powered, and will depart the earth (hence escape velocity) interestingly the drift velocity of Hydrogen atoms is greater than this, so Hydrogen gas eventually leaves the earth into space if released from containment.

Powered launch for instance the Space Shuttle has max V at main engine cutoff that being 24,286 ft/s. But anything can depart the planet if it can maintain a vertical acceleration of 33 ft/s^2

Is it possible yes, it's just a matter of power, do we have the technology right now? I don't think so, a Rail Gun seems the most likely candidate to generate the needed acceleration, but the power needed would be significant, even for a small projectile, either as a burst acceleration, or using a long rail. Not sure which would be more efficient, burst you need to deliver the energy in as short a time as possible, but long rail you waste energy to drag, and friction.

Now once you start to achieve altitude then the escape velocity begins to drop significantly (as you're climbing the earths gravity well), at 9,000 km (to steal Wikipedia) its only roughly 7.1 km/s.

 

[VegasGeorge]

I think Jackstinson is on the right track. The deal with the space bullet is that all of its propulsion takes place at one time. That would have to be one heck of a bang. I think it must be theoretically possible, after all when a large asteroid hits a planet, debris from the resulting explosion can get thrown into space. But, even the largest navel and rail cannon couldn't throw a shell into orbit.

 

[Tommygunn]

The problem with any "gun" (chemical, electro-rail, whatever) is that your acceleration stops the moment you leave the gun, and you then begin to decelerate. Hence, you must be going much faster than escape velocity when you leave the gun, to account for the deceleration that you'll get from the atmosphere.​

Hey, Jules Verne did it. Of course, it required a HUGE cannon and an equally huge suspension of disbelief!

 

[Mal H]

Considering the actual original question:

Ok, just for fun, what would it take for a conventional firearm (shoulder fired, or maybe mounted, like a cannon) to fire a projectile into space?

The answer is it can't be done (at least not with my shoulder!), and not with any conventional cannon. Do we have the means to fire a projectile into space today? I think so, and some of the unconventional "cannons" that might be able to do it have already been mentioned.

You see, the question asks about firing a projectile into space, not necessarily escaping from the earth's gravity. Space is generally agreed to start at around 62 miles up (it's a gradient so there is no clear atmosphere-space boundary), so the task isn't nearly as daunting as getting a projectile to escape the earth altogether and hit the moon.

 

[everallm]

First thing is we have to split the question into 3 different parts

Are you talking about

1. Firing an object that can kiss "space", generally agreed to start at an altitude of 100km

2. Firing an object to reach orbit at an altitude of no less then 100km

3. Firing an object with sufficient velocity it reaches local terrestrial escape velocity

Three very different energy profiles

In the first you need a vertical initial velocity sufficient so that you decelerate to effective zero at 100km and then fall back under gravity.

In the second you are launched at a sufficient velocity and angle that at an altitude of 100km you will "fall" into a (reasonably) stable low earth orbit

In the third you have sufficient end velocity AFTER deceleration due to gravity you leave the gravitational pull of the earth (but not the solar system).

To give yourself some "free" energy, shoot from the equator.

 

[ants]

Imagine being fired in an Impey Barbicane type cannon, sitting in the carriage with such insane acceleration.
I wonder if your ears can even hear your mouth scream?
After you land, you sit around in silence until your own screams finally reach you.

 

[LoneCoon]

Getting the projectile into space isn't the problem. You could, in theory, fire a projectile out of a cannon /railgun to get a decent initial velocity, then cut in with a rocket to get you the rest of the way there. Your problem comes in insulating your projectile against the massive G forces of the initial cannon.

It's way more efficient to shoot stuff back AT earth then out from it.

 

[everallm]

The physics and practicalities of using a chemical as opposed to electrical solution were solved during WW2 by the Germans with the V3 weapon which was to be a cannon capable of bombarding London from France.

The tube has multiple side mounted firing chambers along the length to progressively boost the projectile as it traveled the length of the cannon. Because of the look it was codenamed The Millipede

http://en.wikipedia.org/wiki/Mimoyecques

 

[Ragnar Danneskjold]

Not to mention, that even if you build up enough speed and energy to leave the atmosphere, is your projectile going to have enough momentum to actually damage the target?

 

[jerkface11]

Google Gerald Bull.

 

[Hawk]

Google Gerald Bull.

...and project HARP.

http://en.wikipedia.org/wiki/Space_gun

 

[benEzra]

I've often wondered...if the Space Shuttle guys theoretically fired a rifle at the Earth, would the bullets heat up enough to cause mini-meteors seen from the ground? I suspect they would have to be made of something like tungsten to survive longer than a split second.

Assuming the bullet actually entered the atmosphere, yes, it would make an impressive meteor, and it would probably last several seconds.

Most "shooting stars" you see are sand-grain size to pebble size (albeit traveling considerably faster than mere low-earth-orbit velocity), so a bullet would be in that size range.