Guns in space

[otomik]

Radiation is addressed in the thermos bottle you described by the silvered glass on the outer layer of the inner bottle. The mirror reflects any radiant heat back into the contents of the thermos, and it also reflects away any radiant heat that might get into the bottle.

I was just thinking about that from an Alton Brown episode.

We haven't developed any projectile based weapons that didn't factor in gravity and atmospheric pressure.

Sure we have, I bet a gyrojet rifle would work great in space, better than it does down the gravity well.

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

the projectile is ignited and leaves the barrel but it doesn't have a lot of energy yet, it's still gaining speed after it leaves the barrel, very little recoil. I bet these mini-rockets would attain very high speeds with no air in the way.

 

[LaEscopeta]

So why wouldn't a gun in space be like a gun in a thermose? There are no air particles bumping into it leaching off heat.

Heat is transferred by 3 methods:
1. Conduction – heat transferred from one material to a second lower temperature material that is touching the first. You touch something hot and get burned, that’s conduction.
2. Convection – heat carried away a moving fluid, like air or water. Wind chill, as explained in post #45 above is convection (although some feel it is only convection if the fluid movement is caused by the heat changing the density of the fluid and causing it to move.)
3. Radiation – Heat leaving a mass by infrared emissions. The heat you feel standing in front of a fire is radiation.

From a gun in space there will be no heat transfer by the first two, only the third. Infrared heat radiates through the vacuum of space just like visible light. How fast the gun loses heat depends on the size, shape and material. But as stated in post #46 and others above, heat would also be absorbed from sun and star light, if the gun was not in the shade (behind a planet, a moon, a space ship, the astronaut holding the gun, etc.) The amount of heat absorbed depends on the size, shape, color, material of the gun, and the distance from the sun/stars.

That’s a whole lot of depends. But if you were close to a sun/star, not shaded, and had a black gun, it would heat up to the point where it would not work. If you were in deep space, in the shade, had a sliver gun (that radiated heat like a black body), it would eventually cool off to the point where it would not work. I suspect there are lots of situations in between where a decently made gun would work just fine. A revolver/bolt/pump gun would work in more situations than an autoloader.

 

[learn2shoot]

Another thought

I wonder what a tracer would do (assuming a oxidizer).

 

[DF357]

If you were in 'free space' outside of earth's orbit and you fired a gun , assuming your bullet isn't drawn into some other space body's gravity, theoretically someone could be hit with a lead slug still travelling at muzzle velocity, hundreds of years into the future.

Future travelling in deep space could be hazardous, if too many spacemen celebrate something by firing their guns into the 'air' !

 

[unspellable]

Too many?

<< Future travelling in deep space could be hazardous, if too many spacemen celebrate something by firing their guns into the 'air' >>

"Too many" is a what physicists refer to as a "large number". Such numbers are usually described in terms of how many hundreds or thousands of zeros they have after them. The universe is a BIG place.

 

[Auslander]

Guess I'll have to use a bolt action rifle with graphite if I ever get a chance to try this....

Graphite doesn't work in space. Graphite is tiny laminar plates of solid carbon. The carbon forms hexagonal rings with each carbon bonded to three other carbon atoms. The rings are jointed edge to edge into larger sheets. The single atom thick sheets are stacked in loosely boned plates of microscopic size. The lubrication effect in graphite is caused by the air trapped between the plates. No air no lubrication.

Early in the space program some engineers though graphite would be the perfect lubricant. They noticed the fly wheels in the gyros in early experimental high altitude craft consumed extraordinary amounts of power. The extra power use led to the early loss of several projects. They conducted vacuum chamber tests and discover their mistake. They use molybdenum disulfide on stuff that they can’t bush with Teflon now.

 

[Jim Watson]

Geez, Cajun, how could you read Tunnel in the Sky without seeking out everything else Heinlein wrote? At least Red Planet, which has ample shooting, though with beam rather than bullet.

There was a story in Galaxy magazine once upon a time. Seems the ETs were dropping their convicts on Luna with minimum but long term life support. (Why? I'd just space 'em rather than haul them that far.) We found ourselves in regular gunfights with alien mobsters as we explored the moon. Firearms were colloquially known as "Swifts." Because the author had calculated that a .220 Swift would make Lunar orbital velocity and he could shoot an assailant in the back after one low orbit pass. Weak, man, weak.

 

[akodo]

Heat is transferred by 3 methods:
1. Conduction – heat transferred from one material to a second lower temperature material that is touching the first. You touch something hot and get burned, that’s conduction.
2. Convection – heat carried away a moving fluid, like air or water. Wind chill, as explained in post #45 above is convection (although some feel it is only convection if the fluid movement is caused by the heat changing the density of the fluid and causing it to move.)
3. Radiation – Heat leaving a mass by infrared emissions. The heat you feel standing in front of a fire is radiation.

So here is my question, waht about space increases the radiant heat gain or loss? Anything?

I mean, radiant heat gain or loss is ALWAYS going on, in addition to any more conventinal heat gain/loss (conductive or convective) I mean, a hot stove burner, you hold your hand over it and feel the radiant heat (although you may feel some convection heat too). You turn the stove off, it takes a while for the burner to loose enough heat through radiant+convection. Heat your earthgun in an earth oven to 300 degrees F, set it out to cool, it would probably take half an hour to drop from 300 back to 75 F, again radiant+convection, so in space, after you heat your spacegun in the spaceoven and float it out the spacehatch to cool, I I think it would take AT LEAST the same amount of time, and probably more, because heat loss is only by radiant loss, none by convection.

IN the same way, I don't think a gun would cool all that fast from 75F degrees to -25F degrees

 

[LaEscopeta]

So here is my question, waht about space increases the radiant heat gain or loss? Anything?

As I understand it, it is not what is in space that changes radiant heat transfer but what isn’t.

The earthgun heated in an earth oven to 300 degrees F and set out to cool is radiating heat and also ABSORBING radiant heat at the same time, from every other mass in the room. There is constant 2-way radiant heat transfer between all the objects in the room, the walls, floor, even the air particles. I know the higher temperature objects are generally emitting radiant heat faster than the cooler objects, but I don’t remember if the temperature of an object is a factor in how fast it ABSORBS radiant heat. But the 300 degree gun is radiating heat faster then it is absorbing it, so it cools off (not to mention convection and conductive heat loss.)

It the vacuum of space, there are fewer objects around a 75 degree F spacegun to radiate heat back to the gun. Like only the astronaut holding the gun, maybe a spaceship, and maybe a close target. The gun it is going to radiate heat at about the same rate as on earth, but with fewer object from which to absorb heat from, it is going to have a greater net heat loss, and will cool off faster (if sun or strong star light is not shining on it.)

IN the same way, I don't think a gun would cool all that fast from 75F degrees to -25F degrees

I don’t think it would cool down particularly fast either. But in the absence of strong sun/star light, it will cool off, eventually close to absolute zero (-573 degrees F?)

 

[Mal H]

"... eventually close to absolute zero (-573 degrees F?)"
Actually, it's closer to -460 deg F. Until you get to intergalactic space will an object as large as a gun get anywhere close to absolute zero. There is too much radiant energy impinging on it anywhere inside the confines of a galaxy from the sun, stars, some planets, etc. Even the background radiation of the universe is still around 3 deg K (-270 deg C) and that's about as close to absolute zero as it gets in the natural world. Physicists have achieved a lower temperature in the lab than is found in space.

 

[Kaylee]

ooh! Thread necromancy!

So say our imaginary spaceman has a rifle and he's tethered to the side of some station or another. He starts out in the shadow if the planet he's orbiting.

Orbit then takes him to the sun side.

1. Will there be a temperature change from that movement that will affect the rifle?

2. Would a reasonable solution to these problems be somehow hooking up the rifle to his EVA suit, whereby some kind of heating/cooling fluid (or whatever) could be run "radiator style" around the critical components of the weapon?

3. Aluminum bits sound easy.. what about the chamber,bolt, and barrel though? Is there some less-sensitive material that's still strong enough to handle those pressures?

 

[44AMP]

Finally....

Someone brought up the other factor, HEAT!

Ok, ammo has "built in air" from the chemical reaction, so it works in space.

OK, we all know about the "cold" of space, but what about the heat of space?

Where does the heat on Earth come from (and don't mention Global Warming-just don't )? It comes from the sun. The same sun that shines on you in space. One of the reasons for the radiators on the space stations is because the sun shines on them. It isn't just the heat generated inside that is the problem.

So, what can happen to your gun (and especially the ammo) when you are in the sun? Could solar heat induce a cookoff? As I understand it, temps in space can go from one extreme to the other, from a several of hundred degrees cold to several hundred degrees hot, depending if you are in the sun, or in shadow. I don;t know what they teach today, but 40 years ago they taught that the sun side of Mercury was hot enough to melt lead, while the dark side was only slightly above the cold of deep space. It seems to me that temps would be the worst problem with using conventional guns and ammo in space.

 

[FieroCDSP]

The real question is will you hear the shot?

If it's a Mosin Nagant, I'm sure you would.

You guys do know there's only one real way to test this idea in all it's forms.

 

[Mark Whiteman]

The shade on the opposite side from the Sun would sink the heat from the other side. I'd be concerned about the cryogenic embrittlement on the cold side. The stress from the temperature difference might have the piece splitting down the sun/shade line!

Actually, a crossbow might be more effective in zero-G...

Necro what?

 

[Kaylee]

Yeah, but if IIRC that one side of Mercury has been getting pretty much consistent sunlight for like a gazillion years- surely some of the reason it's so hot there is that there's no break from the constant "incoming" to bleed off some of its heat.

So for our hypothetical rifle- I assume a goodly deal of its stress is going from that really hot to really cold, yes?

So how do like the attitude thrusters and the like outside the stations and in the shuttle and suchlike handle that problem? I assume they have to contain significantly lower pressures than a firearm, but wouldn't the temp swings still do a number on them?

 

[Mark Whiteman]

I'm pretty sure Mercury would come apart if asked to contain the pressure equivalent of a gunshot. Scaled up to planet size! Even if it was a ball o' steel.

Attitude thrusters are little chambers where little squirts of verrry toxic chemicals mix and react with each other, squirting out the nozzle in a controlled manner. I don't know what pressure they work at, but its no where near 50K PSI. No ignition required. Most everything is protected by something painted white, except the actual nozzle, and thats fairly thin sheet metal of some sort.
I suppose you could rig up a cannon to run on the same chemicals. If you didn't mind wearing a hazmat rig to fire it 10 miles from noplace...

 

[MechAg94]

The differential temperature across the gun would likely cause fit issues if not other problems. The potential low temperatures would cause problems with most types of steel. My employer makes liquid nitrogen, oxygen, and argon. Metals used at -350 F are copper/bronze alloys, aluminum, and some stainless steels. Not sure those stainless steels are good enough to be used in a gun. I guess it is all in the design. It is possible that different propellants could be used in space that wouldn't be considered on the ground due to outdoor conditions. A compressed air gun might be a better choice in some cases. Maybe use a chemical mix to pressure up the tank or just a little chamber in the gun.

As said above, the amount of heat radiated is a function of the temperature difference between the object and the background (the type of surface adds a factor also). Deep space is pretty cold so you would get a lot of heat transfer. However, if the space station is the background, you may not.

 

[jlbraun]

I smell a future Mythbusters show idea!

 

[nobody_special]

Cover the gun with a reflective surface, like polished aluminum (or better yet, gold) foil with a bit of insulation on the inside. Then you have a low thermal emissivity and high reflectivity. As a result, thermal radiation from the sun has a relatively small effect, as does thermal emission to the cold sky.