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Cabercatcher
01-26-2008, 02:33 AM
I am curious about Newton's Third Law (For every action, there is an equal and opposite reaction.)

I know that when fired, the bullet would behave just as Cecil described. Even when taking mass into consideration wouldn't the "gun-slinger" be on fast trip in the opposite direction? Or... Do I need a refresher course in physics?

CaberCatcher

Malacandra
01-26-2008, 03:20 AM
The gun-slinger has recoil to worry about, but he and the gun put together have a much larger mass than the bullet. The "equal and opposite reaction" is that he and the gun between them have a momentum exactly equal and opposite to the bullet. Since momentum equals velocity times mass, if the firer has (say) ten thousand times the mass of the bullet, he'll acquire a velocity one ten-thousandth that of the bullet. A seriously quick bullet departing the scene at 1km per second sees the firer heading the other way at 10cm per second. So delete "fast", insert "slow", and you're dead right.

The mass ratio stated above would be a 100kg firer and a 10g bullet - that's about 220 pounds versus a third of an ounce, roughly. Not necessarily spot on but in the ballpark.

bibliophage
01-26-2008, 09:04 AM
Hey there, Cabercatcher. The gun-in-space item is a staff report written by Bricker, one of Cecil's assistant, not by Cecil himself. So I'll move this thread to the Comments on Staff Reports forum.

Also, a link to the item you're commenting on is appreciated. This is the one: Would a gun work in space? (http://www.straightdope.com/mailbag/mgunsinspace.html)

OtakuLoki
01-26-2008, 09:17 AM
Also, a link to the item you're commenting on is appreciated. This is the one: Would a gun work in space? (http://www.straightdope.com/mailbag/mgunsinspace.html)

bibliophage? I think you have the wrong link there - at least I'm kinda surprised to imagine Bricker involved in something called "The Monkey Chow Diaries." And I wonder where the SDSTAFF report might be on that page. ;)

(And if I can be so bold - what on earth brought you to that page?)

01-26-2008, 09:24 AM
Who knew Bricker was a goofy 20 something trying to subsist on a diet of Monkey Chow...

Gfactor
01-27-2008, 11:33 AM
I've corrected the links. They now go to Bricker's article instead of The Monkey Chow Diaries.

Gfactor

Gfactor
01-27-2008, 12:49 PM
And by the way, great report, Bricker.

puppygod
01-28-2008, 10:12 AM
The gun-slinger has recoil to worry about, but he and the gun put together have a much larger mass than the bullet. The "equal and opposite reaction" is that he and the gun between them have a momentum exactly equal and opposite to the bullet. Since momentum equals velocity times mass, if the firer has (say) ten thousand times the mass of the bullet, he'll acquire a velocity one ten-thousandth that of the bullet. A seriously quick bullet departing the scene at 1km per second sees the firer heading the other way at 10cm per second. So delete "fast", insert "slow", and you're dead right.

The mass ratio stated above would be a 100kg firer and a 10g bullet - that's about 220 pounds versus a third of an ounce, roughly. Not necessarily spot on but in the ballpark.

Yeah. What he said.

I've crunched numbers and shooting single bullet from 9mm pistol would propel me with extreme speed of 0.15 mph, rounded. Even emptying whole magazine from a Glock wouldn't propel me with speed that I would call fast.

Elendil's Heir
01-28-2008, 10:56 PM
I've read that the Soviets stashed some small arms aboard their spacecraft during the Cold War, but more to defend themselves against critters upon landing (they always parachuted down over land, sometimes in pretty remote areas of the USSR or its dependencies) than to fight American astronauts. As far as I know, no one's ever fired a gun in space.

Sleel
01-29-2008, 01:31 AM
A bigger consideration would be that unless the firearm is held close to the center of mass (just slightly south of the navel, on most men, almost in between the hips on women) you'll start to tumble. Granted, the energy we're talking about is, as earlier posters noted, not that high, but it will have a much bigger effect on your attitude in space than you'd expect if you were only considering how much it would move your entire mass. After a couple of shots, you'd probably have to reorient yourself.

Hostile Dialect
01-29-2008, 03:56 AM
Only against aliens who speak English.

Pushkin
01-29-2008, 05:51 AM
As far as I know, no one's ever fired a gun in space.

Cosmonauts were expected to land in the wilderness and be prepared to defend themselves against the worst that Russian wildlife could throw at them. They have a triple barrelled gun (http://suzymchale.com/kosmonavtka/trainsurv.html) for this purpose;

There is a gun on board, designated ТП-82, TP-82. It is a three-barrel pistol that can be used for firing signals and shooting game. The two upper barrels are smooth-bore firing 12.5 mm cartridges; the lower barrel is rifled and fires 5.45 mm bullet cartridges. The machete provided in the NAZ survival kit can be utilized as a butt for the gun.

But the USSR did have at least one armed station in orbit, Salyut 3 (http://en.wikipedia.org/wiki/Salyut_3#.22Self-defense.22_gun). The gun was allegedly tested after the crew returned to Earth and the station was due to be deorbited.

Chefguy
01-29-2008, 10:07 AM
Bricker's article claims that space has no temperature. I must confess I can't get my head around that concept. So what happens to thermometer if you take it into deep space. Does it lose its mind?

soffty
01-29-2008, 10:12 AM
Chefguy, I have been to space, symbolically, so maybe that answers your question, as I do feel like a thermometer on this forum.

OtakuLoki
01-29-2008, 10:24 AM
Chefguy, the place to begin is with a definition of what temperature really is: It's a measure of the average kinetic energy (brownian motion) of the molecules in a given substance. Since a vacuum, which is what space is, lacks molecules, it can't have any temperature, itself.

(I'm simplifying, here - at the edges of things this definition breaks down - but it'll work for the basics.)

What your thermometer will be measuring then, isn't a temperature of a surrounding environment, so much as it's own response to the radiation impinging upon it, or the radiation it's giving off. In direct sunlight, for example, the thermometer will probably read a very high temperature, because it would be receiving so much more radiative energy than it would be broadcasting.

carnivorousplant
01-29-2008, 10:30 AM
How much force did the compressed air gun used for Gemini spacewalks produce?

Pushkin
01-29-2008, 10:56 AM
How much force did the compressed air gun used for Gemini spacewalks produce?

That reminds me of the quiz Dad had on a team building exercise, you were given a list of things found in a life boat, on the moon etc and uses for them were asked for. A pair of handguns were useful in space to help you move about the moon, point them in the opposite direction of travel and pull the trigger. How a pair of hand guns got to the moon in the first place was never raised.

Baldwin
01-29-2008, 11:23 AM
That reminds me of the quiz Dad had on a team building exercise, you were given a list of things found in a life boat, on the moon etc and uses for them were asked for. A pair of handguns were useful in space to help you move about the moon, point them in the opposite direction of travel and pull the trigger. How a pair of hand guns got to the moon in the first place was never raised.Well, if you were actually on the Moon, the handguns wouldn't be very useful for transportation, a lot easier to just walk. (Or rather, proceed in short hops, as all the Apollo astronauts adapted to; why did that sliding backwards dance step ever get called the "moonwalk"? No resemblance.)

Did Dick Tracy wear his piece when he was playing golf on the Moon?

Elendil's Heir
01-29-2008, 12:15 PM
...Did Dick Tracy wear his piece when he was playing golf on the Moon?

I'm sure he did. You never know when, and where, Flattop might try to put a hit on you.

Chefguy
01-29-2008, 12:46 PM
Chefguy, the place to begin is with a definition of what temperature really is: It's a measure of the average kinetic energy (brownian motion) of the molecules in a given substance. Since a vacuum, which is what space is, lacks molecules, it can't have any temperature, itself.

(I'm simplifying, here - at the edges of things this definition breaks down - but it'll work for the basics.)

What your thermometer will be measuring then, isn't a temperature of a surrounding environment, so much as it's own response to the radiation impinging upon it, or the radiation it's giving off. In direct sunlight, for example, the thermometer will probably read a very high temperature, because it would be receiving so much more radiative energy than it would be broadcasting.

So if the thermometer was in a box of some sort (lead?), where there were no external radiation impinging upon it?

OtakuLoki
01-29-2008, 12:55 PM
So if the thermometer was in a box of some sort (lead?), where there were no external radiation impinging upon it?

IANAPhysicist, so take this with some cautions.

After the box radiated off it's excess energy, from being placed there, it would eventually come to equilibrium at what is sometimes called "the temperature" of space. Actually, AIUI, this is simply a measure of the heat energy remaining from the Big Bang (or whatever the creation of the universe might have been). It's what was measured first in the 60s using radio telescopes, and is about 2. something degrees above absolute zero. According to Wikipedia it's called Cosmic microwave background radiation (http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation).

But that's assuming your thermometer can read that low a temperature. Currently, AIUI, there is no single thermometer that actually is useful for reading temperatures at the human scale, say 273 K, going down that low.

Again, if anyone with better knowledge of this stuff cares to correct me, I know I'm playing fast and loose with definitions and explainations - it's just meant to be sunday supplement level stuff.

II Gyan II
01-29-2008, 01:56 PM
On a tangential note, Bricker claims:

People typically think of space as cold, but in fact space, being a vacuum, essentially has no temperature at all

but that's neither here nor there.

'Cold' & 'hot' refers to a perceptual quality. 'Temperature' is a measure of energy. Unless thermoception is completely missing when in space, an exposed human will register some quale, and I'm guessing, will feel cold.

OtakuLoki
01-29-2008, 02:03 PM
'Cold' & 'hot' refers to a perceptual quality. 'Temperature' is a measure of energy. Unless thermoception is completely missing when in space, an exposed human will register some quale, and I'm guessing, will feel cold.

I'd wager that much of the perception of cold would be from the evaporative cooling as fluids boil off (and from) the outer tissues. Which would be an artifact, not of space's inherent heat or cold, but rather a transient effect being felt as your body responds to the change in pressure.

In the interests of science, I'll let you volunteer to tell us what it really feels like. ;)

tim314
01-29-2008, 02:17 PM
Bricker's article claims that space has no temperature. I must confess I can't get my head around that concept. So what happens to thermometer if you take it into deep space. Does it lose its mind?
Chefguy, see if this helps: A thermometer, whether in space or on earth, only measures its own temperature. It's just that if you stick the thermometer under your tongue, the exchange of heat between the thermometer and your body results in the thermometer being at the same temperature as your body.

Space itself doesn't have a temperature per se, because temperature is a property of matter, of "stuff" so to speak. When people talk about the "temperature of space", they really mean "the temperature stuff ends up at if you put it in space." The thermometer would measure whatever temperature it ended up having based on how much sunlight it was absorbing and other factors like that.

SlowMindThinking
01-29-2008, 02:23 PM
Since I seem to have beat Chronos to reading this thread, I'll be the standard physicist.

OtakuLoki is more or less correct, with some minor corrections. Temperature is a measure of the average kinetic energy of whatever particles you are interested in (the molecules in the atmosphere surrounding you, the molecules in your pool, etc.) Even in a solid, the atoms, or molecules, or what have you are moving. (This motion is not Brownian motion, however.)

You don't have to worry about putting your thermometer in lead. The radiation of which OtakuLoki speaks is mostly light and infrared, etc. So, you can shield the thermometer by putting it in the shade.

Finally, you might wonder how space can have no temperature and a temperature of 3.2 Kelvin (3 degrees Centigrade above absolute zero.) Bricker simply simplified. Even in space, there are photons and neutrinos and who knows what else flitting about. The photons are at a temperature of 3.2 K. For all practical purposes, neutrinos do not interact with your thermometer, or you, so they don't count.

Hostile Dialect
01-29-2008, 02:27 PM
I'd wager that much of the perception of cold would be from the evaporative cooling as fluids boil off (and from) the outer tissues. Which would be an artifact, not of space's inherent heat or cold, but rather a transient effect being felt as your body responds to the change in pressure.

So, if someone were to survive exposed in space long enough for this transient effect to wear off, would they feel cold?

John W. Kennedy
01-29-2008, 02:49 PM
In Would a gun work in space? (http://www.straightdope.com/mailbag/mgunsinspace.html), we read:The primer is ignited by the mechanical action of the hammer hitting its firing pin (or, in a rimfire cartridge, of the striker hitting the rim);....Ummmm....

No.

Although such "pinfire" weapons and matching cartriges were were made from 1828 to the mid-1880s (more in Europe, especially France, than the US), and the mechanism is still used for watchfob novelty guns (2mm or so), the normal cartridge, since the 1850s, has been either rimfire or centerfire. In both of these designs, the firing pin is part of the hammer, or is hit by the hammer, or is sprung directly, without any hammer. In no case is it part of the cartridge.

The basic difference between rimfire and centerfire is that centerfire economizes on the primer by putting it in a cup in the center, and is therefore used in most large calibers, whereas rimfire puts it all over the back of the shell, and is used in most small calibers, where the centerfire cup would be too fiddly to manufacture. Pinfire, on the other hand, strikes a pin that sticks out at right angle from the cartridge, which avoids the problem of making part of the cartridge soft, but is itself fiddly to make, fiddly to load, and somewhat fragile. Pinfire should not be confused with the roughly contemporary needlefire, in which a long firing pin penetrates the cartridge to strike a primer sitting on the back of the bullet. This had the advantage that the mechanism provided a nice anvil to strike the primer against, but the disadvantage that the needle tended to break or go out of alignment.

Gfactor
01-29-2008, 02:57 PM
In Would a gun work in space? (http://www.straightdope.com/mailbag/mgunsinspace.html), we read:Ummmm....

No.

Although such "pinfire" weapons and matching

I merged this thread with the existing one on the same staff report.

Gfactor
General Questions Moderator

appleciders
01-29-2008, 06:20 PM
Well, if you were actually on the Moon, the handguns wouldn't be very useful for transportation, a lot easier to just walk.
If we're talking about the exercise I think we're talking about, you were given a list of items available to you and prioritize what to carry when your ship crashed and you had to hoof it to the base. The handguns were quite low on the list, since as you surmised, they wouldn't have much use, but they were higher than a couple of things, like matches.

Xema
01-29-2008, 09:14 PM
... whereas rimfire puts it all over the back of the shell, and is used in most small calibers
I know of only one common rimfire caliber: .22. Are there other small calibers that use this scheme?

Princhester
01-29-2008, 09:45 PM
So, if someone were to survive exposed in space long enough for this transient effect to wear off, would they feel cold?

It depends.

The person is going to radiate heat at a certain rate dependant on how warm they are, what colour they are, what they are wearing etc. Broadly, a body at normal temperature is not going to radiate heat very fast.

At the same time, they are going to be warmed by whatever source of radiation they are exposed to. If the Sun was shining on them they'd get somewhere between a little and a lot of heat, depending on distance, for example. If they are in shade or in deep space away from any radiation source, not so much.

The net result of input and output of radiation could be either warming or cooling.

carnivorousplant
01-29-2008, 09:50 PM
The net result of input and output of radiation could be either warming or cooling.
The Apollo spacecraft continually rolled to warm the side towards the sun and cool the other and regulate temperature. It also generated heat from fuel cells.

Chronos
01-29-2008, 11:59 PM
OtakuLoki is more or less correct, with some minor corrections. Temperature is a measure of the average kinetic energy of whatever particles you are interested in (the molecules in the atmosphere surrounding you, the molecules in your pool, etc.) Even in a solid, the atoms, or molecules, or what have you are moving. (This motion is not Brownian motion, however.)Actually, the concept of temperature can be extended past that. The simplest generalization is to say that if two objects are in thermal equilibrium with each other, they're the same temperature. So, for instance, if you put a thermometer next to a black hole (in an otherwise-empty universe; no microwave background radiation or the like), the thermometer will eventually reach a particular temperature (above absolute zero) and stay there. That temperature can be said to be the temperature of the black hole, despite the fact that a black hole has no component particles to vibrate.

Note also that when people refer to the 3 Kelvin background as the "temperature of space", they mean deep space, far away from everything. Close by a star, the star's output will far overwhelm any contribution from the background. An object in Earth orbit or the vicinity (which includes the Moon, the furthest from Earth humans have ever been) will have an equilibrium temperature in the vicinity of the temperatures you find on the Earth. This should be no great surprise, since the Earth itself is an object in space at thermal equilibrium.

puppygod
01-30-2008, 03:36 AM
I know of only one common rimfire caliber: .22. Are there other small calibers that use this scheme?

Well, first of all, there are a lot of various .22 - apart from .22 LR, there is .22 short and .22 WMR and some others, less popular. There is also .17 HMR. Compared to uber-popular .22 LR all other are rare, but they do exist.

si_blakely
01-30-2008, 04:53 AM
A gun will fire in space - but how many times?

Between the thermal expansion issues and the evaporation of lubricants, could you get a full clip off with an AK47 before the thing jams, overheats or just explodes?

Si

puppygod
01-30-2008, 07:02 AM
My WAG would be yes.

Well, evaporation of lubricants would be IMHO biggest concern, but it takes time. On the other hand, it's almost unrelated to actually firing - just exposition to vacuum do. So I think that straight from airlock - shooting without problem. Already in the vacuum for days, might not be able to fire at all.

Overheating wouldn't be issue - barrel is massive enough to soak heat from a single magazine of ammo fired. It gets hot, but not enough to cause problems. Now after half dozen of emptied magazines things gets less rosey. There would be increasing chance of jams and self-ignition, as well as lower accuracy and MUCH faster wear of barrel.

Explode? No. Probably. AK-47 is gas operated, and I'm not sure if higher difference between propellant gases in cylinder and NO atmosphere outside could cause faster wear and/or breaking of parts. Maybe. Also, faster rate of fire.

So, I think that straight out of airlock you could fire a magazine or few from your AK-47, but after that it would be in bad shape - possibly worn and damaged, and in dire need of service. Left outside of your space station, there are chances you couldn't fire that thing at all, due to evaporation fo lubricants. And if you could, then it would probably jam before emptying single magazine. Of course all above assuming that it wasn't in the shade and therefore didn't froze solid or wasn't exposed to direct sunlight and therefore propellant didn't cooked in the bullets.

Baldwin
01-30-2008, 07:26 AM
I guess you could modify an existing firearm, or design one especially, to operate well in a vacuum. If anybody would do that, it'd be the Soviets; any chance that ever happened?

puppygod
01-30-2008, 08:42 AM
I guess you could modify an existing firearm, or design one especially, to operate well in a vacuum. If anybody would do that, it'd be the Soviets; any chance that ever happened?

I don't think so. Actually, I just realized that there ARE weapons, that most probably would work without problems in space. Underwater weapons like German HK P-11 (http://world.guns.ru/handguns/hg209-e.htm) or Russian SPP-1 (http://world.guns.ru/handguns/hg140-e.htm) would avoid most issues described in article and this thread. Little to no moving parts. Self-contained. In case of P-11 no barrel to overheat... And as a plus, elongated arrow-shaped projectiles would be great in piercing those spacesuits :cool:

Bricker
01-30-2008, 01:53 PM
I don't think so. Actually, I just realized that there ARE weapons, that most probably would work without problems in space. Underwater weapons like German HK P-11 (http://world.guns.ru/handguns/hg209-e.htm) or Russian SPP-1 (http://world.guns.ru/handguns/hg140-e.htm) would avoid most issues described in article and this thread. Little to no moving parts. Self-contained. In case of P-11 no barrel to overheat... And as a plus, elongated arrow-shaped projectiles would be great in piercing those spacesuits :cool:

Interestingly enough, both are discussed in my previous report on firing under water, found here (http://www.straightdope.com/mailbag/mgununderwater.htm).

yheffen
01-30-2008, 03:13 PM
...the Earth itself is an object in space at thermal equilibrium.

Uhhh... Wha? Being a lifelong inhabitant of Earth, specifically, its surface, I can report that it is not at thermal equilibrium with its environment. I've seen many examples of this state of non-equilibrium, but one particular example has to do with this rotation on an axis thing it does. At a particular point on the surface, say, where I am right now, it tends to be pretty warm at this point of rotation when the nearby star is blasting the surface with radiation. Things will continue to warm even as the angle of incidence of the radiation decreases until it starts to get pretty weak and the light gives way to the interstellar darkness. The temperature then starts to drop and pretty much continues to drop until the planet comes around so that the light starts hitting the surface again.

The temperature is pretty much changing the whole time during the diurnal cycle. That even neglects other local effects that show things are not at equilibrium like the fact an exposed object will be warmer or colder than this or that one due to differing rates of radiative heating and cooling, and neither object necessarily is the same temperature as the air, which is still different than that nearby body of water. Then we have larger scale thermal phenomena like pretty much all atmospheric meteorological phenomena, ocean currents, etc. that are driven by thermal gradients.

Oh, and then there is the facts that the Earth itself is a net thermal source due to radioactive decay beneath the surface and is still cooling from its formation.

Doesn't seem like equilibrium to me.

John W. Kennedy
01-30-2008, 03:23 PM
Well, first of all, there are a lot of various .22 - apart from .22 LR, there is .22 short and .22 WMR and some others, less popular. There is also .17 HMR. Compared to uber-popular .22 LR all other are rare, but they do exist.I'm more familiar with antiques, and even my "modern" knowledge is ca. 1960 or so, but that corresponds with what I know. Wikipedia lists very few rimfire cartridges that are not .17 or .22, and I believe they are all obsolete, most of them from the mid-19th century, when rimfire and centerfire were seen as rival, rather than complementary, technologies. Both .17 and .22 also have centerfire versions.

Chronos
01-30-2008, 03:43 PM
If you're going to talk about "the temperature of the Earth", you have to average over the entire surface, half of which is lit and half dark at any given time. So the diurnal or seasonal cycles don't change anything. The changing distance from the Sun would have an effect, but it's a relatively small one, as is the internal heating from radioactive decay. And the residual heat of formation was lost long ago.

puppygod
01-30-2008, 09:35 PM
Interestingly enough, both are discussed in my previous report on firing under water, found here (http://www.straightdope.com/mailbag/mgununderwater.htm).

You might be interested in "underwater Kalashnikov", APS (http://world.guns.ru/assault/as69-e.htm). There is another one underwater rifle, even more interesting (or crazy) because it's capable of firing either special underwater ammo with long projectiles, or standard 5.45 mm Russian ammo. ASM-DT (http://en.wikipedia.org/wiki/ASM-DT_Underwater_Assault_Rifle) is really fascinating piece of engineering, with magazine slot that can be adjusted to accommodate different magazines.

yheffen
01-31-2008, 02:17 AM
If you're going to talk about "the temperature of the Earth", you have to average over the entire surface, half of which is lit and half dark at any given time. So the diurnal or seasonal cycles don't change anything. The changing distance from the Sun would have an effect, but it's a relatively small one, as is the internal heating from radioactive decay. And the residual heat of formation was lost long ago.

Well, some sources I've seen say the residual heat from formation is still about 5 to 10% of the heat. So it's a small, but significant contribution. Hmmm... Here's a reference from a fairly reliable pop-sci source,

http://www.physorg.com/news62952904.html

But that is beside the point, your original message said,

An object in Earth orbit or the vicinity (which includes the Moon, the furthest from Earth humans have ever been) will have an equilibrium temperature in the vicinity of the temperatures you find on the Earth. This should be no great surprise, since the Earth itself is an object in space at thermal equilibrium.

The point I was trying to get to, but I guess I did not get across well is that due to the diurnal cycle of the Earth, temperatures on Earth really do not get to the equilibrium temperature that an objects in near-Earth space get when either exposed to or shielded from direct sunlight for long periods. Terrestrial temperatures are moderated by the heat capacities of the great masses of the land, air, and water. The temperature of the Earth rises all day until the sun starts to get pretty low which tells you we never reached equilibrium. An object in space that is exposed to the direct sun for a much greater time and does reach reach equilibrium could get a lot hotter. The reverse is true for night. The temperature drops all night. We never get down to the equilibrium temperature that an object near Earth that spent an extended period of time in shadow would get to. (Or an object with less mass and therefore less heat capacity gets to equilibrium more quickly.)

For example, the moon, which rotates with respect to the sun every 28 days and has no atmosphere, has more time for a given point to get into equilibrium with the sky and less ability to transport heat via bulk mass transport. The moon has surface temperature variations between about -230 to 120 C between night and day. So, I personally would not call that range "the vicinity of of the temperatures you find on Earth" given that the cold and hot records on Earth are in the -90 and 57 C neighborhood, respectively.

Finally, we've been completely abusing the word equilibrium. What I've called equilibrium above is not really equilibrium, but steady state. Yes, the temperature of the test object will not change with time, but it is not at true thermal equilibrium with its surroundings.

puppygod
01-31-2008, 04:15 AM
(...)
Finally, we've been completely abusing the word equilibrium. What I've called equilibrium above is not really equilibrium, but steady state. Yes, the temperature of the test object will not change with time, but it is not at true thermal equilibrium with its surroundings.

Man, I love this board. Where else posters would be self-nitpicking?

Baldwin
01-31-2008, 09:14 AM
I'd just like to note that it was 50 years ago today (Januay 31, 1958) that the U.S. entered the Space Age by launching Explorer 1 into orbit, the first artificial satellite in the history of Mankind, except for the two launched some months earlier by the Commies.

OtakuLoki
01-31-2008, 09:20 AM
<snickering>

scr4
01-31-2008, 10:24 AM
The point I was trying to get to, but I guess I did not get across well is that due to the diurnal cycle of the Earth, temperatures on Earth really do not get to the equilibrium temperature that an objects in near-Earth space get when either exposed to or shielded from direct sunlight for long periods.
I think Chronos's point was that the Earth as a whole is in thermal equilibrium with its surroundings. The amount of heat received (and generated, as you pointed out), minus the amount of heat lost by radiation, is close to zero. It's not exactly zero as the rate of heat received/absorbed is not constant, but it's pretty close to it and doesn't underscore the point Chronos was trying to make.

What I've called equilibrium above is not really equilibrium, but steady state.
If you take the environment (sun, stars, background radiation, etc) as a given, then wouldn't it be valid to say the earth is in thermal equilibrium with it?

Chronos
01-31-2008, 01:20 PM
The temperature of the Earth rises all day until the sun starts to get pretty low which tells you we never reached equilibrium.The temperature of any given part of the Earth rises in the day and drops at night, but the Sun never sets on the Earth as a whole. It's always lunchtime somewhere on the globe, and likewise always sunset, always midnight, always brillig, and so on.

tychof
02-01-2008, 06:52 AM
IANAPhysicist, so take this with some cautions.

After the box radiated off it's excess energy, from being placed there, it would eventually come to equilibrium at what is sometimes called "the temperature" of space.

http://www.aerospaceweb.org/question/atmosphere/q0291.shtml

"even though space is generally very cold, the fact that it is a vacuum means there is no medium to conduct heat away from the body"

The box is not going to 'radiate' excess energy, unless it's actually spewing material of some sort. In fact, my guess is that the box would heat up if it's relatively near a star.

Which implies that a big problem with guns in space is that you can fire fewer times, as barrel would heat up faster than on Earth causing all kinds of damage.

OtakuLoki
02-01-2008, 07:45 AM
http://www.aerospaceweb.org/question/atmosphere/q0291.shtml

"even though space is generally very cold, the fact that it is a vacuum means there is no medium to conduct heat away from the body"

The box is not going to 'radiate' excess energy, unless it's actually spewing material of some sort. In fact, my guess is that the box would heat up if it's relatively near a star.

Which implies that a big problem with guns in space is that you can fire fewer times, as barrel would heat up faster than on Earth causing all kinds of damage.

Your implications are all right - but remember heat radiation, or black body radiation (http://en.wikipedia.org/wiki/Blackbody_radiation), happens as a result of the temperature of the material.

The last clause in the sentence you quoted is pretty important: "...and it cools rather slowly."

It doesn't need a medium for heat exchange, because it's radiating in the infrared. In a vacuum it's a slow process. And in sunlight, it would be negligible, compared to the heat input from the sun's radiation - which includes it's own black body radiation.

Which, as I say, doesn't invalidate all your conclusions. Just a small error in your premises.

Oh, I forgot to thank SlowMindThinking for the correction of my own errors.

QUAKEBOT
02-01-2008, 12:32 PM
This post should be called: Would gunpowder burn in outer space. Then I wouldn't have to read all the crud that is posted about temperature and recoil- who cares.

At outer space temperature extremes the steel and or plastic a conventional firearm is constructed of would not hold up to even one discharged round. So arguments about how a gun works and recoil are completely senseless.

The spring steel in the firing mechanism would not work either. If you did manage to explode a round in the chamber your space suit would be compromised by throusands of small shards of brass, plastic and steel a split second after the entire firearm burst. Unless you are using a special "space gun".

Maybe someone can figure out how long it will take for the shards of metal to hit the visor of someone who has A7L suit on and stands 6 feet tall.

scr4
02-01-2008, 01:32 PM
This post should be called: Would gunpowder burn in outer space.
I agree that's the only part of the question answered by this article, but that doesn't mean we should continue to ignore other issues.

At outer space temperature extremes the steel and or plastic a conventional firearm is constructed of would not hold up to even one discharged round
As already explained, an object near earth and in sunlight would reach a reasonable temperature (close to the average temperature on earth). It would take longer to cool down after each shot, as heat is only carried away by radiation, but that shouldn't affect the first shot.

The spring steel in the firing mechanism would not work either.
Why not?

puppygod
02-01-2008, 01:34 PM
(...)
At outer space temperature extremes the steel and or plastic a conventional firearm is constructed of would not hold up to even one discharged round. So arguments about how a gun works and recoil are completely senseless.

The spring steel in the firing mechanism would not work either. If you did manage to explode a round in the chamber your space suit would be compromised by throusands of small shards of brass, plastic and steel a split second after the entire firearm burst. Unless you are using a special "space gun".
(...)

And you base your assertion on what? I mean we all know that steel at temperatures close to absolute zero is to brittle, but hey, what's unreasonable in scenario like that:

You put your space shuttle on orbit along rogue satellite. Put your spacesuit, takes your trusty Colt .45 and heads to airlock. Open it, climb outside, aim at nearby satellite and pull the trigger. Since loss of temperature due to radiation will be very little, all parts of gun would still be close to 20 Celsius or whatever is standard temperature inside space shuttle. Why shouldn't your pistol fire as usual?

Stranger On A Train
02-01-2008, 03:17 PM
This post should be called: Would gunpowder burn in outer space. Then I wouldn't have to read all the crud that is posted about temperature and recoil- who cares.You're not going to like it here much, then. This sort of grist is just what the mill of this board feeds upon.

At outer space temperature extremes the steel and or plastic a conventional firearm is constructed of would not hold up to even one discharged round. So arguments about how a gun works and recoil are completely senseless.

The spring steel in the firing mechanism would not work either. If you did manage to explode a round in the chamber your space suit would be compromised by throusands of small shards of brass, plastic and steel a split second after the entire firearm burst. Unless you are using a special "space gun".As an engineer who works on rockets and space systems, I can assure you that this is not the case. It is true that many steels will become brittle in exposure to cold, but it is hardly the case that they would shatter into "thousands of small shards of brass, plastic, and steel" or that "the entire firearm [would] burst." If thermal fracture did occur due to temperature (most likely at a weld or geometric stress concentration like a small radius fillet) then it would just brittle fracture as materials here on Earth do, rather than exploding in the fantastic manner described. Most steels used for high quality springs are quite resistant to thermal stress fracture as a result of being carefully alloyed and tempered to survive an "infinite" stress life. (Infinite being longer than the anticipated life of the machine they are a part of.) Of course, springs do break or wear out occasionally, but when was the last time you went in for a routine replacement of your valve springs on your car engine?

One does have to select materials carefully for use in space environments, and the thermal stress cycling between sunlight and shadow could potentially cause premature fatigue, or interferences between aluminum and steel components which will expand at different rates. Long term exposure to space environments would cause volatiles in polymer frames and components to sublimate, and the harsh UV would eventually start to break down polymer chains (though the glass fiber used in most polymer composite gun frames would retain its form indefinitely), but the most likely problems in firing a conventional firearm in space are evaporation of lubricants (already mentioned) and possibly issues with ambient pressure on gas piston-operated arms (though I suspect this would be minimal). The lubricant problem could be addressed by using dry lubricants that are resistant to vacuum adhesion, and in fact, a version of Dri-Slide--advocated by some gun owners for tight tolerance firearms that are prone to contamination faults--is actually used for lubricating mechanisms on satellites and spacecraft.

If you were going to carry a weapon in vacuum for long term (perhaps to protect yourself against buzzing monoliths and psychotic spacecraft computers) then you'd want to design it to withstand the hazards of that environment. If you just want to pop outside your Shuttle for a quick gunfight with a passing megalomaniac or antagonistic cosmonaut, however, the trusty old 1911 will probably serve you quite well. Just rememeber, in space, it is always "high noon".

Stranger

Santo Rugger
02-01-2008, 11:00 PM

Yes. Anything that's deflagrating or detonating combusts too fast for it to get its required oxygen from the air, so it must carry its own. Oxygen balance describes the percentage of oxygen available compared to the amount of oxygen necessary for complete combustion, with respect to molecular mass.

Quercus
02-05-2008, 04:01 PM

Yes. Anything that's deflagrating or detonating combusts too fast for it to get its required oxygen from the air, so it must carry its own. Oxygen balance describes the percentage of oxygen available compared to the amount of oxygen necessary for complete combustion, with respect to molecular mass.Well, I agree in general: any compact thing that detonates is supplying its own oxidizer. And any kind of gunpowder falls into this category.

But you can get real explosions using atmospheric oxygen; you just have to suspend the fuel, either as a gas or in particles or droplets. Examples include a natural gas explosion, grain elevator explosions and fuel-air bombs. They all need just the right balance of fuel and air, but do happen.

Allston
02-10-2008, 09:00 PM
Interesting discussion (thanks for mentioning it, "Clicker").

No, a firearm will *not* work in space, despite confident commentary. Although it *will* propel the round (as well as affecting you - Newton's Third Law), it would be a very tepid end-velocity.

The reason is that your propellant was not formulated to contain it's own oxidizer (except by chance), given it was intended to be used within our atmosphere (e.g. the source of a readily available oxidizer). Simply, the total amount of actual oxidizing elements contained will be minimal. This is a chemical fact. :smack:

The round will indeed be propelled, but a a low velocity, compared to the same attempted event on the surface of the planet. Flick a pea at someone, and you have a good mental image of the carnage you won't commit.

If you want to insist that you are actually firing a firearm, given the tiny end-velocity, please do. However, you are talking the difference between firing an arrow from a longbow, and just weakly throwing the arrow at it's target by hand (a suspect analogy, but go with it for the moment).

So. Formulate a new propellant that contains a significant proportion of it's own oxidizer, and yes, your firearm will work as desired :D ; use our current standard propellants, and you will get a tiny pop. :(

Stranger On A Train
02-10-2008, 09:19 PM
No, a firearm will *not* work in space, despite confident commentary. Although it *will* propel the round (as well as affecting you - Newton's Third Law), it would be a very tepid end-velocity.

The reason is that your propellant was not formulated to contain it's own oxidizer (except by chance), given it was intended to be used within our atmosphere (e.g. the source of a readily available oxidizer). Simply, the total amount of actual oxidizing elements contained will be minimal. This is a chemical fact. :smack:No, that is a chemical falsity. Gunpowder and modern smokeless powders have all the oxidizer they need in the form of nitrates (most commonly potassium nitrate) which is mixed in with the propellant. If this were not the case, there is no way that the powders would burn forcefully enough to expell a projectile at several hundred feet per second, nor is the amount of oxygen found in the cartridge sufficient to provide complete combustion.

Stranger

Allston
02-10-2008, 09:42 PM
Where does an equivalent amount of oxidizers magically appeared in this chemical process to replace that which is no longer present (absence of atmosphere)?

TANSTAAFL, Bud. :)

[ A+15 - 15 does NOT equal A+15 ]

Allston
02-10-2008, 09:55 PM
"Appear," not "Appeared," rather.

[Edtngi Sklils week tongith]

Allston
02-10-2008, 10:19 PM
After a bit of thought, one further post (then I'll shut the hell up!):

Modern propellants are designed to have a specific burn rate within atmosphere (performance X, between Y bars and Z bars of atmospheric pressure). With no atmosphere, your burn is very different, and unless you're postulating the chamber of a firearm is a totally sealed environment, you will experience a large gas loss. Most propellants are approximately 20% oxidizer, but taken as with any equation, the presence of atmosphere is a distinct part of it. It may even be opaque to most, e.g. not mentioned, but it's there nonetheless. In short, a huge decrease in gas-pressure by which to propel your round.

[Different skew if this is not an automatic, of course]

Stranger On A Train
02-11-2008, 12:40 AM
Where does an equivalent amount of oxidizers magically appeared in this chemical process to replace that which is no longer present (absence of atmosphere)?

TANSTAAFL, Bud. :)There is no magical appearance of oxidizers needed. The simple formula for the combustion of black powder (comprised of saltpeter, sulphur, and charcoal) for instance:2KNO3 + S + 3C => K2S + 3CO2 + N2
requires no atmospheric oxidizers. (The actual products are more complex due to incomplete combustion and side products, but this has nothing to do with atmosphere or lack thereof.) The grain size of black powder and smokeless powders (http://en.wikipedia.org/wiki/Image:N110_ruuti.jpg) is insufficiently small--and deliberately so, lest handling the powder in bulk result in a hazardous atmosphere--to allow rapid combustion at surface using atmospheric oxygen. Taking an equivilent amount of charcoal ground to the same grain size would result in an aggregate that might burn aggressively at STP but wouldn't serve as an adequate propellant for a firearm. In order to get effective combustion using atmospheric oxygen requires a much finer grain size and a concentration that is roughly stoichiometric to atmospheric oxygen, as occasionally seen in silo or coal mine explosions.

The oxidizer for a solid propellant--the oxygen-bearing nitrate--functions as the oxidizer for this reaction. See Cooper's Explosives Engineering (http://www.amazon.com/Explosives-Engineering-Paul-W-Cooper/dp/0471186368), Chapter 2, for more details on oxidation reactions in combustion and detonation and oxidizer balance.

Stranger

Elendil's Heir
02-12-2008, 08:12 AM
Smart people arguing arcane topics and even getting a little testy - just one more reason I love the Dope!

Baldwin
02-12-2008, 08:18 AM
After a bit of thought, one further post (then I'll shut the hell up!):

Modern propellants are designed to have a specific burn rate within atmosphere (performance X, between Y bars and Z bars of atmospheric pressure). With no atmosphere, your burn is very different, and unless you're postulating the chamber of a firearm is a totally sealed environment, you will experience a large gas loss. Most propellants are approximately 20% oxidizer, but taken as with any equation, the presence of atmosphere is a distinct part of it. It may even be opaque to most, e.g. not mentioned, but it's there nonetheless. In short, a huge decrease in gas-pressure by which to propel your round.

[Different skew if this is not an automatic, of course]Stranger on a Train handled the chemical part of contradicting you. On the physics side -- the difference between ground-level atmospheric pressure and a vacuum is only 15 psi. Surely that's a small fraction of the gas pressure created by the combustion of a round's propellant. It's hard to believe that a significantly greater amount of gas will leak out ahead of the bullet (I presume that's what you're talking about) in orbit than on the ground. If anything, since most of the gas will stay behind the bullet until it's expelled from the barrel, the lack of an outside atmosphere should allow for more rapid acceleration (in the barrel) and a higher velocity for the ballistic projectile (after it's left the barrel) than when you're shooting in your backyard.

Bricker
02-12-2008, 09:23 AM
Stranger on a Train handled the chemical part of contradicting you. On the physics side -- the difference between ground-level atmospheric pressure and a vacuum is only 15 psi. Surely that's a small fraction of the gas pressure created by the combustion of a round's propellant. It's hard to believe that a significantly greater amount of gas will leak out ahead of the bullet (I presume that's what you're talking about) in orbit than on the ground. If anything, since most of the gas will stay behind the bullet until it's expelled from the barrel, the lack of an outside atmosphere should allow for more rapid acceleration (in the barrel) and a higher velocity for the ballistic projectile (after it's left the barrel) than when you're shooting in your backyard.

Correct. As the wise, handsome, and eloquent author of this article (http://www.straightdope.com/mailbag/msilencer.htm) suggests, the internal gas pressure involved exceeds 3,000 PSI. It's not particularly relevant for this series of events if the external pressure is 15 PSI or 0 PSI, since the difference would change from 2,985 PSI to 3,000 PSI - a negligible shift.

Lemur866
02-12-2008, 11:33 AM
As Stranger explains, explosives are different than combustibles. An explosive has to contain its own oxidizer, otherwise it won't explode, it will burn.

This is why gasoline can't be used as propellant in a gun. It will burn, but it won't explode unless it is carefully mixed with air first.

EdIsenberg
08-12-2011, 02:17 PM
I agree that's the only part of the question answered by this article, but that doesn't mean we should continue to ignore other issues.

As already explained, an object near earth and in sunlight would reach a reasonable temperature (close to the average temperature on earth). It would take longer to cool down after each shot, as heat is only carried away by radiation, but that shouldn't affect the first shot.

Why not?

1) I believe the question that was asked was "would a gun work in space." Whether the bullet fires is a subset question. If it is false, that ends the original thread. If it is true that bullets work in space, that still doesn't answer the asked question. So, in short, I do not agree with you that this topic subject should be changed just because one or more people want to focus on a subset issue.

2) <<an object near earth and in sunlight would reach a reasonable temperature (close to the average temperature on earth)>>

This is incorrect. The Moon is near Earth, and its temperature during the day on its equator is 390 degrees Kelvin, or 242 degrees F. There are several reasons why the Earth is cooler in the full light of the Sun than an object like The Moon or on a geostationary orbit as satellite TVs. (sources: www.Wikipedia.com and www.convert-me.com/en/convert/temperature).

a) The Earth radiates much of the Sun's energy by reflection off clouds. I don't know how much of the surface is covered in clouds but if you look at any photo of our planet you'll notice it is substantially covered in clouds.

b) At the poles, the arctic and antarctic are covered in ice and snow, which further reflect light into space, albeit not efficiently.

c) One of the biggest reasons is that we have a dense atmosphere. Surface winds, convection, and especially the jet stream distribute the heat from the sunlit side to the night side. Without this the night side would be too cold to survive.

d) Another big reason is that 70% of the world is covered by water. The solar energy water receives is dissipated by many ways. Some of the energy warms the water below the surface through convection and conduction. Thermohaline circulation (THC) (of which the Gulf Stream is an example) distribute water from the hot equator towards higher latitudes. That's why northern Europe, European Russia and especially Ireland and Great Britain aren't much colder. As the circulation becomes colder and saltier, it sinks and then continues in a southerly direction, until it picks up heat near the equator. This is the world-wide current driven by the Sun's energy.

There are probably other reasons I'm just not thinking of right now, but hopefully you get the idea. Anything in airless space in view of the Sun gets very hot, and anything in shadow cools down to well below freezing. The reason the Space Shuttle used to fly with its cargo bay doors open and facing the Earth was to help dissipate heat. The reason space suits and other technology in space are uniformly white is to reflect heat rather than absorb it.

Source: http://en.wikipedia.org/wiki/Thermohaline_circulation

Ed Isenberg

qazwart
08-12-2011, 02:32 PM
There was an episode of Firefly where Jayne fires his favorite gun, Vera, at another spaceship just outside of his spaceship. They wrapped the gun in a spacesuit, so it would have the oxygen it needed in order to fire.

I guess the creators of the show didn't realize that guns don't need free oxygen to fire, or they simply decided that most people wouldn't know that and this would keep down the complaints.

Chronos
08-12-2011, 02:38 PM
2) <<an object near earth and in sunlight would reach a reasonable temperature (close to the average temperature on earth)>>

This is incorrect. The Moon is near Earth, and its temperature during the day on its equator is 390 degrees Kelvin, or 242 degrees F.And nighttime temperatures on the Moon are much colder than Earthly temperatures. The average, though, is still about the same. And heat transport around the surface of the Earth is negligible compared to the heat that a spot has from being in sunlight just a few hours earlier-- Even the jet stream doesn't blow at 1000 miles per hour. The Moon's temperature would be a lot more stable if it rotated rapidly like the Earth.

EDIT:There was an episode of Firefly where Jayne fires his favorite gun, Vera, at another spaceship just outside of his spaceship. They wrapped the gun in a spacesuit, so it would have the oxygen it needed in order to fire.

I guess the creators of the show didn't realize that guns don't need free oxygen to fire, or they simply decided that most people wouldn't know that and this would keep down the complaints. Or the creators of the show did know, but figured that Jayne wouldn't, and so had him taking the precaution without realizing that it was unnecessary.

EdIsenberg
08-12-2011, 08:41 PM
And nighttime temperatures on the Moon are much colder than Earthly temperatures. The average, though, is still about the same. And heat transport around the surface of the Earth is negligible compared to the heat that a spot has from being in sunlight just a few hours earlier-- Even the jet stream doesn't blow at 1000 miles per hour. The Moon's temperature would be a lot more stable if it rotated rapidly like the Earth.

First, you are still incorrect. The average temperature on The Moon at its equator is 220K or minus 64 degrees F.

Second, heat transport around the surface of the Earth (and to lower levels of the oceans) is not insignificant. To the contrary, the atmosphere, its components (e.g., carbon dioxide and methane gas) and oceans are the major mitigating forces behind our climate.

Third, the Moon's temperature would not be more stable if it rotated rapidly like the Earth. The reason is that conduction of the lunar surface w/o convection to help doesn't work well at all.

I don't know where you learned either of these three statements.

Nowhere on Earth does the temperature make swings from 390 K (242 F) during the day to 100 K (-280 F) at night. The reason why is that between our huge oceans and thick atmosphere the Sun has to heat far more than a surface in view of the Sun in outer space. the deep oceans and our atmosphere both act as heat sinks.

www.wikipedia.com is my major source. If you have information to the contrary what is its source, how credible is it compared to wikipedia, and how does it account for the relatively stable temperatures from day to night on Earth's surface as opposed to The Moon or any object (e.g., Shuttle, EVA suits, satellites, International Space Station) roughly one Astronomical Unit from the Sun?

We've gotten a bit far from the topic of the practicality of using a gun in outer space, but I didn't want to read all the messages after yours until we had settled the issues you raised.

BTW, I am an amateur astronomer with about \$5,000 in telescopes, cameras etc., I was for two years President of an Astronomical Society. I've given more speeches on the subject of astronomy that I care to remember. All of them were first researched on reputable web-sites. Oh, and on Tuesday I give a major presentation to Southwest Writers (500 members in New Mexico) on Research for Writers.

Ed Isenberg

ZenBeam
08-13-2011, 10:11 AM
From NASA's website, they have an estimate for the temperature (http://www.grc.nasa.gov/WWW/k-12/Numbers/Math/Mathematical_Thinking/estimating_the_temperature.htm) of a flat black plate in space:
Thus, the nominal temperature of an object, in space and in sunlight, is 394 °K.(You can ignore the particle flux energy most of that link is concerned with. At the end, he determines that it's negligible.)

If I'm reading that correctly, that assumes the radiating area is the same as the area receiving sunlight. So it would be correct for a flat plate facing the Sun, with an insulated back side.

Since radiation goes as T^4, if both sides of the plate could radiate, the temperature would be smaller by (1/2)^(1/4) = 0.84, or 331 °K, or 136 °F. For a sphere (small enough to have a roughly uniform temperature), the radiating area would be four times the area receiving solar radiation, and the temperature would be smaller by (1/4)^(1/4) = 0.707, or 279 °K or 43 °F. For those last two temperatures, the radiation from the Earth should also be included, so they'd be somewhat higher.

A gun won't be a true black body, and also is neither a flat plate nor a sphere, so there's some large error bounds, but until someone models an actual gun, using it's actual absorption and emissivity, and for a range of orientations, assuming the gun will be somewhere in the range of 40 to 140 °F seems the best we can do.

I'd expect a gun to operate over that range of temperatures.

penumbrage
08-13-2011, 10:31 AM
There was an episode of Firefly where Jayne fires his favorite gun, Vera, at another spaceship just outside of his spaceship. They wrapped the gun in a spacesuit, so it would have the oxygen it needed in order to fire.

I guess the creators of the show didn't realize that guns don't need free oxygen to fire, or they simply decided that most people wouldn't know that and this would keep down the complaints.

Not just Jayne's favorite gun but his most prized single possession. Maybe he just didn't want Vera suffering the aforementioned mechanical abuse and degradation.

The whole thread is just a physics exercise anyway, true space cowboys pack Gyrojets.
http://en.wikipedia.org/wiki/Gyrojet

EdIsenberg
08-13-2011, 03:56 PM
From NASA's website, they have an estimate for the temperature (http://www.grc.nasa.gov/WWW/k-12/Numbers/Math/Mathematical_Thinking/estimating_the_temperature.htm) of a flat black plate in space:

Since radiation goes as T^4, if both sides of the plate could radiate, the temperature would be smaller by (1/2)^(1/4) = 0.84, or 331 °K, or 136 °F.

Your conversion of Kelvin (°K) to °F in incorrect. You can find the correct conversion by going to http://www.convert-me.com/en/convert/temperature which shows the true temperature is not 136 °F but 249 °F. This is in complete agreement with the maximum temperature on The Moon's equator of 390 °K or 242.3 °F. Actually, I was surprised at the similar numbers, since The Moon is not a "black body" but has many different colors, including shades of white (in mountainous terrain). I don't know what contribution energy reflecting off the mountains back down to nearby flat surfaces, but given the light color of those nearby surfaces I wouldn't expect it to be significant.

A gun won't be a true black body, and also is neither a flat plate nor a sphere, so there's some large error bounds, but until someone models an actual gun, using it's actual absorption and emissivity, and for a range of orientations, assuming the gun will be somewhere in the range of 40 to 140 °F seems the best we can do.

I'd expect a gun to operate over that range of temperatures.

Whether a gun would fire even once, never mind multiple times, is more complicated, and the effectiveness of the gun is still more complicated.

Would a gun work in outer space? Sometimes yes, sometimes no, and sometimes it will explode on you, ruining your whole day. Don't ask what would happen to an astronaut with a dozen holes in his/her space suit and, under that, a dozen holes in his/her body. It is very grisly.

The problem is because a gun may be white or black, may be in sunlight or shadow, and the bullet (not the casing) is inside the gun, and may be made of a lead/tin alloy or jacketed coated lead. The shell (casing) can be made of lead, copper, brass, steel, or other materials including combinations of the above. This variety means it is hard to predict which is more affected by heat, the bullet, the casing, or the gun barrel. Guns and ammunition are made so that upon firing the bullet will eject from the casing and then the muzzle. If the bullet expands by heat but the gun barrel doesn't, you could easily have an explosion in the chamber where the bullet sits (see above). Or it may work perfectly. It is impossible to generalize.

Whether guns can be fired accurately or repeatedly is another issue, depending on physics. Most fully-automatic "assault rifles" or machine guns have three settings: single shot, 3-shot, and continuous fire. The reason is that after 3 shots are fired on Earth, your gun will rotate and lift in your hands, making additional shots on automatic completely uncontrollable. "Continuous" is only used for "covering file" while another person tries to advance toward the target. It keeps the target's head down. Now, that's on Earth with Earth's gravity. If you are on The Moon, with only one-sixth Earth gravity, firing two shots in quick succession will result in the second shot going wild.

In zero or microgravity (not the same) or even on a low-gravity environment like The Moon, the recoil from a gun aimed by sight will make the shooter tumble backwards head-over heels. It will also apply some thrust to the shooter, so that he/she will be thrust backward in space. There is no easy recovery when this happens, and when multiple shots are fired from the eye of the shooter, the tumbling can cause all the blood to run to his/her feet, making the shooter pass out and even die of oxygen-starvation to the brain. The impact of the gun hitting the shooter's helmet might even leave a serious crack, so that the shooter dies both from decompression and oxygen-starvation.

In summary, unmodified earth guns, rifles and shotguns may work, might not work, or might explode. Firing a single shot in low or zero gravity can also be very dangerous to the shooter, never mind making further shots go completely wild. For these reasons, the answer to "Would a gun work in space" is unpredictable but certainly dangerous to the shooter.

I call that answer a qualified "No."

Ed Isenberg
amateur astronomer
soon to be a published science fiction novelist.

Chronos
08-13-2011, 04:09 PM
Second, heat transport around the surface of the Earth (and to lower levels of the oceans) is not insignificant. To the contrary, the atmosphere, its components (e.g., carbon dioxide and methane gas) and oceans are the major mitigating forces behind our climate.
Compared to the Earth's rotation, it is. Heat transfer via air or water currents from the light side of the Earth to the dark side could only occur as fast as the speed of the current. The jet stream tops out at around 400 km/h, and is usually only a quarter of that. The Earth's rotation at those latitudes, meanwhile, is well over 1000 km/hr. So by the time heat could reach the dark side from the light side, the dark side would itself be the light side.

The atmosphere does have a significant effect on the average temperature, via the greenhouse effect on one hand, and reflective clouds on the other. But it does not have a significant effect on keeping the planet's temperature uniform from day to night.

And any gun at risk of exploding in space would also be at risk of exploding on Earth.

ZenBeam
08-13-2011, 04:52 PM
Your conversion of Kelvin (°K) to °F in incorrect. You can find the correct conversion by going to http://www.convert-me.com/en/convert/temperature which shows the true temperature is not 136 °F but 249 °F. This is in complete agreement with the maximum temperature on The Moon's equator of 390 °K or 242.3 °F. Actually, I was surprised at the similar numbers, since The Moon is not a "black body" but has many different colors, including shades of white (in mountainous terrain). I don't know what contribution energy reflecting off the mountains back down to nearby flat surfaces, but given the light color of those nearby surfaces I wouldn't expect it to be significant.According to your link, my conversions are correct. 331 Kelvin is 136.1 Fahrenheit, as I had written.

Also, please drop the red text.

ZenBeam
08-13-2011, 05:00 PM
The atmosphere does have a significant effect on the average temperature, via the greenhouse effect on one hand, and reflective clouds on the other. But it does not have a significant effect on keeping the planet's temperature uniform from day to night.I don't believe the bolded statement is correct. Clouds and humidity tend to hold in the Earth's heat overnight. Clear, dry nights allow more heat to escape.

EdIsenberg
08-13-2011, 05:25 PM
[QUOTE=Chronos
And any gun at risk of exploding in space would also be at risk of exploding on Earth.[/QUOTE]

I won't keep repeating myself for your entire response, because you make statements without any citation, and without responding with why you feel my remarks are incorrect. I do want to point out your statement quoted above.

The reason a gun can explode in outer space or on The Moon is due to different expansion and contraction of the bullet, the cartridge casing, and the barrel of the gun. Since on Earth we don't have such a different temperature between sunlight and shadow (or day and night), the expansion & contraction doesn't have much effect, and are well within the tolerances of the gun and ammunition specifications.

Ed Isenberg

EdIsenberg
08-13-2011, 05:34 PM
According to your link, my conversions are correct. 331 Kelvin is 136.1 Fahrenheit, as I had written.

You are correct if the temperature is 331 Kelvin. However, referring back to the excellent site on NASA (http://www.grc.nasa.gov/WWW/k-12/Numbers/Math/Mathematical_Thinking/estimating_the_temperature.htm), the predicted equilibrium temperature of a black body in full sunlight and in outer space is not 331 but 394 K, which is indeed 249.5 F.

The exact wording of the NASA article includes the following.
The balance between incoming energy and outgoing (radiated) energy causes the plate to come to an equilibrium temperature. The problem is to calculate this temperature.

We begin with Stefan-Boltzmann's law for a black body in sunlight.
SSUN = sigma T4 W/m2

This law enables us to estimate the temperature T of such an object, assuming that we know the power per unit area SSUN falling on the plate. From direct measurement, we know that at 1 A.U,
SSUN = 1,360 W/m2.

We also know that
sigma = 5.67 x 10-8 W/(m2 K4).

Thus, the nominal temperature of an object, in space and in sunlight, is 394 °K.

ZenBeam
08-13-2011, 07:02 PM
OK, you didn't read or didn't understand my first post. I'll go over it again:

At the NASA site, the author calculated the temperature of a flat plate facing the Sun. He assumed that the area of that plate radiating as a black body was the same as the area capturing sunlight. Thus, in his calculation, only the top surface is radiating energy. Plates have two sides, and he has no contribution for energy radiating from the back side. This can be appropriate if he, for example, is calculating how hot the skin of a satellite will get on the side facing the Sun, with insulation between the skin and the inside of the satellite. For this case he gets a temperature of 394 °K. Call this T0.

For a thin flat plate, uniformly heated and able to radiate energy from both sides, if the plate were still 394 K, it would be radiating twice as much energy as it receives. Obviously this would not be correct. The temperature of the plate will be less, so that it only radiates the amount of energy it receives from the Sun. The energy from the Sun is the same, so each side needs to radiate half the energy. Call the temperature of the plate in this case T1. Since the energy radiated is proportional to T4, we have that 2*T14 = T04, or that T1 is only 331 °K.

Likewise for the sphere. Call its temperature T2. The cross-sectional area of a sphere is pi*r2, and the area of the surface of the sphere is 4*pi*r2. Since the surface area in this case is 4 times the cross-sectional area, we have that 4*T24 = T04, or that T2 is 279 °K.

Zeriel
08-13-2011, 07:34 PM
I won't keep repeating myself for your entire response, because you make statements without any citation, and without responding with why you feel my remarks are incorrect. I do want to point out your statement quoted above.

The reason a gun can explode in outer space or on The Moon is due to different expansion and contraction of the bullet, the cartridge casing, and the barrel of the gun. Since on Earth we don't have such a different temperature between sunlight and shadow (or day and night), the expansion & contraction doesn't have much effect, and are well within the tolerances of the gun and ammunition specifications.

I looked this up a bit:

Copper = 0.016mm/m per degK
416 Stainless = 0.010mm/m per degK
Various Lead Alloys = around 0.028mm/m per degK

So if there's going to be a problem, it'll be in the bullet itself. The worst problem that can happen with the casing is that the gun will jam or improperly feed, and in that case it won't explode anyway. So let's take a common military caliber: 5.56×45mm NATO

The Earth-nominal diameter for the bullet itself is 5.7mm (or 0.0057m) @68 degF (293 degK).
By your cite, the nominal black-body temperature of an object in space will end up at 394 degK--a difference of 101 degK. We'll use that number since it gives us the greatest temperature difference likely to be in play.
With that difference in temperature, you'd expect to see the bullet expand by 0.0057*101*0.028 = 0.000016m, or 0.016mm, an increase of 0.28%.
In the same heat, the barrel expands by 0.0057*101*0.010 = 0.0000057m, or 0.0057mm, an increase of 0.10%

The difference in the two diameter increases is 0.010mm

So the question then becomes, "Is a typical rifle capable of dealing with being 0.010mm out of tolerance without exploding?" I don't honestly know the answer to this question, and I can't find one in limited googling. Given, however, that I know people who routinely feed 5.56x45mm through .223 Remington rifles and vice-versa (the latter case makes me be very far away just in case they are unclear on the pressure differences from the powder loads, granted), I expect the answer to be "yes"--especially since the ANSI B4.1 tolerance grade 8 (the highest generally specified for "boring" operations like machining a rifle barrel) is 0.0177mm or thereabouts.

Now, if they're using diamond-drill boring for those gun barrels or a different process altogether, then we can talk, but right now I'm personally comfortable with "won't explode".

I'm also willing to bet that, given the relative speed of conduction in metal vs. radiation received in terms of transferring heat, the situation where part of a gun is in sunlight and part is in shadow is not especially relevant.

chorpler
08-13-2011, 08:45 PM
Don't ask what would happen to an astronaut with a dozen holes in his/her space suit and, under that, a dozen holes in his/her body. It is very grisly.

Please, tell us what would happen -- I'm interested to hear what your opinion on the subject is. From the research I've seen, it doesn't appear to be that grisly, but you may have different sources.

Chronos
08-13-2011, 09:01 PM
To be fair, an astronaut pumped full of holes would be considerably grislier than an astronaut exposed to vacuum without extra holes, or a person pumped full of holes in Earth-normal atmosphere.

chorpler
08-13-2011, 09:48 PM
Well my question isn't limited to EdIsenberg. Can you explain the details?

(I mean, assuming you're talking about something more grisly than just "there's extra blood coming out of the holes," which it sounds like you are since you specified that it would be more grisly than in an Earth-normal atmosphere.) Exposed fluids will boil in a vacuum, but I'm assuming there's more to making it grisly than just clouds of blood vapor.

In my experience, posters like Chronos and science fiction authors like EdIsenberg are usually pretty good at describing things like this and backing them up with cites, so I'm anxious to learn, even if it is somewhat disturbing.

Chronos
08-13-2011, 10:40 PM
You'd bleed out faster in vacuum than in atmosphere, and any blood that shot out would just keep on going out, in zero-g. And personally, I think that clouds of boiling blood would be plenty grisly enough, thank you very much.

chorpler
08-14-2011, 01:31 AM
You'd bleed out faster in vacuum than in atmosphere, and any blood that shot out would just keep on going out, in zero-g. And personally, I think that clouds of boiling blood would be plenty grisly enough, thank you very much.

Heh heh ... oh, sure, grisly enough, but compared to the effects in Outland or Total Recall, it's pretty tame ... and those people hadn't even been punched full of holes.

penumbrage
08-15-2011, 02:03 PM
After a bit of thought, one further post (then I'll shut the hell up!):

Modern propellants are designed to have a specific burn rate within atmosphere (performance X, between Y bars and Z bars of atmospheric pressure). With no atmosphere, your burn is very different, and unless you're postulating the chamber of a firearm is a totally sealed environment, you will experience a large gas loss. Most propellants are approximately 20% oxidizer, but taken as with any equation, the presence of atmosphere is a distinct part of it. It may even be opaque to most, e.g. not mentioned, but it's there nonetheless. In short, a huge decrease in gas-pressure by which to propel your round.

[Different skew if this is not an automatic, of course]

Seems to work OK (in near vacuum).
Ignoring the irrelevant gunpowder analysis, nitrocellulose with 8 oxygen atoms burns well in an inert atmosphere or a vacuum.

Seemed to work OK for the Russians (in hard vacuum).
http://www.russianspaceweb.com/almaz_ops2.html.
Admittedly, I have no idea what modifications were made to the 23mm Nudelman-Rikhter automatic cannon or it's ammo.

The major difference in internal ballistics is not having to compress and expel a column of air in the barrel ahead of the bullet. While this does mean the burning curve of the powder will be less than ideal, peak chamber pressure happens early in the bullet's trip down the barrel while peak air column resistance happens towards the end, so only the last half of the bullet's acceleration curve will be significantly changed.
While you could optimize the burn curve for space (and get better than atmospheric performance) it's still a fast and effective projectile with which the space hero can dispatch baddies.

Quercus
08-16-2011, 12:36 PM
I hope I'm not piling on here, but I wonder about a few of these.
The impact of the gun hitting the shooter's helmet might even leave a serious crack, so that the shooter dies both from decompression and oxygen-starvation.Anyone with any training in firing a gun will brace it against themselves, so there is no sharp impact; and in particular, guns are not usually held so that the stock impacts the shooter's face.

If you are on The Moon, with only one-sixth Earth gravity, firing two shots in quick succession will result in the second shot going wild.I'm not so sure about this. The muzzle of a gun fired on Earth rises because the gun is generally held on the lower side, and the recoil makes the whole gun rotate around the support point. On the Moon, a shooter doesn't need to support as much weight, so they'll be able to hold the gun with more even pressure on the top and bottom sides, so muzzle rise will be less (assuming, though, that the weight of the shooter is still enough to keep the shooter from moving significantly with the recoil).

In zero or microgravity (not the same) or even on a low-gravity environment like The Moon, the recoil from a gun aimed by sight will make the shooter tumble backwards head-over heels. It will also apply some thrust to the shooter, so that he/she will be thrust backward in space. There is no easy recovery when this happens, and when multiple shots are fired from the eye of the shooter, the tumbling can cause all the blood to run to his/her feet, making the shooter pass out and even die of oxygen-starvation to the brain.Now, the point about torque from the recoil causing tumbling is a good one. But I'm a little dubious about the tumbling being able to black out the astronaut. I can stand on my head, or hang upside down for reasonable amounts of time without passing out, so one gee of acceleration is bearable.

If I haven't screwed up the math, for a (tall) 2 meter person spinning around their midpoint, it takes a spin of 8 revolutions per second to create a one gee acceleration at the tip of their head.

And, using an astronaut of 75 kg (light, considering the suit needs to be included), and assuming a uniform mass distribution, I think (probably with a math error here) that an 8 Hertz tumble needs 6,400 Joules of kinetic energy, which is it appears less than a .50 caliber round, but needs three or four M-16 rounds. Since, unless you're braced against something, more energy is going to go towards linear backwards movement than tumbling, I think it would be hard to make yourself pass out by firing bullets in zero-G and causing yourself to spin.

Just trying to help in case any of your upcoming stories have this as a plot element. You know how science fiction fans are about accuracy.

Irishman
08-17-2011, 03:17 PM
Anyone with any training in firing a gun will brace it against themselves, so there is no sharp impact; and in particular, guns are not usually held so that the stock impacts the shooter's face.

At least with the right experience. I recall shooting skeet once where I gave myself a black eye from gun impacting my face due to trying to look down the barrel for aiming. Unfamiliar gun, not much experience.

I'm not so sure about this. The muzzle of a gun fired on Earth rises because the gun is generally held on the lower side, and the recoil makes the whole gun rotate around the support point.

Technically, the issue is that the line of action of the momentum from the bullet is above the line of action of the bracing - whether that is a pistol holding the grip below the chamber, or a rifle or shotgun with the stock against the shoulder. You are correct that part of the problem is the shooter is fighting gravity to support the gun until firing, but the real cause of the recoil shifting the barrel direction is the misalignment between the recoil and the support. If a handgun were built with the supports equally bracing the top and bottom and braced directly behind the barrel, that would not occur. (Well, autos/semi-autos with cartridge discharge would have a twist from the shell ejection, but the barrel wouldn't "walk up".)

But I think you are correct that on the Moon, the shooter could expend more strength balancing the bracing rather than supporting the weight, and control the recoil more tightly. But he might have to widen his stance a bit or something because his own traction is a bit less.

In weightlessness, the shooter is going to want some sort of stabilization and recoil prevention, or else the first shot will send him spinning. Not enough to black out or probably not injure himself, but enough to make semi-auto or autofire useless if not hazardous.

penumbrage
08-18-2011, 07:15 AM
You should be fine on the moon with just a wider stance (insert Sen. Craig joke here). You have the same mass to absorb the recoil, the only change is that the force required to push your center of gravity past the edges of your boots has been reduced to 1/6th.
If you need to have your hero shoot (or vector his thrust) accurately and repeatedly in zero gee, just have him brace his laser sighted firearm just above his waist, perpendicular to and at his center of gravity (your hero having practiced this technique to perfection in case his life depended on it).
Since Irishman is right, muzzle rise is designed into Earth guns (the recoil thrust line is always placed above the center of the grips or shoulder pad), the hero should cancel out this resulting angular momentum by rotating the weapon 180 degrees every other shot for relatively stable thrust.
His velocity and radial spin (imparted from revving the bullet to 50,000RPM) can be canceled with matching shots at the same CG but from the small of the back, either immediately (to stay stable for the rest of the gunfight) or after flying back to safety from certain death.
Just remember when using your MMU (munitions maneuvering unit) that your ride home may not be bulletproof.