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The Annoyed Man wrote:

Purplehood wrote:As I understand it, heat-dissipation in space is a big issue and not nearly as easy as we imagine. Large surfaces are required to speed-up the process. I imagine that a Machine-gun barrel in space would have a difficult time "cooling off".

Well yes, it would; but my hypothesis has to do with heat dissipation through radiant light. Light does not require a medium to transfer. Heat is energy, and the barrel heat is merely the product of the kinetic energy transfered into the barrel from both the friction of the bullet's passage, and the transfer of heat into the barrel from the combustion gases as they travel down the barrel behind the bullet. (There would also be some energy transfer due to the elastic expansion and return of the chamber under each detonation, but that would be a relatively small percentage of the total.) IF enough energy from friction and hot gas gets transfered into the barrel at a faster rate than it can dissipate that energy, it will glow red (then orange, then yellow, then white, if it gets hot enough). We know this to be true from simple observation. That glowing means that the pent up energy which has been transferred into the gun barrel has risen into the visible spectrum because it has been acquired faster than it can be dissipated.

My hypothesis is that, A) since we know from observing the stars that visible radiant energy does not require a substrate (atmosphere, water, etc.) to dissipate; and B) we know that a white hot barrel is hotter than a red hot barrel and a red hot barrel is hotter than one which no longer radiates light energy; and C) since we know that stars change color as they cool; then we can extrapolate that, once firing ceases, a red hot gun barrel will in fact cool in space at a relatively rapid rate until it has dissipated enough heat energy that it can no longer emit that energy as light. Up to that point, it will cool at a much more rapid rate than a star does simply because of the mass and energy differential between a star and a gun barrel. Beyond that point, the rate of heat loss will slow down dramatically because A) heat energy in the non-visible spectrum requires a substrate to transfer itself out of the object containing it; and B) the only matter in contact with the gun is that part of the astronaut's (insulated) space suit which is holding the gun. The same principle would apply if it is hard-mounted to the exterior of a spacecraft, in which case the heat energy is managed by the spacecraft's cooling system. If the hard-mounted gun is insulated from the spacecraft's cooling system, then it will cool at a very reduced rate once the heat's energy has decreased to below the visible spectrum.

Are there any flaws to my reasoning?

Now I've got to get back to work.

george wrote:Gravity is still involved, you know.