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Physics/Firearms for variable gravity and/or microgravity


Dear Mr. Nelson,

Hello, and thank you for being willing to answer questions. First, I would like to let you know that I very much respect your time, and that I really am working on writing science fiction, and that I have tried to think carefully about my questions for several years so as to avoid asking stupid things. I have been to college, and I did well, but did not take much physics.
I have some questions and some points to ask for your opinion on, if you have time:

In various places, it has been repeatedly claimed that since gunpowder includes its own oxidizer, a gunpowder-using firearm MIGHT be able to function in microgravity -- at least for a while. On the other hand, it has been said that a typical firearm built for use in oxygen atmosphere at 1G may soon seize up due to lubricants freezing or melting (temperature gradients due to varying locations of heat sources in space, varying effects of solar radiation falling on some objects but not others, motion of the objects on which the light is falling, convection through the weapon ...)

Suppose that the technique of using springs in the firearm action has been replaced by inert silica hydraulic technology, so there are no springs and I don't have to worry about them failing. Suppose that my lubricant is made from living cells in suspension, similar to a genetically engineered alga. So, my lubricant is alive, metabolizes dust, and can go dormant for long periods before returning to normal.

In order to avoid punching through walls that I do not want to punch through, we may suppose that I have frangible ammunition, or that my firearm uses binary liquid propellant that allows me to adjust the muzzle velocity. Perhaps I have an integral targeting computer that can read the density of the object to be fired upon, thus attending to such adjustments automatically. Certainly we can suppose that the digital sight will correct the point of aim for any atmospheric resistance or any change in the value of G that may occur when I deploy to a new place. And after all, I might need to go to a place where stronger gravity is simulated by the use of centripetal force, Might this cause me to think that my lower body was heavier than my upper body, requiring the computer to  correct for that as well?

I have only two more questions. Given that I need a system that is resilient against changes in temperature, do you think the soldier's firearm should have a form-fitting external layer with a gap having no air in between, almost as though it were a submarine with an inner hull and outer hull? After all, vacuum flasks for holding beverages employ such a technique. An of course, some immensely powerful anti-materiél sniper rifles use an analogous method such that the rifle has its real working parts free-floating inside a conformal, close fitting enclosure with springs in between. But so far, in real life, this has all been to manage the felt recoil on the big rifles. I thought perhaps that would be better than adding a complicated system with some sort of recirculated liquid to manage the firearm's temperature.

Here is the second and last question. Ben Bova's novel called "Privateer" has a sequence in which Russian space-mobile forces receive orders to conduct a visit, board, search, and seizure operation on a crewed space station which belongs to Venezuela. Boarders find a crewman on the outside of the hull that they are assaulting. They see him as an enemy combatant, and open fire.

We are told how the Russian soldier sees the trail of burning gunpowder hanging in space, in a line behind the path the projectile has followed. We are told how the attitudinal jets on his suit have corrected for him being pushed by firearm recoil. We are told that the Brownian motion caused little clumps to form, so most of the gunpowder behind the bullet burned smoothly, but some tiny specks are still hanging in space, visibly burning after the bullet has passed.

I have read many such books. Some books mention how, if you go to an offworld place, atmospheric resistance against projectiles may change. Fires may not burn, may burn with different size or different shape or different color that what you expect. Perhaps, if your firearm uses cased ammunition, and you go to an offworld place, empty casings may move in a different manner that what an untrained person will expect. But before I read that book, I had never known the concept of streams of gunpowder hanging behind projectiles when firearms go off in microgravity.  I wonder wether you think that it would happen.

Thanks very much.

You can have a monopropellant, like gunpowder. No big deal and no need for the complexity of a binary propellant.  There's no need for the layer you mention, and basically the trail can be explained by general motion through the gun barrel, just like the motion of the bullet.  


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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