Souyuz VI (Almaz) carried a recoilless gun 23mm gun for self defense
http://astronautix.com/craft/almaz.htm

Would be the muzzle velocity of a 23mm round fired in a vacuum with no gravity be the same as on Earth, and its range practically infinite?

Yes, practically. The muzzle velocity is at the termination of the acceleration phase, so the little air that would provide resistance in the barrel on earth would be all the difference. However, the "recoilless rifle" is another term usually used for rocket-propelled projectiles. (The bazooka was technically a 90-mm recoilless rifle...)

Gun barrels get very hot, wouldn't overheating be a problem in the vaccum?

Yes, it should be the same. As for recoilless, how would that work? Any gun that is not rocket powered is not recoilless. Think of it this way - say you had a projectile that was accelerated to 800m/s. That would take a force (probably a pretty large one, for a 23mm cannon round to accelerate in a few meters). According to Newton's 3rd law, the equal and opposite force would be applied to the cannon, creating a recoil. Eventually, this force could have a pretty large effect on the velocity of the spacecraft.

Probably not. Gun barrels would heat significantly only with repeated firings. I dare say a gun intended only for self-defence wouldn't be fired that often.

In any case, it probably wouldn't be hard to redesign it in some way which allowed it to radiate heat more efficiently than the basic design would.

You'd have to have an active cooling mechanism on the barrel in order to cool it effectively. Thermal radiation is the least effective method of transfering heat.

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Fair enough. The point I was making was that they wouldn't have sent up the weapon without modifying it for the local conditions.

I have a question, though: self-defense against who? Were they imagining ETs, or that NASA would attack them in orbit??

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The Encyclopedia Astronautica entry you linked to states that the gun was for use against 'Apollo type' atackers so I could think that the planned enemy was NASA or the USAF.

You have to remember that the linkage between the Russian space program and their military was much tighter than that between NASA and the US armed forces.

While not stated in the entry, an equally likely target would be any US/Western communications/Photorecon satelite in range.

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Could they nail one of our satellites and pass it off as a micrometeoroid strike?

A space station isn't a good attack plattform. It would be like using oil rigs for attacking ships.

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Anyone catch this interesting tidbit as well?

The gun may actually have been fired in space
http://www.fourmilab.ch/documents/spaceguns/

The US had some 'satellite inspector" missions involving Gemini--which was close to the original Almaz.

Almaz--set the standard for the DOS core block that was Salyut, Mir, and the ISS Zvezda module. It was to have a capsule in the nose--and a hatch through the heat shield back to the compartment. The TKS Ferry/FGB tug (later the Spektre mdules plugged into Mir) was also to have such capsules but those were replaced with Soyuz docking hatches.

Such Almaz and TKS/FGB were to be launched by Proton, while our Gemini/MOLs were to be launched by Titan III--one boilerplate was in fact launched.

There were some armed Gemini concepts floating around.

Check out www.up-ship.com for more.

It may be used that way, but it is incorrect. True recoilless rifle fires orinary shells and all acceleration occures inside the barrel, but it has an opening in the rear through which hot gases escape. Instead of the gun being shoved backwards, you have a backward stream of hot gas with kinetic energy equal to that of projectile. Gun structure remains immobile:

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

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In addition, objects in orbit are moving at orbital velocity. PDQ. Also, ranges in orbit would be hideous. You'd have a weapon with unlimited range, but what good does that do you when the things you want to shoot at (in this case, satellites) are small, fast, and really far away?

Remember that we've tested guided missile interceptions with only limited success.

Faultline

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