Why would a man portable electromagnetic "rifle" need that much velocity?  Something along the lines of 4000fps for a >100grn bullet would be just fine.  Why the need for a large projectile?  More surface area for the magnetic field to grab?   Liquid/cryrogenic cooling.  Since the thing will need an electrical source to work anyways adding a compressor/pump & barrel jacket shouldn't cause that much more hassle.

Projectiles in a rail guns are accelerated by passing a current though a magnetic field.  The magnetic field in most rail guns is produced by the current flowing in the rails although an external field could also be used.  The armature (projectile) conducts the current from one rail to the other.  The length of this flow of current times the strength of the magnetic field produces a force on the armature and accelerates it down the rail.  So the longer the rails the more time force is applied to the projectile and the greater the separation of the rails the greater the force (for the same uniform magnetic field).  

The projectile NASA used is made of a very dense metal with a lightweight aluminum armature to hold it to the rails allowing for a lighter projectile of greater size.  When high amounts of current is passes through the armature it turns to plasma (a conductive gasses state) this would heat the gun quickly.  

The high velocity a rail gun can achieve is the major plus they have over chemical propellants.  You also want to surpass the escape velocity of the gravitational field you are in, as mentioned before.

Cooling the rails would most likely be necessary to make a small rail gun feasible.  Super conductor only work at very low temperature and with out them losses from resistance in the rails and power cords would be very high.

I wouldn't imagine a man-portable rail gun would have a rate of fire fast enough to have cooling problems.  Given that the system has a coolant system for the superconductive magnets, the recharging speed of the firing mechanism would be a big factor.  I would imagine a system like that would charge up much in the way a flash on a camera does.  A charging unit and a big capacitor to hold the charge.

rubberband gun.. the answer to all your outer space shooting needs..

Quoted: I wouldn't imagine a man-portable rail gun would have a rate of fire fast enough to have cooling problems.  Given that the system has a coolant system for the superconductive magnets, the recharging speed of the firing mechanism would be a big factor.  I would imagine a system like that would charge up much in the way a flash on a camera does.  A charging unit and a big capacitor to hold the charge.

Homopolar Generator would be a more likely power supply and would allow for burst fire.  I really like the idea of electromagnetic propulsion but I just do not see it as being feasible yet.  A nuclear power plant would most likely be needed for space because solar power would require huge arrays and other types of power plants would not work well in space.

A gyrojet style firearm would be the best bet because it has almost no recoil and would work well at extended ranges.  How far along has McUzi got on his gyrojet gun?  Dose he still lurk around here?  I would be very interested in hearing a progress report about his project.  All this talk has made me interested in trying to make something like that.

The University of Texas and the Army have put togeather a couple coilguns. One 25mm and one 90mm. The 90mm already beats the M256 120mm in performance and is itself small enough to fit in a AFV- unfortunatly its power supply still requires a 44ft shipping container.

the 25mm was built for testing as a machine cannon, it has demonstrated fireing at 600 rpm, on a par with the 25mm Bushmaster Chain Gun.

The coilgun is preferred now because it receves no wear, like the rails in a true railgun does. It has very little heat buildup, and does not require cryogenic cooling, the electromagnetic coils wrapped around the barrel just use plain copper. They use pulsed, not continuous, electrical power to get the megawattage up yet shrink the powerpack. The powerpack of choice is a stack of flywheels or "kinetic energy batteries" which UT Austin is also developing.

Someone correct me if I'm wrong but the space craft would be moving @ 17-18KM/H. Unless the shooter is bolted down he/she would be moving in relation to the space craft and the target both. If you are firing at a target that is with another space craft nearby that craft would be moving relative to the original craft the shooter and to the target unless the target is bolted down to the second craft. The calculations required would need a fairly large computer to calculate and an even bigger computer to calculate it quickly enough to avoid lag time. Plus you would have to have a fairly good sensor array to plot where everything is in relation to everything else and how fast and in what direction the target is moving in in relation to every thing else. and feed this data to the computer fast enough to prevent still more lag time. Plus the projectile would need some kind of thruster that would automatically do a reentry burn so that all "spent" rnds. would fall out of orbit and burn up. This would require an onboard computer and sensors for the projectile in order to calculate the burn. Even if we simplify the problem and allow that both shooter and target are bolted into the inside of the same space craft which is not spinning in any way (this would be necessary to prevent an artificial gravity effect)we would still need to fire not at the target itself but at the point in space where it will be after the transit time for the projectile. What is the lead for a target moving at 17-18KM/H?

Quoted: Someone correct me if I'm wrong but the space craft would be moving @ 17-18KM/H. Unless the shooter is bolted down he/she would be moving in relation to the space craft and the target both. If you are firing at a target that is with another space craft nearby that craft would be moving relative to the original craft the shooter and to the target unless the target is bolted down to the second craft. The calculations required would need a fairly large computer to calculate and an even bigger computer to calculate it quickly enough to avoid lag time. Plus you would have to have a fairly good sensor array to plot where everything is in relation to everything else and how fast and in what direction the target is moving in in relation to every thing else. and feed this data to the computer fast enough to prevent still more lag time. Plus the projectile would need some kind of thruster that would automatically do a reentry burn so that all "spent" rnds. would fall out of orbit and burn up. This would require an onboard computer and sensors for the projectile in order to calculate the burn. Even if we simplify the problem and allow that both shooter and target are bolted into the inside of the same space craft which is not spinning in any way (this would be necessary to prevent an artificial gravity effect)we would still need to fire not at the target itself but at the point in space where it will be after the transit time for the projectile. What is the lead for a target moving at 17-18KM/H?

That speed is with reference to the earth, if the two combatants where in similar orbits their relative velocities would be much less.  A missile would be good weapon for what you are talking about.  NORAD as talked about early can track orbiting objects very accurately.  Normal range in space combat would easily exceed 10,000 of miles, as there is no cover to limit range.  

If you wanted to destroy something in orbit a missile lunch from the surface would be the simplest option.  If you needed to capture a space station or craft then things would get more difficult requiring CQB in space.  What if combat took place inside a spacecraft?  What weapons would be needed to not damage craft and still incapacitate the enemy?

hOW ABOUT A BOW AND ARROW, OR A CROSSBOW? NO RECOIL, AND THE FORCE THAT PROPELS THE PROJECTILE IS NOT ACTED UPON BY THE SHOOTER. IT COULD WORK.

Bows have recoil just less than a gun. The string on a bow would have to be very special material to remain accurate and consistent in the temp. and pressure extrems of space. I think if CQB actualy took place inside a space craft then in would probably be in a vacume so I don't think air leak would be a problem. Damaging critical parts in the craft might be however. HighlandMac may be close to right any way. Some large relativly slow moving projectile might work well.

I made a fundimental mistake when I thought the bullet if fired would have no velocity relative to earth and would require a very long lead. The gun would be at orbital velocity so the bullet would be at orbital velocity after being fired and both the shooter and target would be at orbital velocity also. Zero velocity relative to each other and the bullet.

All I know if the guys in Star Trek next gen. or voyager had a belt fed Minmi or M60, they would mown down the borgs like grass.  Since the borg can adapt to differ phaser variance, they still can't stop a solid projectile.  therefore, no matter how advance the space guns get, someday they still need to come back to you good old firearms.

The Borg were supposed to have shielding but they still interacted with the environment around them, they touched things. The only way you could do that would be to have some "filter" on the shield that allowed slower moving objects to enter the field or a way to have the field turn of when approached by a slower moving abject.
God help me I'm turning into a Trekkie, where's my medication.

At any rate this suggest a Scottish Claymore would be an ideal weapon for Borgs.

Quoted: The Borg were supposed to have shielding but they still interacted with the environment around them, they touched things. The only way you could do that would be to have some "filter" on the shield that allowed slower moving objects to enter the field or a way to have the field turn of when approached by a slower moving abject. God help me I'm turning into a Trekkie, where's my medication. At any rate this suggest a Scoyyish Claymore would be an ideal weapon for Borgs.

I dont mean to cross sci-fi franchises, but remember the line from Dune, "The slow point penetrates". However the borg were, to varying degrees, cyborgs. That ment they had a lot of metal in them which would still defeat bullets

Quoted: Quoted: Re rail guns/Gauss guns & recoil: I'm not sure they'd have *that* much recoil, definately less than a conventional gun.  Deepends mostly on the slug fired.  Back when I used to play RPG's the SciFi game Traveller had rules for low & zero G combat.  The Gauss rifle used in the game was one of the most effective non energy weapons available.  Their version fired a steel alloy core needle like bullet with a soft alloy hollowpoint jacket.  No muzzle flash & virtually no noise other than rounds whistling by.  Another option in the game was a large caliber low velocity revolver firing explosive slugs.  Something like a .60 S&W Short at 400fps muzzle velocity.   Recoil can be described by the conservation of momentum.   Momentum:  p=m*v If a system of a gun and a projectile has 0 momentum before it is fired it will have 0 after it is fired as well. Mgun * Vgun + Mprojectile *Vprojectile = 0 So the gun will have a negative velocity (opposite direction from the projectile) when it is fired.  Most rail guns today are large but if one could be developed to be man portable in space it would have to be light and small enough to weld.  The velocities of the most powerful rail guns are over 50,000 ft/s.  It would not take a very massive projectile to cause a lot of recoil.  The projectile size also needs to be fairly large for a rail gun to work. Heat would be another problem in space.  With little air gun barrels would not quickly cool lowering the maximum rat of fire.

Well in one respect, EM guns do offer lower recoil than a firearm of the same perfomance. You have to add the energy generated by the mass and velocity of the POWDER to the weight and velocity of the projectile.

But we are still way off because, since no one has tested firearms in space to my knowledge, we dont know how much a firearm will gain from not having to push air in front of it down the barrel. Also, I am not sure that rifleing would offer a advantage in space, all weapons could be smooth bore so long as their projectiles had a interference fit all around.

Rifling would still help with dynamic balance.
Crosswinds would not be much of a problem however.

I mistyped Scottish Claymore, sorry.

The M41A pulse Rifle with over and under pump action grenade launcher, Shooting the 10mm explosive tip caseless, the standard light armor piercing round.
"aliens"

I think shooting in a space station would be more dangerous as discharging a firearm in a jetliner.  Not only is it a pressurized environment, but you've got to worry about damaging environmental support and power systems.  Everything aboard is essential to operation.  Even with some form of taser you'd still have to worry about piercing cables and shorting out equipment.

Ah, Star Trek:  Home of the convenient inconsistency!

STII: The Wrath of Khan:   Note to Captain:  When battling another ship in the Mutara nebula and the viewscreen doesn't work and neither do your instruments that can locate the other ship, send crewmen to various windows and have them plug portable cameras into the video intercom system and point the cameras out the windows.  Use VISUAL AIDS.

Voyager:   How convenient that you encounter more than one superfast transportation technology, they work for you in a pinch, and then they can't be used again due to some ill-defined 'incompatibility' with the ship's systems.   Is Microsoft writing the ship's operating system or what?
Slipstream, transwarp drive, whatever.  All worked once, and this crew can pull a six-legged rabbit out of its ass on a moment's notice.  Yet they can't make these devices work again???

Implausible, I say!

CJ