Why doesn't the SGC have laser weapons?

[Exiled Master]

I'm personally of the opinion that we may see gauss guns (aka coilguns), at least on a larger scale, first. While they do have their own set of problems, they also have advantages, such as the fact that since the projectile is magnetically levitated, it has no moving parts to wear out. It also doesn't have frictional losses with the rail and few issues with the material flexing and wearing and needing to be replaced frequently.

gauss/coilguns
railguns

I'm still trying to figure out the difference between gauss guns and railguns. I really want to see a field deployed variation of one of them, though. But it would be an awfully big error to say that you could deploy such weapons with significantly more power using infantry.

[RA the sun god]

just like to say that the weapon on the pro was a asgard pulse weapon and after the goauld were defeated the asgard took it back..just to clear things up...

[immhotep]

just like to say that the weapon on the pro was a asgard pulse weapon and after the goauld were defeated the asgard took it back..just to clear things up...

and you would know this how?
did you read whilst copying stuff of Sgtech.net, or was this some miraculous teaser that escapes Gw's radar?

[RA the sun god]

ur right its off of sg-tech well done u...

[immhotep]

thanks.....can i stay there? FYI its an asgard energy array, not pulse cannon.

[RA the sun god]

well all the places i go say pulse cannon...ok

[immhotep]

just not the place you copy from apparently.

[RA the sun god]

oh dear the baby is still having a go...give it a rest...

[David]

I'd like to see both of you take a bit of a time-out from this thread. Just a brief one. This 'neener-neener' tug is not as amusing from the outside.

[RA the sun god]

I'd like to see both of you take a bit of a time-out from this thread. Just a brief one. This 'neener-neener' tug is not as amusing from the outside.

fine

[Avatar28]

I'm still trying to figure out the difference between gauss guns and railguns. I really want to see a field deployed variation of one of them, though. But it would be an awfully big error to say that you could deploy such weapons with significantly more power using infantry.

The links I posted would give more detail, but in short:

Rail guns use something called the Lorentz force to propel a projectile up two parallel rails. It's the same principle that electric motors are based on I believe. The biggest obstacle here is the fact that it requires very large currents (on the order of a million amps) and that the current and heat from the friction between the projectile and the rails has a nasty habit of vaporizing the rails. It also puts a lot of force on the rails which tend to bend and twist away from the projectile and results in arcing, etc and further erosion. Currently we're only able to get about one shot from a railgun before it has to be serviced.

Coil/gauss guns use an alternating series of magnetic fields. A powerful electromagnetic is switched on, pulling the projectile towards the center of the coil. As the projectile reaches it the coil is switched off and the next coil is activated pulling the projectile further along. In current designs there is typically a track that the projectile rides along. The biggest problem with coil guns is the fact that electromagnets take time to reach full strength after current is applied and for the strength to drop afterwards. One way around that is to use superconducting magnets but that has it's own set of problems. With a large gun such as could be mounted on a ship, these problems are less (it's possible to keep the magnets cooled enough and the longer distance makes it easier anyway).

I recommend you read the wiki articles I linked to for more info and better descriptions and diagrams of the whole thing.

[AcidSquid]

Why can't they use adapt the technology and make them earth style? I mean it might be just a special effects issue with money due to the fact that this is a TV show or was there an episode that I missed where they explained why they could not have an earth laser weapon even on promethus or the deatlus.

Because I said so.

[helio9]

While Gauss guns have clear advantages, rail guns are more efficient power wise, and while I'm not sure on this, everything I've read leads me to believe that rail guns have more potential in military applications.

[CHEL NAK GUY]

Hey guys.
I think that The SGC should modify the kull warrior's laser arm band and have them as a defence that are attached to the side walls and can be controlled from inside the control room, i think they would be useful because of the burst rate and effectiveness or they could do dome thing simular with zat guns. just a thought

[Avatar28]

While Gauss guns have clear advantages, rail guns are more efficient power wise, and while I'm not sure on this, everything I've read leads me to believe that rail guns have more potential in military applications.

I decided to do a little research on that and found this:
http://www.oz.net/~coilgun/theory/electroguns.htm

I'm going to quote a couple of little snippets for comparison

Railguns can operate in two distinct modes. In the metallic conduction mode, current flows through the sliding projectile itself, and this mode has been demonstrated to a performance level of about 1 kg mass and 2,000 g (20,000 m/s2) acceleration by the switching gun used in the Canberra installation to feed the main gun. Marshall and Barber tound that if the railgun is driven very hard, a plasma arc tends to bypass the projectile, leaving it behind. By using a non-conducting lexan projectile and confining the arc behind it they were able to achieve a performance level of 16 gram accelerated at 250,000 g along a 5 m barrel to a final velocity of 5.9 km/s.

To a great extent, the practical limit of rail guns will depend on acceptable cost and service life. The problems relate to mechanical containment of the percussive expansion force which tends to blow the rails apart, the electromagnetic analog of barrel pressure in a chemical gun, with the important difference that the railgun maintains more or less constant pressure throughout the acceleration. Instead of chemical corrosion, there is the destructive effect of high brush current density and the related metal vapor arc.

n addition to these limits, the classic railgun also faces certain fundamental lmimits which are not related to acceleration, but to maximum possible length or maximum muzzle velocity. As a railgun is lengthened, the resistance and inductance of the rails eventually absorb a dominant fraction of the energy. The effect is seen to begin at about five meters in the Canberra tests. Increasing velocity also causes an increasing back-emf. Current will continue to flow, even if this emf exceeds the output voltage of the homopolar generator, because the intermediate storage inductor acts as a current source. However, there is a practical limit to the voltage which can be stood off by the gap between rails, and this scales about linearly with size. Thus there are two fundamental effects which limit the amount of energy that can be transferred to the projectile, regardless of how much is available.

Another shortcoming of the railgun is its inherent inefficiency. An appreciable amount of energy is contained in the rail inductance at the instant the projectile leaves, and this energy must be absorbed by a muzzle blast suppressor. A fraction migh conceivable be returned to the homopolar generator. There are several means for circumventing the limitations of the classic railugn.

So railguns have high acceleration, 2 thousand to 250 thousand g, depending on the mode. Of course this also has a downside in that this sharp acceleration produces a lot sharper recoil.

Now for the coil/gauss guns (also referred to here as mass drivers). Note that part of the concepts described here involve the use of a "bucket" that carries the projectile within the gun but is not, itself, fired.

Mass drivers can operate in the "push-only" mode as in the case of Mass Driver One, or in the pull-push mode of Mass Driver Two, now under construction, in which each drive coil undergoes a complete sinusoidal oscillation by being connected synchronously to a supply capacitor line. By tuning this cycle to the effective wavelength of the bucket it is possibe to achieve energy transfer efficiencies, electric-to-mechanical, of better than 90 percent. We should add that the bucket-to-payload ratio is about unity, and that about half the bucket energy is recoverable by regenerative braking.

For all practical purposes, mass drivers have no velocity limit and no length limit. Acceleration has been limited thus far by the current and voltage capacity of the SCRs used for switching. Using shelf components, Mass Driver Two should achieve 500 to 1,000 g. If the SCR limitation is removed, by using ignitrons, spark gaps, or direct contact switching, performance will be limited by mechanical and thermal failure of the drive coils. Some preliminary calculations based on a four inch caliber mass driver using aluminum bucket coils and copper drive coils suggest an acceleration limit between 100,000 and 250,000 g. This is comparable to railgun performance. however, the failure mode of drive coils under fast pulse conditions is a very complex subject requiring experimental study.

So currently railguns have much higher accelerations than current coilguns however much of that limitation is in the hardware used to handle switching the coils on and off. If that limitation is removed, accelerations are much higher, comparable to the high end of a railgun. The coilgun also has the advantage that there is no real size limit to it so it could easiliy be 30, 40, even 100 meters or more long. Railguns are somewhat simpler and have (currently) much higher potential acceleration rates but have materials issues with the rails eroding and warping such that the rails need replacing after every shot. Building a power supply able to supply sufficient currents is also an issue. It is, theoretically possible to string multiple railguns together but that introduces a whole other set of problems so we'll disregard it here as impractical for the forseeable future.

Incidentally, we can calculate, based on the above, the maximum speed of the railguns we saw in Atlantis, assuming the figures hold true (which they should be fairly close since it's as much a limit of physics as anything). Based on pictures I could find, by comparing it with the soldiers, I would estimate the length of the railgun as around 3 meters. We'll be generous and use the 250,000 G acceleration. Doing the math I come up with a speed of around 3834 m/s or about mach 11. With a limit of 5 meters you could eke out about 5000 m/s or mach 14.5. Even if the Prometheus/Daedalus's main railguns could fire a larger projectile at that speed, say 2kg, you still end up with a kinetic energy on the order of 25,000,000 joules.

For comparison, the 16" guns on the Iowa class battleships fired a 2000 lb shell with a muzzle velocity around 2500 m/s giving an energy of 2,800,000,000 joules, over 100 times greater.

Just for fun, let's consider if the Daedalus class ships were equipped with a coilgun most of the length of the ship. I believe it's been estimated at around 350 meters or so in length so let's say the main gun is a coilgun of 300 meters length down the main axis of the ship. The link above didn't seem to give a limit for projectile size for the coilguns so we'll run a couple of different ones. 300 meters with an acceleration of 250,000 G gives a muzzle velocity a bit over 38,000 m/s (mach 112), also just under escape velocity for the sun at the location of the earth.

Anyways, a 2 kg projectile at that speed yields 1,444,000,000 joules, about half that of an Iowa class battleship. A 50 kilo projectile gives you 36,100,000,000 joules.

1 joule = amount of energy produced by 1 watt for 1 second.

Basically for a main weapon a railgun (unless they've managed to string them together) sucks. A coilgun would be much better in that regards if you've got the length to have a long run. For a smaller sized weapon (such as the point defense railguns we've seen in Stargate) it could be pretty much a tossup I'd say.