Starfleet Jedi

There have been attempts to gauge the relative firepower of certain guns by comparing their barrel lengths, operating under the assumption that a gun that is ten times as long will have 1000 times the volume and thus also have 1000 times the firepower. Of course, some have responded by questioning the relationship between a gun's volume and its firepower. This subject came up during my stint on SDN, and shortly before I left, I went through the trouble of doing a case study (which, IIRC, I never actually posted. Oops.) based on the Iowa class battleship.

The Iowa had 9 16-inch Mark 7 guns, 20 5-inch Mark 12 guns, 80 40mm Bofors guns, and 49 20mm Oerlikon guns. Some research turned up the following information:

The Mark 7 gun had a length of 20.3 m and could fire a 1225 kg armor-piercing projectile at 762 m/s, or it could fire a 862 kg high-explosive shell at some 820 m/s.

The Mark 12 gun had a length of 5.83 m and could fire a 25 kg shell at 760 m/s.

The Bofors 40 mm had a length of 2.25 m and could fire an 0.9 kg projectile at 900 m/s.

The Oerlikon 20 mm had a length of 1.4 m and could fire an 0.13 kg projectile at 820 m/s.

It's fairly easy to use Microsoft Excel to graph the relation between the length of each gun's barrel to the kinetic energy of its projectiles, and from there it's even easier to get a regression line that fits the data fairly well.

If L is barrel length in meters and E is kinetic energy of the projectile in Joules, then for the set of guns aboard an Iowa class battleship, the following equation approximately holds:

E = 20002 * L^3.2402

For whatever it's worth, R^2 = 0.9963, which means that the above equation fits the data pretty damn well.

So what does this mean?

Well, it means that, for projectile weapons at any rate, the relationship between volume and firepower is actually pretty close!

Mike Wong says that the "light turbolasers" aboard an ISD can produce about 1500 TJ of energy. We'll take this as a theoretical upper limit. MW also says that the heavy turbolasers aboard an ISD are some 5x longer. If the above relation works for energy weapons as well as projectile weapons, the heavy turbolasers aboard an ISD would be some 184x as powerful as the light turbolasers. That gives us an upper limit of about 276,000 TJ for heavy turbolasers. For those who prefer their data in terms of TNT equivalence, light turbolasers peak out at around 375 kilotons, and heavy turbolasers peak out at 69 megatons.

These are probably generous upper-end figures, given the explosive nature of the Hoth asteroids, the fact that they were less than half the size MW said they were, etc. etc.

Anyways, just food for thought.

Add a rail gun to your chart and it'll break it.

Indeed, modern firearms bend it. The .17 HMR is a wee bullet fired hella-fast and rated at around 335 joules. The .22 LR is larger and slower in normal loads, topping out around 200. US Army .45 ACP is big and slow, rated at about 475 . . . about the same as the .22 Magnum . . . but modern tactical loads can break 825.

Of course, .45 is a pistol round, so let's pick something else . . . how about the 7.62x51 NATO as one might fire from an AK-47? It is close to the .308 Winchester, which hovers around 3600 joules.

That's three barrels ... .17, .22, and .308 ... and they're all over the place. And that's just projectiles with powder propellant.

What are the issues involved with blasters and turbolasers? What's involved in propelling those galvened particle beams with radioactive material inside that disperses into a fog when the galvening fades? Does that scale? Is the density the same? Are there considerations in the design for refire rate? Is there something else that would make it harder to scale up, so that a gun X times the size only gets .1X or .001X more powerful?

Barrel scaling only proves that the scaler has done the scaling. While an interesting argument from general concepts, it is proof of nothing when, as we have seen, it is not supported canonically.

Picking the length alone would be insufficient anyway. Consider the whole volume for starters. The length is more or less related to guidance and precision, therefore range, and also speed for it allows the explosive charge pushing the projectile to apply its expansive forces for a longer time frame, hence a somewhat faster muzzle speed.
Barrels in SW would fit as part of a coilgun design.
But the size of the barrels is not that reliable. The huge cannons on the Trade Federation Control Ship were used to shot at anything between a fighter and a small cargo ship, at either long range or close range. Although probably most suited for larger targets, they did hit some N-1 starfighters. On the other hand, the double barreled turbolasers in the Death Star's trench weren't exactly the longest ever, yet belonged to a network of defenses said to be most suited for dealing with quite larger targets than those snubfighters.

The Death Star trench turbolasers always kind of baffled me once I got over the coolness factor of the visuals. Why have such guns like that and especially guns that while they provide a tight screen that the Rebel starfighters could barely squeek by between, their inability to elevate or rotate the turrets to hit the small ships just never seemed to be there. So if the were fixed, or nearly immobile emplacements, what the hell were they doing in the trench like that?
-Mike

2046 wrote:Add a rail gun to your chart and it'll break it.

Yes. But I wouldn't include a railgun in this particular data set any sooner than I'd include a laser.

Indeed, modern firearms bend it. The .17 HMR is a wee bullet fired hella-fast and rated at around 335 joules. The .22 LR is larger and slower in normal loads, topping out around 200. US Army .45 ACP is big and slow, rated at about 475 . . . about the same as the .22 Magnum . . . but modern tactical loads can break 825.

Of course, .45 is a pistol round, so let's pick something else . . . how about the 7.62x51 NATO as one might fire from an AK-47? It is close to the .308 Winchester, which hovers around 3600 joules.

That's three barrels ... .17, .22, and .308 ... and they're all over the place. And that's just projectiles with powder propellant.

Well, if I'm right about barrel scaling, all those differences would end up more or less averaging out. But what I'd need would be a list of guns, not a list of ammo types.

And of course, it would be even better to get a list of more guns that were mounted on naval ships in the mid-to-late 20th century. I'll get on that and see how it goes, and post my results later.

If you provide a list of guns (not bullets, please) that you think would make your point and throw a wrench in the works of this whole barrel-scaling thing, I'd be glad to quantify how effectively they do so. But at the moment, the equation fits the data very well. (R^2 = 0.9963)

What are the issues involved with blasters and turbolasers? What's involved in propelling those galvened particle beams with radioactive material inside that disperses into a fog when the galvening fades? Does that scale? Is the density the same? Are there considerations in the design for refire rate? Is there something else that would make it harder to scale up, so that a gun X times the size only gets .1X or .001X more powerful?

I can imagine cases where a gun 10 times as long might be 100 times more powerful instead of 1000, eg cooling systems being the main limiting factor on how much dakka the gun can put out (scaling with surface area instead of volume), and I can imagine someone making the case that this is what's going on with turbolasers.

But in the absence of such a case being made, is it really unacceptable to attempt to glean information from the obvious real-world analogue? It's pretty obvious that a Star Destroyer is supposed to be a cross between a battleship and an aircraft carrier IN SPAAAACE, so what's wrong with treating it like one?

Barrel scaling only proves that the scaler has done the scaling. While an interesting argument from general concepts, it is proof of nothing when, as we have seen, it is not supported canonically.

I'm rather new to the debate. Might I ask what it is you have seen in the Star Wars canon that indicates that barrel scaling wouldn't work for Star Destroyers the way it seems to work for battleships?

It's not really something in the canon, and it's not that the relationship is not true. It's just not a good estimate for turbo-lasers because the relationship describes modern projectile weapons and relies on the physics of how an why bullets travel the way they do, and turbo-lasers are not bullets they are particle weapons. So I guess that's what's in the canon showing the relation to be inapplicable, turbo-lasers are not bullets.

The relationship exists due to factors such as rifling, gas pressure, and projectile mass. All of which are factors in determining flight paths for bullets. Turbo-lasers, however, lack rifling and gas pressure, thus making the equation inapplicable because it relies on factors that are inapplicable to this type of projectile. Much in the same way the relation would not apply to a flamethrower, a laser, or a rocket launcher.

Now if we knew the function of the barrel we could make some simple geometric relationships. For example, if they were used for heat dissipation, than the power would be related to their surface area. If turbo-lasers had a fixed energy density, than their energy would be proportional to the barrel's cross sectional area. If the bolt were totally formed in the barrel and then shot we could say the energy would be proportional to the volume. But we don't know enough information to say why they are built the way they are, or even why they have a barrel. All we know is that turbo-lasers are directed energy particle weapons.

Mike DiCenso wrote:The Death Star trench turbolasers always kind of baffled me once I got over the coolness factor of the visuals. Why have such guns like that and especially guns that while they provide a tight screen that the Rebel starfighters could barely squeek by between, their inability to elevate or rotate the turrets to hit the small ships just never seemed to be there. So if the were fixed, or nearly immobile emplacements, what the hell were they doing in the trench like that?

The barrels appear to be able to elevate much like the barrels on the towers at the edge of the trench that fire up at the x-wings as they make their approach.

Mike DiCenso wrote:The Death Star trench turbolasers always kind of baffled me once I got over the coolness factor of the visuals. Why have such guns like that and especially guns that while they provide a tight screen that the Rebel starfighters could barely squeek by between, their inability to elevate or rotate the turrets to hit the small ships just never seemed to be there. So if the were fixed, or nearly immobile emplacements, what the hell were they doing in the trench like that?
-Mike

I had the same question. Then I remembered the cannons placed on the side of age of sail warships, or within confined spaces on the rim of forts' defenses, right up to WWII with cannon pieces and their muzzles sticking out of slits from bunkers facing seas.
These are pieces that would only get fired once the enemy crosses the line of fire, a bit like those odd side cannons fired during the short exchange between a Clone Warship and the Invisible Hand.

But I recall they were TLs right on the edge of the cliffs bordering both sides of the trench, and probably a good many pieces placed here and there on the surface.
Technically, it isn't a bad thing to have some of these weapons tucked down a protection of some kind, although it does indeed reduce their ability to shoot at anything not coming up at the horizon of the trench's end or right above them.

359 wrote:Turbo-lasers, however, lack rifling and gas pressure, thus making the equation inapplicable because it relies on factors that are inapplicable to this type of projectile. Much in the same way the relation would not apply to a flamethrower, a laser, or a rocket launcher.

Gas pressure might very well intervene at some point if one considers bolts to be a complicated compound where plasma and, well, light are mixed together.
Whatever. :)
For the sake of it, unless you want to go with the pure light explanation and then face recoils that warrant the firing insane levels of biggawatt laz0rz, you might very well want to accept the idea that the projectiles are both solid, volatile and yet mostly made of temporarily "glued" together non-photonic particles, yet do contain a soft and tender heart of delicate photons.
Comes sometimes with cherry flavour.

Moff Tarquin wrote:

2046 wrote:Add a rail gun to your chart and it'll break it.

Yes. But I wouldn't include a railgun in this particular data set any sooner than I'd include a laser.

It's a projectile weapon with a barrel, too. While many SW blaster/turbolaser weapons have a barrel, some seemingly do not (e.g. TIE), so there is a similar discontinuity of tech which is what I was aiming for.

But what I'd need would be a list of guns, not a list of ammo types.

Your post featured barrels and related ammo types for 'yield' calcs related to the barrel. So did mine. The point stands.

is it really unacceptable to attempt to glean information from the obvious real-world analogue?

It's okay as a prima facie sort of thing as a ballpark conjecture, but when it breaks down it must be acknowledged. And its limitations for use must be acknowledged.

Focusing on WW2 weapons, for instance, puts the focus on a certain metallurgical tech base where chamber pressures and such all had certain similarities, adjusting for scale and other factors. And yet, a modern +P+ sort of round might blow up an old gun. However, if you imagine a modern civil war, or even a modern war period, weapons of various ages will be seen in use. The same is true of Star Wars.

And then one must cross-check the conjecture against the canon, too, and there it is wanting. The scaling that suggests 69 megaton turbolasers is just wrong, as there are no such shots observed. The highest known yield in the canon for turbolasers is around a megaton, IIRC, and no other shots come close to that novel reference.

2046 wrote:The highest known yield in the canon for turbolasers is around a megaton, IIRC, and no other shots come close to that novel reference.

Vaporized small town?
Open to conjecture. Besides, unless the novelizations get edited again under the new publishing organ, aren't they old hat now?

2046 wrote:

Moff Tarquin wrote:

2046 wrote:Add a rail gun to your chart and it'll break it.

Yes. But I wouldn't include a railgun in this particular data set any sooner than I'd include a laser.

It's a projectile weapon with a barrel, too. While many SW blaster/turbolaser weapons have a barrel, some seemingly do not (e.g. TIE), so there is a similar discontinuity of tech which is what I was aiming for.

So far as I am aware, the term "turbolaser" has denoted only artillery-like weapons, never anything on something as small as a fighter, let alone a hand-held weapon.

However, the discontinuity is noted.

But what I'd need would be a list of guns, not a list of ammo types.

Your post featured barrels and related ammo types for 'yield' calcs related to the barrel. So did mine.

To quote myself:

The Mark 7 gun had a length of 20.3 m and could fire a 1225 kg armor-piercing projectile at 762 m/s, or it could fire a 862 kg high-explosive shell at some 820 m/s.

The Mark 12 gun had a length of 5.83 m and could fire a 25 kg shell at 760 m/s.

The Bofors 40 mm had a length of 2.25 m and could fire an 0.9 kg projectile at 900 m/s.

The Oerlikon 20 mm had a length of 1.4 m and could fire an 0.13 kg projectile at 820 m/s.

In order to add something to the spreadsheet, which I would need to do in order to quantify how your counterpoint effects my point, I need four things: The name of a gun, the barrel length of said gun, the mass of its projectile, and the muzzle velocity. If any of those things is missing, I am unable to include it in the graph that gives me the equation and the R^2 value. Without the R^2 value, I can't tell how well the equation fits the data.

As things stand, your data is in an unusable form. Would you be willing to provide it in a more usable form, so we can see just how this particular point of yours effects my position?

The point stands.

And at the moment, it stands still. If you provide all four data points for each ammo type as I requested, your point will move. Maybe it will fall to the ground in defeat. Maybe it will drive implacably forward crushing my point into the dust. I don't know which, but my inner scientist is all aquiver with excitement to find out. Isn't yours?

is it really unacceptable to attempt to glean information from the obvious real-world analogue?

It's okay as a prima facie sort of thing as a ballpark conjecture, but when it breaks down it must be acknowledged. And its limitations for use must be acknowledged.

Agreed. If the limiting factor of a turbolaser's firepower is not related to volume, but to surface area (eg, for heat rejection reasons), turbolaser firepower would scale with the square of barrel length as opposed to the cube. Additionally, we don't know all that much about what a turbolaser actually is, so any sort of speculation of this type is - if you will pardon the pun - a shot in the dark. But the very fact that we don't have all that much to go on is reason enough to be engaged in this sort of wild speculation, in my opinion.

C'mon, Mr. Moderation. Try the wild side of the force. ;)

Focusing on WW2 weapons, for instance, puts the focus on a certain metallurgical tech base where chamber pressures and such all had certain similarities, adjusting for scale and other factors. And yet, a modern +P+ sort of round might blow up an old gun. However, if you imagine a modern civil war, or even a modern war period, weapons of various ages will be seen in use. The same is true of Star Wars.

Fair enough. In your estimation, what are the odds that turbolasers of different eras have been mounted on Imperial star destroyers?

And then one must cross-check the conjecture against the canon, too, and there it is wanting. The scaling that suggests 69 megaton turbolasers is just wrong, as there are no such shots observed. The highest known yield in the canon for turbolasers is around a megaton, IIRC, and no other shots come close to that novel reference.

To quote myself:

These are probably generous upper-end figures, given the explosive nature of the Hoth asteroids, the fact that they were less than half the size MW said they were, etc. etc.

The 69 megaton figure was intended as an absolute maximum, not the real value. I'd imagine that a generous 75 megaton figure offered by a certain reliable source was intended to serve a similar purpose.

If we assume a 20 m wide asteroid, we bring the value for light turbolasers down to 250 TJ. Account for the fact that the asteroids are not particularly hard to "set off," and we end up with maybe 100 TJ. Multiply that by 184, you end up with 18.4 PJ, or around 4.6 megatons.

Incidentally, if we use the aforementioned reliable source's method, ~5 megatons is around the energy it would take to vaporize a 1969 Ford Mustang Mach One sitting right on the edge of Mos Eisley.