Commentary on Spock v. Thanatos

[Mr. Oragahn]

For the record, Aden M. Allen figured out that one of the two explosions released 450 gigajoules of energy, based on the fireball's expansion and after verification of possible energy release by the Jet A's fuel.

[Jedi Master Spock]

For the record, Aden M. Allen figured out that one of the two explosions released 450 gigajoules of energy, based on the fireball's expansion and after verification of possible energy release by the Jet A's fuel.

My apologies for the decimal slip. Good catch there.

It does serve to emphasize my point, though. Just because there are some structures still standing does not mean hundred-gigajoule to terajoule range weaponry is absent.

[Mr. Oragahn]

Probably yes, and I'm still amazed by the figure obtained there. Of course, it's nowhere a mini-nuke in terms of power, so even if the fireball sort of agrees, the other effects are largely absent. In fact, the figure seems to indicate that a lesser power for a same energy yield, like half a kiloton, will produce fireballs of roughly same dimensions, the difference of power explaining the lack of certain effects like a greater blast, and in the case of the nuke in particular, the release of many types of radiation.

Now, this is an interesting debate, although I know very little of both sides.

May I suggest you do a synthesis of the quotes and your comments on them?
It's getting very hard to keep track of everything, especially when in my case, I know very little about the units, the squad formation, names, classes, weapon types and all that jazz. Sometimes it gets so messy it's hard to know if when one mentions a shell, it's a reference to a real life ordnance type, or a fictional weapon.

Would it be possible to do something a bit more condensed?

[Jedi Master Spock]

May I suggest you do a synthesis of the quotes and your comments on them?

Would it be possible to do something a bit more condensed?

I can try. Quotes that PainRack or I have brought up since he came over to this thread:

A heavy laser or PPC can thus create more waste heat than energy going into the target.

Line from the Tech Manual which I've used to support rough energy parity between energy weapon waste heat and yield.

BattleMechs that start their movement or pass through molten magma during a Movement Phase take 2d6 points of damage to each exposed location upon entering the magma.

This came up because PainRack claimed that lava only changed the heat scale, rather than causing actual damage. Obviously, that was the end of that claim.

We could take it further by examining conduction. If we have a 1000 degree gap across 2 cm of steel between the magma and the interior of the BattleMech, we'd expect to see around... oh... close to 10^7 W/m^2. So if you have a ten second exposure of half the BattleMech, that is within the game mechanic about 4x10^9 J, or about what I'm saying should be four points of heat/thermal damage.

That may sound a little short, but this is well within range of variation on the parameters. For diamond, it would be 8x10^10 J - eighty points of damage. So the actual values of (on average) 14 damage for a half-submerged BattleMech, or 77 for a completely submerged BattleMech (that would be 8-160 GJ per the above parameter).

We've also discussed the by-now-famous Aung house PPC fringe effect quote:

What cut off her words was a bolt of blue fire hitting the ground in front of the Aung house, the blue fire momentarily blanking Cassie's vision. Through great maroon clouds of afterimage, she saw the big front window shimmer and simple melt away, felt a rush of heat on her face like the hot breath of air when she squatted too near while her mother slid her baking in and out of the oven... In the Aung yard, men were on fire.... The burning men had fallen to the ground. The whole Aung house was ablaze with flames.

PainRack has provided a variety of inaccurate descriptions of this quote; I've talked about the yield required to melt glass at a distance, which tends to push PPC yield towards the 100-GJ range, and is difficult to push below 10 GJ by any means. I consider this a high-end example.
Following continued inaccurate descriptions of the event by PainRack, I provided more detail on the latter part of the incident:

Cassie uttered a shriek that seemed to tear the lining out of her throat. Dropping her bear, she broke from her mother's arms and ran out the front door. The burning men had fallen to the ground. The whole front of the Aung house was in flames. Next to Cassie the fallen tree was ablaze with popping sounds.

PainRack then began providing quotes:

On the morning of March 22 the foggy air around the station was abruptly filled with a seemingly endless barrage of missiles and PPC fire. The attackers gave no warning and hit with such ferocity that more than 132 civilians in the surrounding buildings also died. No ComStar personnel survived the attack that left the HPG facility a pile of scorched rubble and cinders

I've pointed out this is perfectly compatible with my models.

On the battlefield northeast of Bagera, the effects were a little more dramatic. The Gauss slug, accelerated to incredible velocities, slammed into the red-brown mud with the force of a hundred conventional artillery shells. Less than a second later the PPC discharge savaged the Jaguars' position, flashing the muddy ground into dirty steam.
Colonel Timothy Price, Marshal Bryan's second in command, watched in horrified fascination as the energy released by the blast shattered the Clan 'Mechs unfortunate enough to be near the naval fire's impact point. Though the fire mission had fallen over one hundred meters to the west of Price's designated target, the effect on the Jaguars was nothing less than appalling. Nine of the lighter enemy 'Mechs just ceased to exist, blown to pieces by the unbe¬lievable energies delivered by the Fire Fang's weapons. Any Elemental unlucky enough to be caught in the primary blast area was vaporized. Most of the surviving Clan forces were so badly dam¬aged as to be useless as fighting machines, or even as spare parts.

Comparing to this, a modern artillery shell strikes with around 1/20th the force I ascribe to a mech-grade gauss rifle, which would put a naval gauss rifle at around 200x the force. Well within the precision of the description.

I estimate from the description of the PPC strike in this passage that the yield of a naval PPC is in fact 100-1000 GJ, which - since we're looking at a factor of ten between naval and mech weapons - precisely matches the Aung house incident.

Apparently sensing imminent defeat, the Blakist Fleet commander ordered an orbital bombardment in and around Harlech after nearly a week of fighting. Simultaneously, the Blakist sterilized the entire Remus continent using stragetic nuclear weapons.

This, I dismissed as being largely irrelevant. We know what nukes do already.

As I write this, Harlech burns. The majestic spires of Wolf Hall, once strong and proud on the skyline, are blackened and broken. Now they arenothing but a grave marker for the fallen Dragoons. Choked with oil and debris, Lake Kearney is a black pit that devours light and reflects nothing. The Harlech Links(whhere I have spent so many pleasant hours over the years) is a blasted heath gouged with BattleMech footprints.
In the streets, once filled with cosmopolitan bustle, only the dead now linger. The sky is black with smoke from a thousand fires. They rage unchecked, for tto venture out invites attack from the white BattleMechs and packs of battle armor that stalk the streets firing at any movement. The wounded fill the hospitals, but are not safe even there from infantry searching for mercenaries or their families.
During the night(or what the chronometers tell me was night), the fighting came a lot closer to the HPG. I only have a Level II of infantry to defend the transmitter. I hope we can hang on. I hope the remainding Dragoons can defeat those who were once my brothers.
I hope Precentor Martial Steiner-Davion can save us all from these monsters.
I don't know how much longer I'll be able to keep transmitting...

This, I've said is compatible with even low-kiloton range bombardments, but very much compatible with the 100-1000 GJ range naval weapons that I've been talking about.

but the first spotting rounds dropped short by more than a hundred meters, landing in the streets adjacent to the spaceport.One 125-millimeter shell crashed through the roof of a warehouse that held drums of high grade petroleum

I've talked about this as nothing strange for accuracy of a ballistic weapon, period.

Quintus pointed to the hole burned through at the man's ribs. "Had to be a laser rifle. Clean shot."

Dan nodded slowly. "From the angle, the shot must have gotten both lungs and heart. No blood, though. The beam cauterized everything."

Two hot red laser bolts leaped from Craon's pistol after the other fleeing Liao operative. The first missed and exploded a wooden post into a storm of flaming splinters.

The Star Colonel twisted and slid down in the hatch of his tank, half his head burned away.

Discussion of laser infantry weapons. IMO, fits perfectly with the low-megajoule range that I've suggested for them. Incidentally matches WH40K lasgun descriptions quite well.

The 20mm Gatling gun is a time-proven weapon, giving the Scorpion good defensive firepower with plenty of punch. Though some users of the tank have tried 30mm machine guns, the Gatling gun’s high rate of fire makes larger shells unnecessary.

The Mithras’s turret-mounted Series 2b autocannon allows accurate, sustained fire against targets up to one thousand meters from the vehicle. The system’s advanced autoloader allows the gunner to select a variable rate of fire, and at full speed the 50mm cannon can fire twelve rounds a minute

I've said we don't have enough information to really say which conventional guns have more or less kinetic energy, or what combination of velocity, caliber, mass, and explosive warhead. Not really an interesting discussion - PainRack has been claiming inconsistency (and therefore inability to determine squat about anything kinetic) while I've been claiming information is very limited (and therefore, we can only say a few things about autocannon specifically).

A lance of ruby energy fell down from the skies like the glare of some angry god, scorching the earth and leaving a scar along the ground and across a Com Guard jump capable Kanga hovercraft. It split open under the naval-class laserfire, engine erupting in a brilliant fireball that quickly burned off into a dark, oily cloud. Its heavy ammunition stores detonated in sympathetic explosions, shredding armor and hurling large chunks of the vehicle up to a quarter-kilometer distant.

The Sixth Crucis Lancers lost two BattleMechs in quick succession as well as a squad of Infiltrator battle armor, who were burned down to a tortured composite of half-melted armor, crisped flesh, and ash.

Already, the probing lasers searched for their next victim, found it in another NAIS cadet. The laserfire took an arm from his Watchman. It might have cut the MEch down its entire lenght but for the Watchman's speed and the lightning reactions of the cadet, who jerked his machine mostly out of the beam's path.

Some naval laser fire. I've remarked that the most interesting part of this entire sequence is the explosion of the Kanga.

[Mr. Oragahn]

Quickly, here, some details:

M256 120mm Smoothbore Gun
The gun tube, breech, and piston recoil approximately 11 inches (279 mm) during firing. The gun recoils about 1.5 inches (38 mm) before the projectile leaves the gun tube.

[Jedi Master Spock]

Quickly, here, some details:

M256 120mm Smoothbore Gun
The gun tube, breech, and piston recoil approximately 11 inches (279 mm) during firing. The gun recoils about 1.5 inches (38 mm) before the projectile leaves the gun tube.

Well, I'll give you some sample calculations, but that doesn't actually bring us anywhere new. The barrel has a mass of 1190 kg. The M829A2 has a 8.7 kg propellant charge, a 7.9 kg projectile, and a muzzle velocity of 1680 m/s. Assume, momentarily, that all momentum is first transferred to the gun barrel itself.

Assume the net forward velocity of hot gases is distributed uniformly from 0 m/s (sideways) to 1680 m/s (forwards). The total forward momentum of gases and shell is then about 21,000 kg m/s, or enough to accelerate the barrel to 17.3 m/s, with a kinetic energy of 180,000 joules. Braking over 279mm would give a braking force of 640 kN, or in imperial units, 72 tons of force (some rounding is involved with these figures).

You'll note that Thanatos actually gave a figure of "56 tonnes" of recoil for the M256 in our debate. The difference in our figures is entirely understandable for several reasons, and doesn't mean that he's wrong; first, in the calculations above, I've assumed all momentum is first transferred to the barrel before going to other parts; in the first 38mm of braking, the barrel hasn't yet accelerated to full speed, and so you actually get a little better mileage out of your brakes, since the momentum/energy ratio is higher, and the piston and breech may not be counted in the barrel mass. Perhaps also importantly, a tonne and a ton differ by about 10%; the former is larger.

This doesn't actually change the core issues that I pointed out; the Conqueror barrel is 2.49m, while the M256 is 6.6m. This means that the Conqueror barrel is likely lighter weight - if the recoiling mass is proportionate to length relative to the M256, and the recoil distance is 218mm, the force would be 3.4x as much for firing a round with the same total momentum.

What I concluded about WH40k tanks in my debate with Thanatos isn't that they were actually less powerful than modern tanks, or in all ways inferior; they simply aren't very well designed to make or resist kinetic penetration attacks.

I calculated that the discarding-sabot round of the Vanquisher tank delivers up to 2-3x the KE that an Abrams discarding-sabot round delivers; however, while it may be technically more powerful, it's a much less advanced design. It's a steel penetrator with a L/D ratio of about 3.5 (look at the illustration in Imperial Armour). Modern penetrators are usually made of tungsten or depleted uranium, and have L/D diameters an order of magnitude higher.

A similar story holds for the actual armor layouts, not that we discussed those; WH40k vehicles are generally built like they rolled off the field in WWII. That's the design aesthetic. Thus, while they have extremely rugged frames, resist shocks and explosions well, and often make use of somewhat advanced materials (adamantium, ceramite, plasteel), they are not actually particularly sophisticated war machines in the ways that we consider important now.

The Abrams is designed to make and defeat high-energy kinetic penetrators at long range, in the hands of highly trained professionals. The Leman Russ is designed to be dropped upside-down, abused by new recruits who can't read and come from feral worlds that have barely rediscovered metal-working, put on the "missing" side of the supply line, and then expected to survive being bludgeoned repeatedly with Orkz and unsophisticated explosive charges.

(Of course, on the other end of the table, mecha have terrible armor arrangements, but BT has magic physics-violating armor that somehow transfers the shock from high-energy kinetic attacks over multiple square meters.)

[Mr. Oragahn]

I can't remember why I provided these numbers. What I know though is for equal mass, you certainly want your penetrating projectile longer than it's wider.
A short and large bore isn't really engaging when it comes to ranges. That said when we consider the melee ranges of WH40K, it's not surprising. We're almost dealing with tank melee.