Orbital bombardments, planetary defenses, Death Stars, etc.

[Marko Dash]

I don't think the republic fleet would be holding back due to logistical reasons. they're fighting in orbit of the capital, they won't be lacking for fuel or replacement parts after a battle like an outer rim fleet might.

[Eternal_Freedom]

Except a good chunk of that fleet had just come from the Outer Rim Sieges (Obi-Wan and Anakin's Open Circle Fleet IIRC). So that group at least probably were hurting for supplies and fuel having just raced across the galaxy.

[Batman]

Except they're still fighting next to Coruscant, so them going all out so they actually win still makes sense as they'd still be in a position to resupply afterwards whereas conserving their resources only makes sense if they expect to lose in which case why bother fighting to begin with?

[Eternal_Freedom]

Fair point, though those ships would still not be at full strength, so they would have less time to go all-out.

[Batman]

Absolutely. Their endurance is certainly going to be significantly below maximum. Their firepower is not for as long as they can keep it up and there's little reason for them not to use it

[Eternal_Freedom]

Very true. Though of course the droid ships would also not be at full capacity having made their own rush to Coruscant from wherever they were based, and having to keep fuel reserves to withdraw again, so I suppose it would even out. The Open Circle Fleet had enough time to arrive as reinforcements so the CIS fleet would have been fighting for hours at least.

[Ender]

Except they're still fighting next to Coruscant, so them going all out so they actually win still makes sense as they'd still be in a position to resupply afterwards whereas conserving their resources only makes sense if they expect to lose in which case why bother fighting to begin with?

You are assuming that they started their trip in at full capacity when there is no reason to, and assuming that winning will not entail giving pursuit. They have no reason to assume they will be able to fully resupply there - the speeds of FTL communication and travel means that as soon as the CIS fleet identifies the republic fleet is there, that means their forces elsewhere can attack the positions the Jedi fleet just left, which means that you get a cascading chain of reinforcement and striking. This makes the general shape of galactic warfare one of siege and logistical attrition, and would mean the foresight of the Jedi in knowing where there will be a weak spot to attack before they can counter would be a critical component of military strategy. Both of which we see in the series

And we know giving pursuit is in fact what happened - the rest of the fleet immediately left, and Anakin and Obi wan remained on Coruscant, and Obi Wan left shortly after.

Absolutely. Their endurance is certainly going to be significantly below maximum. Their firepower is not for as long as they can keep it up and there's little reason for them not to use it

Unleashing stellar scale powers both in combat and in the destruction of ships in low orbit over your capital is a really bad idea. Particularly when your objective is insertion/rescue, but in general as well.

[Sky Captain]

For example against a SiO2 target, to get the equivalent of a 1 kiloton detonation it takes 6 *10^19 joules released in 0.000756 seconds. That's faster than what it looks like a TL applies, so the math needs some more work, but basically it takes a 14 gigaton TL to approximate a 1 kiloton bomb. This isn't a linear relationship btw, a 100 ton bomb equivalent ("tbe" from here on out) is 6*10^17, 10 tbe is 10^15, when you get down to like 10 kg of tnt you are talking 10^9 tbe. So it isn't that far off from what we see. I should refine this more but I have a lot going on so I probably won't.

Not sure I understand, Why would there be so large difference to make 1 kt explosion at target you need to pump out of your energy gun 14 Gt of energy. I know some energy would go into material to flash it to plasma, but at those scales energy to flash few thousand tons of rock to plasma would be relatively minor fraction. When real world nuke explode it also flashes surrounding material into plasma to generate shockwave, warhead itself provide very little material itself. Wouldn't megaton and higher yield energy weapons cause broadly similar effect to a comparable yield nuke when used in atmosphere against ground targets?

Unleashing stellar scale powers both in combat and in the destruction of ships in low orbit over your capital is a really bad idea. Particularly when your objective is insertion/rescue, but in general as well.

Aren't Star Wars warships generally expected to survive their own heavy weapons at least for a few salvos to overcome the shielding. If so there would be no choice, but to go full power to overload enemy shields with heavy weapons. If Star Wars depicted high energy combat realistically then enemy fleet in low orbit already would be a no win situation. Unleash stellar scale firepower to take it out and say good by to your capital or surrender and let them take it relatively intact.

A real world example would be tanks fighting in a town. No way the town is going to stay intact.

[Patroklos]

Turbolasers are not beam weapons. They are not slugs either, but the observed canon instances generally show some sort of elongated sublight mass most often described as bolt. Given their relatively compactness over a beam, however, its probably a good bet they work more like slugs.

[Ender]

Not sure I understand, Why would there be so large difference to make 1 kt explosion at target you need to pump out of your energy gun 14 Gt of energy. I know some energy would go into material to flash it to plasma, but at those scales energy to flash few thousand tons of rock to plasma would be relatively minor fraction. When real world nuke explode it also flashes surrounding material into plasma to generate shockwave, warhead itself provide very little material itself. Wouldn't megaton and higher yield energy weapons cause broadly similar effect to a comparable yield nuke when used in atmosphere against ground targets?

Please read the link I included in the post. Most of the energy involved comes in getting the target material up to temperature to mirror the detonation pressure of TNT. High detonation pressure correlates with high detonation velocity, not necessarily with the explosive's total energy, and nuclear reactions have a detonation velocity orders of magnitude greater than chemical explosives.

[Ender]

Not sure I understand, Why would there be so large difference to make 1 kt explosion at target you need to pump out of your energy gun 14 Gt of energy. I know some energy would go into material to flash it to plasma, but at those scales energy to flash few thousand tons of rock to plasma would be relatively minor fraction. When real world nuke explode it also flashes surrounding material into plasma to generate shockwave, warhead itself provide very little material itself. Wouldn't megaton and higher yield energy weapons cause broadly similar effect to a comparable yield nuke when used in atmosphere against ground targets?

Please read the link I included in the post. Most of the energy involved comes in getting the target material up to temperature to mirror the detonation pressure of TNT. High detonation pressure correlates with high detonation velocity, not necessarily with the explosive's total energy, and nuclear reactions have a detonation velocity orders of magnitude greater than chemical explosives.

On reflection, Mike's explanation, while great if you have some basic grounding, isn't the most layman friendly, and I think my connections between my points 1, 2, and 3 is not as clear as it could be

so, basic idea here - how different weapons do things are mediated by immensely different physics depending on the exact weapon, giving them a very different result. The obvious example is a bullet vs a heat ray - the bullet puts a hole in things through momentum and collision physics, the heat ray by calorimetrics. Momentum, energy, power, radiation, heat, pressure, substance, all have a big role to play.

This "things are different" applies even to things that are superficially the same - just because you have two bombs with the same energy does not mean they will have the same results. Before Hiroshima, there had been multiple explosions with similar or greater energy release when ammo ships or armory depots went up. What made the nuclear bomb so shocking and at first unbelievable is that one bomb that small had done that level of devastation.

The way 1 kiloton of TNT, or energetically equivalent amounts of black powder or enriched uranium explode will similarly be very different. This is the designation that makes something a "high explosive", that the detonation velocity and detonation pressure of something like RDX are very high and good for fragmenting the target. For a nuclear bomb, consider the extremely high velocities of neutrons and the very small distance they need to go to react; the effective velocity for comparing them to a chemical reaction is absurdly high. And as I said in 4, overpressure is the most useful for bombardment so it is not surprising that SW energy weapons mirror such explosives in the real world.

Moving to the meta discussion, we are looking to match the visuals as I said in point 2. This gets a bit tricky, as CGI visuals are pretty infamous for not mirroring reality. The example that leaps to mind from the old vs days is that DS9 episode where the Kingons and Romulans bombard the fake Dominion planet, and the shockwaves ripple across the planet at completely the wrong speed. I haven't looked at Rogue 1, but I'd put easy money on the shockwave from the Death Star blast being wrong as well.

Fortunately, we have the non CGI examples to use, some from Rogue 1 but definitely from when the were doing practical effects in the OT and when they were copy-pasting explosions over greenscreen in some of the PT shots. There we know the explosions follow certain consistent physics. IIRC at Hoth the standard SFX explosions was a quarter stick of dynamite with the larger one being a few ounces of TNT (if Wayne is still around I believe he can confirm since that was his wheelhouse back in the day).

So back to the point, this means that we can handwave and say that the properties of SW energy weapons approximate the blast effects of TNT both because it makes sense and because that's what their visuals were, and do some work backwards to get a baseline for the weapon that matches those visuals. Plus if we are talking how they should be, yeah, from what we know having them mirror TNT are pretty effective. Lord knows we've killed enough folks that way.

Keep in mind it won't be a perfect match, and certainly not for all situations. Best we can do is model as many examples as possible and try to figure out a trend line through them, fudging where we must.

There are still some problems with the model - for one we are guessing at the target and fudging some of the inputs because they would be empirically derived and no one to my knowledge has tried to get some of those figures (eg heat of vaporization for granite). On top of that, at high temperatures and pressures these equations break down, and we are doing our best to set a lower limit or order of magnitude estimate. Finally, we don't know key elements, like the application time of the weapons. If a TL needs to apply 6e19 joules of energy in 0.000756 seconds to have a power of 8e22 watts to mirror a 1 kt explosion, but applies over 1 second instead, we need to ramp up the energy applied on the front end. Conversely, if the TL applies at a vastly faster rate than TNT (which wouldn't match visuals but whatever) the energy can somewhat lower.

Modeling orbital bombardment is hard.

[Sky Captain]

Please read the link I included in the post. Most of the energy involved comes in getting the target material up to temperature to mirror the detonation pressure of TNT. High detonation pressure correlates with high detonation velocity, not necessarily with the explosive's total energy, and nuclear reactions have a detonation velocity orders of magnitude greater than chemical explosives.

From the linked article I got that energy weapon that relies on vaporizing part of a target to produce 1 kg of TNT worth of explosion would need to output about 10 times the energy of 1 kg of TNT to equal it. Easier to vaporize materials would need less energy than materials with very high boiling temperatures and heat of vaporization.

A 1 kt explosion would need about 10 kt worth of energy output from energy gun if it is delivered in a similar time frame to a TNT detonation not 14 Gt.

For a nuclear bomb, consider the extremely high velocities of neutrons and the very small distance they need to go to react; the effective velocity for comparing them to a chemical reaction is absurdly high.

Wouldn't that be pretty good approximation to sci fi particle weapons. A particle canon in space fires a pulse of high energy particles containing 10 kt of energy. At the target end it should behave similar to a 10 kt nuke if pulse duration is similar to time it takes plutonium to fission in a nuke.

There are still some problems with the model - for one we are guessing at the target and fudging some of the inputs because they would be empirically derived and no one to my knowledge has tried to get some of those figures (eg heat of vaporization for granite). On top of that, at high temperatures and pressures these equations break down, and we are doing our best to set a lower limit or order of magnitude estimate. Finally, we don't know key elements, like the application time of the weapons. If a TL needs to apply 6e19 joules of energy in 0.000756 seconds to have a power of 8e22 watts to mirror a 1 kt explosion, but applies over 1 second instead, we need to ramp up the energy applied on the front end. Conversely, if the TL applies at a vastly faster rate than TNT (which wouldn't match visuals but whatever) the energy can somewhat lower.

If 6e19 J equal 4,2e12 of TNT where does the rest go? Wouldn't the remaining energy that did not go into producing shockwave in ground make a monster atmospheric firestorm setting everything within line of sight on fire causing far more destruction than simple 1 kt TNT bomb?

An atmospheric meteor explosion has longer application time then nuke yet the blast damage is similar. A Tunguska meteor explosion produced about 15 Mt of energy and toppled trees over 2000 km2 something you would expect from similar nuclear airburst.

[Formless]

(if Wayne is still around I believe he can confirm since that was his wheelhouse back in the day).

Nope, he was banned in 2009. Apparently everyone thought he had been banned prior to that, but that was when the Admins made it official.

And back to thread...

[Ender]

From the linked article I got that energy weapon that relies on vaporizing part of a target to produce 1 kg of TNT worth of explosion would need to output about 10 times the energy of 1 kg of TNT to equal it. Easier to vaporize materials would need less energy than materials with very high boiling temperatures and heat of vaporization.

A 1 kt explosion would need about 10 kt worth of energy output from energy gun if it is delivered in a similar time frame to a TNT detonation not 14 Gt.

You would be better served applying the math instead of relying on a heuristic. The worked example at the end can guide you; the ideal gas law necessitates absurdly high temperatures to get tot he pressure and that's where most of the energy goes in.

Wouldn't that be pretty good approximation to sci fi particle weapons. A particle canon in space fires a pulse of high energy particles containing 10 kt of energy. At the target end it should behave similar to a 10 kt nuke if pulse duration is similar to time it takes plutonium to fission in a nuke.

No, the models are extremely different. Neutron absorption in a specialized environment designed to facilitate fission is very different to a target being struck by a particle cannon. Chief among them is that the particles themselves aren't even the same type - neutrons vs electrons or protons

If 6e19 J equal 4,2e12 of TNT where does the rest go? Wouldn't the remaining energy that did not go into producing shockwave in ground make a monster atmospheric firestorm setting everything within line of sight on fire causing far more destruction than simple 1 kt TNT bomb?

It is going into making the shockwave. It is raising the temperature of the air to create the overpressure. How that models is an open question - my initial impulse is it should be a huge fireball emitting sterilizing amounts of gamma rays, but we don't have any equations to handle high temperature high pressure situation, as I said. Then there is the handwave of "what is a turbolaser" because neutrino radiators should be emitting lethal amounts of radiation to ship crews but aren't so...

An atmospheric meteor explosion has longer application time then nuke yet the blast damage is similar. A Tunguska meteor explosion produced about 15 Mt of energy and toppled trees over 2000 km2 something you would expect from similar nuclear airburst.

Which is a physical impactor and has a different physical model.

[KraytKing]

Isn't neutrino radiation pretty much a non-factor? I won't pretend to understand all the physics you're discussing, but this https://what-if.xkcd.com/73/ makes it fairly clear that it takes a lot of neutrinos to be lethal.

Of course, please correct me if I'm wrong.

Now, in regards to endurance, my understanding is that Star Wars ships have quite a lot of it. ICS at the least heavily implies that ship fuel stores are singularity-level densities in order to maintain tremendous power output. And for that matter, I don't think it's entirely accurate to portray Star Wars ships as having that level of firepower relative to their ability to take it. This is the only example we see of a ship going down in a single shot, barring the Death Star. It may be akin to the Hood against the Bismarck. Given firepower differences, it may be more akin to the latter hitting the magazine of an unfortunate destroyer or even torpedo boat.

[Formless]

Isn't neutrino radiation pretty much a non-factor? I won't pretend to understand all the physics you're discussing, but this https://what-if.xkcd.com/73/ makes it fairly clear that it takes a lot of neutrinos to be lethal.

Of course, please correct me if I'm wrong.

Now, in regards to endurance, my understanding is that Star Wars ships have quite a lot of it. ICS at the least heavily implies that ship fuel stores are singularity-level densities in order to maintain tremendous power output. And for that matter, I don't think it's entirely accurate to portray Star Wars ships as having that level of firepower relative to their ability to take it. This is the only example we see of a ship going down in a single shot, barring the Death Star. It may be akin to the Hood against the Bismarck. Given firepower differences, it may be more akin to the latter hitting the magazine of an unfortunate destroyer or even torpedo boat.

Atomic Rockets actually has a section on neutrino beams as a weapon. The article notes that the effectiveness of the weapon is inversely correlated with the density of the target's material composition as well as the volume of material it has to pass through. A neutrino beam fired from orbit could pass right through an astronaut floating mere meters away from the barrel and all it will do is increase their cancer risk, but if the intended target were a bunker buried deep underground and made of steel it would be fatally irradiated because of the unique way neutrinos interact with other matter. Basically, the neutrino hits the nuclei of atoms and transfers its momentum into those atoms. That sends the whole atom smashing into other atoms as secondary radiation-- kind of like a gun that shoots cosmic rays, only with infinitely better penetration. So when you fire your neutrino beam at a dense target like a planetary bunker or maybe a massive starship, you turn its own metallic superstructure into a radioactive hazard that kills the occupants and electronics. As a bonus, the usual way people think of protecting themselves against radiation is dense metallic shielding like lead or tungsten, but in the case of neutrino radiation it only makes things worse. Its a rare weapon where it will be less effective against a starship whose radiation bunker is surrounded by a large volume of water and no dense materials at all.

I've also read that such a weapon would be ideal for diffusing fission bombs as it would rapidly change the isotope of uranium or plutonium inside the warhead, rendering it useless for setting off a nuclear explosion. It wouldn't even have to emit fatal levels of neutrino radiation because fissile material is just that dense. We might even be able to make neutrino weapons that disable nukes within this century, although whether they would be practical is highly debatable.

Presumably Ender is concerned with the secondary radiation problem because Star Destroyers are mile long shells made of metal, and some sources suggest they use a denser metal than steel. And you wouldn't want to make them out of aluminum because that happens to be the worst metal available for protecting yourself against conventional radiation. According to NASA, aluminum can actually make radiation hazards worse. However he has not shown his math to sufficiently conclude this is a real problem with neutrino radiators, only a potential problem.

[Rhadamantus]

Isn't neutrino radiation pretty much a non-factor? I won't pretend to understand all the physics you're discussing, but this https://what-if.xkcd.com/73/ makes it fairly clear that it takes a lot of neutrinos to be lethal.

Of course, please correct me if I'm wrong.

Now, in regards to endurance, my understanding is that Star Wars ships have quite a lot of it. ICS at the least heavily implies that ship fuel stores are singularity-level densities in order to maintain tremendous power output. And for that matter, I don't think it's entirely accurate to portray Star Wars ships as having that level of firepower relative to their ability to take it. This is the only example we see of a ship going down in a single shot, barring the Death Star. It may be akin to the Hood against the Bismarck. Given firepower differences, it may be more akin to the latter hitting the magazine of an unfortunate destroyer or even torpedo boat.

Atomic Rockets actually has a section on neutrino beams as a weapon. The article notes that the effectiveness of the weapon is inversely correlated with the density of the target's material composition as well as the volume of material it has to pass through. A neutrino beam fired from orbit could pass right through an astronaut floating mere meters away from the barrel and all it will do is increase their cancer risk, but if the intended target were a bunker buried deep underground and made of steel it would be fatally irradiated because of the unique way neutrinos interact with other matter. Basically, the neutrino hits the nuclei of atoms and transfers its momentum into those atoms. That sends the whole atom smashing into other atoms as secondary radiation-- kind of like a gun that shoots cosmic rays, only with infinitely better penetration. So when you fire your neutrino beam at a dense target like a planetary bunker or maybe a massive starship, you turn its own metallic superstructure into a radioactive hazard that kills the occupants and electronics. As a bonus, the usual way people think of protecting themselves against radiation is dense metallic shielding like lead or tungsten, but in the case of neutrino radiation it only makes things worse. Its a rare weapon where it will be less effective against a starship whose radiation bunker is surrounded by a large volume of water and no dense materials at all.

I've also read that such a weapon would be ideal for diffusing fission bombs as it would rapidly change the isotope of uranium or plutonium inside the warhead, rendering it useless for setting off a nuclear explosion. It wouldn't even have to emit fatal levels of neutrino radiation because fissile material is just that dense. We might even be able to make neutrino weapons that disable nukes within this century, although whether they would be practical is highly debatable.

Presumably Ender is concerned with the secondary radiation problem because Star Destroyers are mile long shells made of metal, and some sources suggest they use a denser metal than steel. And you wouldn't want to make them out of aluminum because that happens to be the worst metal available for protecting yourself against conventional radiation. According to NASA, aluminum can actually make radiation hazards worse. However he has not shown his math to sufficiently conclude this is a real problem with neutrino radiators, only a potential problem.

That's a good and valid point. Also, I'm pretty sure that Ender was talking about how neutrino radiation could absolutely kill people at SW level power densities.

A 10E24W TL firing for 1 second emits 10E24J of energy. If we assume 50% of that is neutrino waste energy, we get 3E33 Neutrinos. A supernova emits 10E57 neutrinos. A fatal radiation dose would then be achieved at 60 centimeters for one blast. If the gun had a lower efficiency, or a higher power, or was fired multiple times, it could kill someone a few meters away easily.

[Formless]

That's a good and valid point. Also, I'm pretty sure that Ender was talking about how neutrino radiation could absolutely kill people at SW level power densities.

A 10E24W TL firing for 1 second emits 10E24J of energy. If we assume 50% of that is neutrino waste energy, we get 3E33 Neutrinos. A supernova emits 10E57 neutrinos. A fatal radiation dose would then be achieved at 60 centimeters for one blast. If the gun had a lower efficiency, or a higher power, or was fired multiple times, it could kill someone a few meters away easily.

Frankly, you wouldn't want to be standing that close to a conventional radiator anyway, since they are supposed to give off heat. If they used a conventional radiator and you stood right next to it during peak operation, you would cook. you also don't need to place the radiators directly on top of the weapons emplacements. The whole point of coolant lines is to transport waste heat from the machinery that's generating inefficiency to the radiators for disposal. Therefore the radiators can be placed somewhere far from the crew (remember, mile long starship-- there is plenty of room in there which no one occupies), just like on more realistic spacecraft only the radiators can go on the inside. Finally, we don't know the thermal efficiency of turbolasers, so its all speculative. I think it was Sea Skimmer who once pointed out that much of Star Wars' technology would require high energy efficiency to begin with, like, you know, the Death Star. Or even just any ship that has to be able to reach orbit from a planet, like the Falcon. So again, the theoretical problem with neutrino radiation as a mechanism for managing waste heat doesn't necessarily translate into a practical problem.

[Sky Captain]

You would be better served applying the math instead of relying on a heuristic. The worked example at the end can guide you; the ideal gas law necessitates absurdly high temperatures to get tot he pressure and that's where most of the energy goes in.

I ran the heat calculation for silica and ended up with 32 MJ/kg to heat it up to 25 000 K. Example in explosives article about iron is 49.3 MJ/kg to simulate 1 kg of RDX exploding so it is close enough. 1 kt would therefore need about 3.2e13 J delivered from energy weapon shot into silica target. How did you get 6e19 J for 1 kt?

It is going into making the shockwave. It is raising the temperature of the air to create the overpressure. How that models is an open question - my initial impulse is it should be a huge fireball emitting sterilizing amounts of gamma rays, but we don't have any equations to handle high temperature high pressure situation, as I said.

So bombardment with energy weapons would kinda resemble Boiling liquid expanding vapor explosion? Lots of heat and thermal radiation, but less destructive shock wave?

[Galvatron]

[Formless]

Generation Tech isn't exactly a reliable source of canon information; they frequently not only mix Disney and Legends canon in their arguments, but in their video about star dreadnoughts I think they straight up copy-pasted parts of fractalsponge1's fanon about the origins of many of his designs in-universe. Information which, I remind you, was not canon even when Lucasfilm canonized fractalsponge1's dreadnought designs. That video likewise seems to have a ton of their own fanon and headcanon mixed in with argument and legends canon presented alongside Disney's canon. Its interesting to think about, but not definitive in any way.

[Galvatron]

Oh, I agree. Still, it's not a topic that's commonly addressed on YouTube. He also completely neglected to mention planetary defense cannons as an obvious deterrent against capital ship bombardments.

[Galvatron]

In case anyone still cares: the new edition of what used to be known as the ICS has stripped out a lot of the numerical specs from the Acclamator data file, including the 200-gigaton yield for its turbolasers.

Spoiler

[Eternal_Freedom]

It does still refer to a BDZ though, meaning the ability to do that with Acclamators is canon again.

[chimericoncogene]

The ROTS version also keeps the Moment Magnitude scale earthquake medium turbolaser and ice moon melting prow gun of the Munificent.