High energy laser vs supervelocity missile

GTOM

I am writing a hard space opera. I plan multiple types of space battles, orbital, asteroid mine capture, board a ship (yes it is very hard to match its course). But my biggest question is the situation of convoy attack. In this case, attack frigates can speed up to 100 km/s.
How could lasers deal with so fast missiles?
(Tech specs: reactor of 100 ton ship can provide a few hundred MW, so they can maintain miliGs acceleration. X-ray lasers can make MJ pulses. Efficient against self repair armor at a range about 1000km. As far as i know the bottleneck of high energy lasers are the heat stress and deformation of focusing equipment.)
If a beam simply take out a missile, the hit of shrapnels can be still fatal. Based on molar heat capacity, i calculated it needs a MJ to melt 1kg titanium. I read this:
So if my calculations are right, 1941 Kelvin (the melting/boiling heat for titan) means atoms move at average 30m/s. If all the vapor hit the ship, and deliver GJ energy, it is still pretty bad. On the other hand a short pulse most likely dont melt it all, but rather turns a smaller part into hot gas. An MJ explosion can give a kg mass such speed (around 1 km/s), that it miss the ship. But i guess the result is somewhat between this two extremes.

So how should i describe, imagine that situation?

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Ryan_m_b

Staff Emeritus
A dead missile can’t manoeuvre. You move out of its way to nullify the threat. In this case the craft has ten seconds to shift itself which it could do with a low ISP, high thrust propulsion system.

How did you calculate that a megajoule x-ray laser would only be effective out to 1000km? The shorter the wavelength the less a beam will diverge. Can’t find it at the moment but I made a spreadsheet a few years ago to help someone with a setting that calculates beam divergence. Even soft X-rays stay relatively focused over many light seconds IIRC.

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GTOM

A dead missile can’t manoeuvre. You move out of its way to nullify the threat. I’m this case the craft has ten seconds to shift itself which it could do with a low ISP, high thrust propulsion system.

How did you calculate that a megajoule x-ray laser would only be effective out to 1000km? The shorter the wavelength the less a beam will diverge. Can’t find it at the moment but I made a spreadsheet a few years ago to help someone with a setting that calculates beam divergence. Even soft X-rays stay relatively focused over many light seconds IIRC.

I have this, that says high energy lasers put lots of stress to focusing equipment, and at this point hours of cooldown required.
So it looks like to me at this point, either rate of fire, either focusing accuracy will suffer from thermal effects.

Also while X-rays cant be efficiently reflected, but diffraction still affects them, so the frigate can get closer than light-seconds with the help of a prism shield in front of it. And it can launch a hundred missiles, so it is not guaranteed, that at least shrapnels cant get close.

essenmein

I think your scales are a bit off, xray laser with MJ pulses? doesn't sound particularly powerful as a spaceship gun. The M68 105mm (M1 Abrams main gun) sabot round has about 6MJ kinetic energy...

GTOM

I think your scales are a bit off, xray laser with MJ pulses? doesn't sound particularly powerful as a spaceship gun. The M68 105mm (M1 Abrams main gun) sabot round has about 6MJ kinetic energy...
I dont see how it is a problem. Yes, light pulses are less powerful than kinetics, but has other advantages.

Ok i dont have any exact data about how lasers are limited by the heat stress of focusing stuff. But i think it is reasonable to suppose that they wont be able to deliver the full output of the reactor.

essenmein

I dont see how it is a problem. Yes, light pulses are less powerful than kinetics, but has other advantages.
Well what would happen to your spaceships if someone were to take a M1 Abrams into orbit and shoot one of its 105mm sabots at you?

If the answer is "not much", you might want to talk about GJ or TJ laser pulses, if the answer is big hole and dead crew then why bother with the complexity of xray lasers when a late 50's artillery piece is enough?

GTOM

Well what would happen to your spaceships if someone were to take a M1 Abrams into orbit and shoot one of its 105mm sabots at you?

If the answer is "not much", you might want to talk about GJ or TJ laser pulses, if the answer is big hole and dead crew then why bother with the complexity of xray lasers when a late 50's artillery piece is enough?
The point is that thanks to the lasers, that shell dont have any chance to reach the target. Group of 100 km/s missiles have in deep space or group of 10km/s missiles in orbital combat.

essenmein

The point is that thanks to the lasers, that shell dont have any chance to reach the target. Group of 100 km/s missiles have in deep space or group of 10km/s missiles in orbital combat.
I think you're missing the point, the destructive power of the sabot is the energy it imparts on the target, just like the laser, if the energy of the laser is the same as the sabot, then more or less the capacity to damage the target is about the same.

Then you ought to wrap some numbers around the things you are describing!

The aforementioned 105mm sabot has a muzzle velocity of 1500ms-1 and a weight of about 5.8kg, this is ~6.5MJ.
You say you have 100km/s missiles, if they were the same weight as the sabot this has about 30GJ kinetic energy.

One Tonne of TNT has an energy yield of 4.2GJ, so just a 5.8kg sabot traveling at the speed of your missiles is about 6kt weapon yeild, ie, ~1/3 Hiroshima.

If your 100km/s missiles were the size of the average cruise missile (~1500kg), then well, you're at about 1.6Mt equivalent yield, that's just the mass, no explosives needed.

essenmein

Ignoring the pesky question of how you plan on accelerating your projectiles, because if it has 1.6Mt of kinetic energy, then you had to provide that ie the launcher literally has to have the power of a decent sized nuke.

Tghu Verd

The issue with missiles and lasers in space warfare is that distances involved to get anywhere - sans Warp or FTL - are immense, so speeds need to be corresponding immense. Which means a lot of kinetic energy if you hit anything, making buckshot a much better weapon than a missile. Buckshot is lightweight, spreads over a large area to confound maneuvering tactics, and if you can pump it out quickly and at speed, no ship of any size could avoid it in any event...or concentrate enough laser power to overcome it. Buckshot is also easier to manufacturer than a missile, and takes up less space overall.

I drew on a similar concept in my 'Dust' novella: "Proscribed tech from the late 30’s, each Mauler 90 had four barrels that could vomit a million fléchettes a minute and keep that up for as long as they had power and ammunition. Their superconducting linear accelerators grabbed a six-inch cobalt dart and accelerated it to ten times the speed of sound in just under twelve feet. The next one was hot on its tail in the second barrel, and the one behind that in the third, and the one behind that in the fourth. It was an assembly line of death, and just one of these monsters would shred the pod, let alone Pinda and me."

This is set on Earth, but the concept of a superconducting mass driver that spits out a lethal spray of hard to avoid and damaging when it hits buckshot seems a more practical approach than missiles to me.

Note, if you have Warp or FTL, then the warfare component becomes pretty contrived. Unless it takes inordinate amounts of time to "charge up the capacitors", any ship can just warp their way out of trouble. So then you need fixed jump points - and whatever handwavium to explain that - or FTL tracking, or some such to maintain the pace and tension.

GTOM

The issue with missiles and lasers in space warfare is that distances involved to get anywhere - sans Warp or FTL - are immense, so speeds need to be corresponding immense. Which means a lot of kinetic energy if you hit anything, making buckshot a much better weapon than a missile. Buckshot is lightweight, spreads over a large area to confound maneuvering tactics, and if you can pump it out quickly and at speed, no ship of any size could avoid it in any event...or concentrate enough laser power to overcome it. Buckshot is also easier to manufacturer than a missile, and takes up less space overall.

I drew on a similar concept in my 'Dust' novella: "Proscribed tech from the late 30’s, each Mauler 90 had four barrels that could vomit a million fléchettes a minute and keep that up for as long as they had power and ammunition. Their superconducting linear accelerators grabbed a six-inch cobalt dart and accelerated it to ten times the speed of sound in just under twelve feet. The next one was hot on its tail in the second barrel, and the one behind that in the third, and the one behind that in the fourth. It was an assembly line of death, and just one of these monsters would shred the pod, let alone Pinda and me."

This is set on Earth, but the concept of a superconducting mass driver that spits out a lethal spray of hard to avoid and damaging when it hits buckshot seems a more practical approach than missiles to me.

Note, if you have Warp or FTL, then the warfare component becomes pretty contrived. Unless it takes inordinate amounts of time to "charge up the capacitors", any ship can just warp their way out of trouble. So then you need fixed jump points - and whatever handwavium to explain that - or FTL tracking, or some such to maintain the pace and tension.
In my first universe no hyperjumps. I focus on the warlords of asteroid and orbital combat, so speed is at max 100-200 km/s. 10-20 km/s in orbital.
Once the missile is destroyed it is buckshot. But a missile has a superior range. Theoretically interplanetary range, although ships can easily evade at least one wave of missiles, and targeting human colonies is a warcrime. Since mutual destruction capability exists, i describe that even totalitarian Mercury Monarchy dont use nukes against an asteroid fortress.

GTOM

The issue with missiles and lasers in space warfare is that distances involved to get anywhere - sans Warp or FTL - are immense, so speeds need to be corresponding immense. Which means a lot of kinetic energy if you hit anything, making buckshot a much better weapon than a missile. Buckshot is lightweight, spreads over a large area to confound maneuvering tactics, and if you can pump it out quickly and at speed, no ship of any size could avoid it in any event...or concentrate enough laser power to overcome it. Buckshot is also easier to manufacturer than a missile, and takes up less space overall.

I drew on a similar concept in my 'Dust' novella: "Proscribed tech from the late 30’s, each Mauler 90 had four barrels that could vomit a million fléchettes a minute and keep that up for as long as they had power and ammunition. Their superconducting linear accelerators grabbed a six-inch cobalt dart and accelerated it to ten times the speed of sound in just under twelve feet. The next one was hot on its tail in the second barrel, and the one behind that in the third, and the one behind that in the fourth. It was an assembly line of death, and just one of these monsters would shred the pod, let alone Pinda and me."

This is set on Earth, but the concept of a superconducting mass driver that spits out a lethal spray of hard to avoid and damaging when it hits buckshot seems a more practical approach than missiles to me.

Note, if you have Warp or FTL, then the warfare component becomes pretty contrived. Unless it takes inordinate amounts of time to "charge up the capacitors", any ship can just warp their way out of trouble. So then you need fixed jump points - and whatever handwavium to explain that - or FTL tracking, or some such to maintain the pace and tension.
In my second universe warp jumps exists but if they warp anytime near a planet, gravity well destroys the ship. Battleships and orbital fighters fight regularly, motherships can jump away multiple times, the fights at the end will involve a bit magic and lovecraftian stuff.

GTOM

Ignoring the pesky question of how you plan on accelerating your projectiles, because if it has 1.6Mt of kinetic energy, then you had to provide that ie the launcher literally has to have the power of a decent sized nuke.
The point is that the ship accelerates the missiles. Their own delta-V is at most 10 km/s.
You need really high speed to get through laser defences. And missiles cant be just dodged.

Otherwise my main question were how to describe properly the interaction of shell and laser? The shell is melted than vapor can still cause a significant damage? The shell is redirected due to the explosion? Part is turned to hot gas, molten metal spreads out, solid part is misdirected a bit?
Should ships have shields in front of them so in the last second they can misdirect vapor?

some bloke

One thing to consider with physical projectiles (using kinetic energy and not a warhead or laser) is it will be the relative speed between the projectile and the target to consider.

EG, if you fire a missile at 100km/s, at a target doing 80km/s, the impact can be anywhere between 20km/s and 180km/s, depending on the angle of the targets trajectory - if it flies into the missile, it will have a larger impact than if it is flying away.

I have no idea what effect the targets speed would have on a laser's damage. Presumably a target moving away would be hit by a laser which, by their perspective, has been shifted by the Doppler effect and so would receive less energy per second than if they were to fly towards the laser. But no doubt, by the time this would have any discernible effect, there will be all sorts of relativistic things to take into account as well.

Provided that a laser doesn't need to spend long on a target to damage it, a laser which was "drawing a circle" (rotating, but with a small angle, so that the "tip" of the laser describes a circle) then it will emulate buckshot to some degree, by targeting a larger area.

essenmein

The point is that the ship accelerates the missiles. Their own delta-V is at most 10 km/s.
You need really high speed to get through laser defences. And missiles cant be just dodged.

Otherwise my main question were how to describe properly the interaction of shell and laser? The shell is melted than vapor can still cause a significant damage? The shell is redirected due to the explosion? Part is turned to hot gas, molten metal spreads out, solid part is misdirected a bit?
Should ships have shields in front of them so in the last second they can misdirect vapor?
Ok but the energy has to come from somewhere, you say a 100ton ship has a few hundred MW, lets round that up to 300MW. If 100% of that reactor output (300MJ/s) is purely used to "charge" the kinetic energy of say a cruise missile sized weapon to 100km/s, your 300MW plant would take about 7 hours to provide that energy ignoring any conversion efficiencies.

Regarding shell/laser interaction, I'm no astrophysicist so take this with grain of salt!

The first thing we can agree on I hope is that there is no air or stuff in space, so we can ignore friction.

So the kinetic energy of a projectile is in the mass, regardless of the state of matter, so a solid shell, a molten shell, a gaseous shell, traveling at the same speed all have the same kinetic energy, just take up differing volumes.

Then I would assume the laser itself is not going to have a significant effect on the trajectory, so all you're left with is the particles emitted from the shell by ablation or what ever. Since the kinetic energy alone of the weapon is Mt yeild nuke level, a chemical explosive war head is likely totally pointless, this also means exploding the shell is not going to do much but turn it from a bullet into scatter shot that's still going to feel like a 1.6Mt nuke when it hits.

So if you consider the scales involved, a 1500kg missile at 100km/s has 7.5TJ of kinetic energy, so to stop it, you need to absorb that huge amount of energy, at best your lasers or defenses are going to give it the gentlest of gentlest nudges and a slight change of course.

Rive

So if you consider the scales involved, a 1500kg missile at 100km/s has 7.5TJ of kinetic energy, so to stop it, you need to absorb that huge amount of energy, at best your lasers or defenses are going to give it the gentlest of gentlest nudges and a slight change of course.
Maybe worth considering how would weapon designers react to such countermeasures. What comes to my mind is:
- designed fragmentation to prevent easy deflection: either MIRV -like build or debris field utilized as shield against laser deflection
- deltaV budget to adjust aim at late phase

essenmein

Maybe worth considering how would weapon designers react to such countermeasures. What comes to my mind is:
- designed fragmentation to prevent easy deflection: either MIRV -like build or debris field utilized as shield against laser deflection
- deltaV budget to adjust aim at late phase
IMO the only semi plausible counter measures to high vel mass rounds is anti matter flak, ie turn the mass of the incoming projectile into energy away from you in the safety of space.

GTOM

Ok but the energy has to come from somewhere, you say a 100ton ship has a few hundred MW, lets round that up to 300MW. If 100% of that reactor output (300MJ/s) is purely used to "charge" the kinetic energy of say a cruise missile sized weapon to 100km/s, your 300MW plant would take about 7 hours to provide that energy ignoring any conversion efficiencies.

Regarding shell/laser interaction, I'm no astrophysicist so take this with grain of salt!

The first thing we can agree on I hope is that there is no air or stuff in space, so we can ignore friction.

So the kinetic energy of a projectile is in the mass, regardless of the state of matter, so a solid shell, a molten shell, a gaseous shell, traveling at the same speed all have the same kinetic energy, just take up differing volumes.

Then I would assume the laser itself is not going to have a significant effect on the trajectory, so all you're left with is the particles emitted from the shell by ablation or what ever. Since the kinetic energy alone of the weapon is Mt yeild nuke level, a chemical explosive war head is likely totally pointless, this also means exploding the shell is not going to do much but turn it from a bullet into scatter shot that's still going to feel like a 1.6Mt nuke when it hits.

So if you consider the scales involved, a 1500kg missile at 100km/s has 7.5TJ of kinetic energy, so to stop it, you need to absorb that huge amount of energy, at best your lasers or defenses are going to give it the gentlest of gentlest nudges and a slight change of course.
The point is frigates attack the convoy, they have days, weeks to speed up, till closing speed is 100km/s.

If missiles break up at a thousand kilometers, even if they have TJ energy, only a small part of it reach the ship.
Besides if they are vaporized, the frontal shield of the ship can take around GJ energy. (That melts a ton titan, so the shield is gone, but the ship is saved.)

essenmein

The point is frigates attack the convoy, they have days, weeks to speed up, till closing speed is 100km/s.

If missiles break up at a thousand kilometers, even if they have TJ energy, only a small part of it reach the ship.
Besides if they are vaporized, the frontal shield of the ship can take around GJ energy. (That melts a ton titan, so the shield is gone, but the ship is saved.)
Sure you can make those numbers sort of work, keep in mind if it takes you weeks to get up to speed, it will take the same time to stop. Then at 100km/s if your engagement area is say 1000km across, you have about 10 seconds of "fighting", and it'll take you a couple of weeks to a month to turn around and come back in case you missed...

GTOM

Sure you can make those numbers sort of work, keep in mind if it takes you weeks to get up to speed, it will take the same time to stop. Then at 100km/s if your engagement area is say 1000km across, you have about 10 seconds of "fighting", and it'll take you a couple of weeks to a month to turn around and come back in case you missed...
Long mission times are inevitable without warp drives.
Although in my story, ships usually dont turn back but land on another celestial.

Although now i really wonder about scales, maybe 1000 km is really too low.
There could be 100.000 and other limitations on lasers. Like they require frequent repairs due to degradation of focusing apparatus.

essenmein

Long mission times are inevitable without warp drives.
Although in my story, ships usually dont turn back but land on another celestial.

Although now i really wonder about scales, maybe 1000 km is really too low.
There could be 100.000 and other limitations on lasers. Like they require frequent repairs due to degradation of focusing apparatus.
If the laser focus system is really that predictably wearing out, then the weapon designers probably thought about that, you'd be swapping focus modules like you used to have to swap barrels on machine guns.

Tghu Verd

In my second universe warp jumps exists but if they warp anytime near a planet, gravity well destroys the ship.
I like this concept, used it in my novel "Guardian" where a misplaced wormhole was catastrophic!

Now, I am assuming you don't have AG in either universe? So ships free fall most of the way when traversing the solar system. In that case, your missile/laser system runs into another tricky aspect, which is the limitations on delta vee that the passengers can endure. (There is also the energy needed for maneuvers, which turns out to be a lot for even a relatively small ship.)

This pretty much means that your ships have to run the gauntlet of the missile attack, and honestly, I can't conceive a material that matches your level of tech that is going to act as a shield against even one of those monsters coming in at 100km/s. A 500 kg missile packs around 2,500,000 MJ of punch at that speed, and your missiles are likely to be more massive to get up to 100 km/s in the first place and then jink around as they reach their targets.

The other aspect worth considering is that the missiles need guidance. It can't be passive/visual: space is too dark and the speeds too great for any accuracy. Which means some type of active guidance, such as laser or radar. Which opens the door to countermeasures, which the ships would be doing with a vengeance. That might be a neat twist to balance the odds in favor of the ships, because without some advantage, the economics of losing multiple massively expensive craft and trained crews with every fight - or every flight, are these nations at war or is this some kind of pirate action going on? - means nobody is going to bother going anywhere.

GTOM

If the laser focus system is really that predictably wearing out, then the weapon designers probably thought about that, you'd be swapping focus modules like you used to have to swap barrels on machine guns.
Good point. Although in case of convoy attack (frigate job) if a few GJ isnt enough one is doomed anyway, either win or lose, no prolonged fight, no new mission until landing.
Battleships and motherships are prepared for siege.

GTOM

I like this concept, used it in my novel "Guardian" where a misplaced wormhole was catastrophic!

Now, I am assuming you don't have AG in either universe? So ships free fall most of the way when traversing the solar system. In that case, your missile/laser system runs into another tricky aspect, which is the limitations on delta vee that the passengers can endure. (There is also the energy needed for maneuvers, which turns out to be a lot for even a relatively small ship.)

This pretty much means that your ships have to run the gauntlet of the missile attack, and honestly, I can't conceive a material that matches your level of tech that is going to act as a shield against even one of those monsters coming in at 100km/s. A 500 kg missile packs around 2,500,000 MJ of punch at that speed, and your missiles are likely to be more massive to get up to 100 km/s in the first place and then jink around as they reach their targets.

The other aspect worth considering is that the missiles need guidance. It can't be passive/visual: space is too dark and the speeds too great for any accuracy. Which means some type of active guidance, such as laser or radar. Which opens the door to countermeasures, which the ships would be doing with a vengeance. That might be a neat twist to balance the odds in favor of the ships, because without some advantage, the economics of losing multiple massively expensive craft and trained crews with every fight - or every flight, are these nations at war or is this some kind of pirate action going on? - means nobody is going to bother going anywhere.
No artifical gravity, but realistic ion drives maintain miliGs.

Think about it, maybe if the long range missiles arent enough, the ships rather avoid and spare each other, to avoid mutual doom due to each others shrapnels?

I think active rockets and missiles are pretty visible in IR, not as if the ships lasers would have much problem with illuminating the targets.

At first, the warlords of the asteroid belt and pirates fight each other.
Later, there will be interplanetary war between Earth, Mercury, belt, martian rebels. That end with signing the independence of every planet .

Situations included: use interplanetary bombardment and fleets to try overcome Mercurys gigalasers and fleets and missiles.
Capture asteroid fortress (no nukes)
Level Fort Olympos on Mars with 100km/s bombs after rebels captured it.
Use orbital fighters when it is possible to take advantage of horizont, cover and hiding. (So near to celestials)

BWV

GTOM,

No offense, but if you are going to write a book maybe invest some more time in grammar and crafting good sentences? You can think out all the space tech you like, but if your book reads like your posts it will be a disaster.

"High energy laser vs supervelocity missile"

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