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:
https://sciencing.com/calculate-velocity-temperature-6234001.htmlSo 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 don't 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?

 

[Ryan_m_b]

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.

 

[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.

https://en.wikipedia.org/wiki/National_Ignition_Facility#Driver_laser
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 can't 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 can't 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 don't see how it is a problem. Yes, light pulses are less powerful than kinetics, but has other advantages.

Ok i don't 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 won't be able to deliver the full output of the reactor.

 

[essenmein]

I don't 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 don't 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 don't 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.

 

[member 656954]

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 don't 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 can't 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 can't 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, let's 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, let's 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 don't 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 don't 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.

 

[member 656954]

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 isn't 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.

 

[GTOM]

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.

I find it offensive, since english isn't my mother language. Otherwise i don't see errors except i tend to use terms like Mercurys instead of something of Mercury.

 

[BWV]

Why be offended if English isn’t your native language? English is hard. Are you writing your book in another language? Your posts are understandable, but full of awkward phrasing and grammatical errors. Writing quality English prose is far more difficult than imagining cool spaceship technologies.

 

[GTOM]

Of course i write stories in mother language...

 

[BWV]

And take it as a complement that it was not apparent that you are not a native English speaker, your writing is conversational and in line with what I have seen from American high school or college graduates

 

[hutchphd]

I have a very minor complaint.

Also while X-rays can't 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.

A prism does not use diffraction to work but rather it relies on dispersion: not so good for xray . Probably an effective xray shield would not be called a prism. However many atomic crystals do diffract x-rays the way a periodic "diffraction grating" does for light. Just FYI!

 

[GTOM]

I have a very minor complaint.

A prism does not use diffraction to work but rather it relies on dispersion: not so good for xray . Probably an effective xray shield would not be called a prism. However many atomic crystals do diffract x-rays the way a periodic "diffraction grating" does for light. Just FYI!

Ok, thank you.

 

[GTOM]

Although i wondered at 100.000 km, there is considerable amount of light lag. A small missile can maintain 1m/s2 for 1000 sec and avoid a good hit. Maybe frigate and destroyer lasers should be rather configured to hit ten targets in a sec below 10.000 km.
(Numbers: 100 ton warship carries 10 ton missiles, 1000 of 10kg warhead. With 100 km/s each has an energy of 50GJ. With 30 m/s spread of vapor - if they melted - they can still take out a ship from a few hundred km. A booster phase with 1km/s sets the warheads to collusion course)
Fighter lasers could be configured for a dozen target at 1000 km, the siege laser of a battleship could take out something at 100.000 km.

(Dedicated roles. Frigate : convoy attack, Destroyer : convoy defence, fighter : convoy defence if arent enough destroyers and orbital/cover based combat attack, battleship : siege, mothership : mobile base)

 

[member 656954]

I think you're best off ignoring the practical physics for your story and just get on with writing compelling, engaging battle sequences. Because unless everything is powered by an antimatter Em drive*, you just can't get chemical rockets to those speeds in a reasonable time-frame, and missiles likely never, they won't have enough fuel.

* Yes, I know the Em drive is not real

 

[GTOM]

I think you're best off ignoring the practical physics for your story and just get on with writing compelling, engaging battle sequences. Because unless everything is powered by an antimatter Em drive*, you just can't get chemical rockets to those speeds in a reasonable time-frame, and missiles likely never, they won't have enough fuel.

* Yes, I know the Em drive is not real

The point is that make realistic space battles unique, that the frigate speeds up for weeks. Then it launches kinetics.

(Otherwise i think the exhaust of fighters and mass drivers can also speed up projectiles to 10 km/s and i also show big railgun towers speed up small missiles to 100 km/s for interplanetary siege)

 

[member 656954]

Not sure if I am interpreting what you write as you intend, but 'unique' space battles will be hard.

Warfare of this kind has been written up many times before - with kinetics, with missiles, with lasers, with icebergs as shields, taking into account light lag, ignoring light lag - and while it is interesting to understand the mechanics of the science driving the battles, what is more interesting is how your characters react.

If you can write emotive, engaging prose, then all the nitty gritty details can be described in a few sentences and your readers will fill in the gaps. If you can connect with them emotionally, sparse technical details will be forgiven. If you can't, then all the physics in the world won't make your novel a winner.

 

[GTOM]

Not sure if I am interpreting what you write as you intend, but 'unique' space battles will be hard.

Warfare of this kind has been written up many times before - with kinetics, with missiles, with lasers, with icebergs as shields, taking into account light lag, ignoring light lag - and while it is interesting to understand the mechanics of the science driving the battles, what is more interesting is how your characters react.

If you can write emotive, engaging prose, then all the nitty gritty details can be described in a few sentences and your readers will fill in the gaps. If you can connect with them emotionally, sparse technical details will be forgiven. If you can't, then all the physics in the world won't make your novel a winner.

I spent most free time in writing groups, and with writing. Now i await for the response of publisher for the first book. Now i can care about technical details again.

 

[member 656954]

Good luck with it GTOM , let us know when your novel comes out

 

[Steelwolf]

I remember from the old game Traveller that there was the idea of using sand via 'sand casters' to put an ablative shield of refractive sand in the way of lasers, such as the light-reflecting glass spheres they use in road-line paints, signs and for spherical sand-blasting, would diffuse incoming lasers, would confuse heat seeking warheads and missiles, and provide a physical screen against very high velocity projectiles.

Such a 'low tech' defense is one of the better ideas I had seen at the time. Later sci-fi stories point out that even putting a cloud of dust and gas in front of an interstellar magneto-fusion ramjet, and the extreme velocity of the ship meant the gas and dust hit as if it were a solid cloud of gamma and x-rays, and did the corresponding heat damage to the ship, nearly instantly.

Just points to consider.

 

[GTOM]

I remember from the old game Traveller that there was the idea of using sand via 'sand casters' to put an ablative shield of refractive sand in the way of lasers, such as the light-reflecting glass spheres they use in road-line paints, signs and for spherical sand-blasting, would diffuse incoming lasers, would confuse heat seeking warheads and missiles, and provide a physical screen against very high velocity projectiles.

Such a 'low tech' defense is one of the better ideas I had seen at the time. Later sci-fi stories point out that even putting a cloud of dust and gas in front of an interstellar magneto-fusion ramjet, and the extreme velocity of the ship meant the gas and dust hit as if it were a solid cloud of gamma and x-rays, and did the corresponding heat damage to the ship, nearly instantly.

Just points to consider.

Thank you. In my story, closing speed will be 100-200km/s at most.
I think, when they actually use a few frigates as bombs to take out Fort Olympos (deep inside Olympos Mons) the defenders vaporize the ships with nukes, but still much energy reach the mountain, turn much of the surface to obsidian.
Later, the regular missiles finish the job, and collapse the fort.

 

[stefan r]

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 can't 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?

Use tethers. Think of space spiders.

With a basic single cable and two objects you are spiraling toward the target. You can reduce cable length to increase rpm. Increase cable length to spread out and go for low rpm. Instead of 2 objects use dozens (thousands?) and use a full web. With just one cable they might cut the cable. The weights on the cables could be ships (i.e. rocket spiders) capable of independent action or could be a mix of separate disposable systems. If they knock out one fuel tank you still have dozens more. Maybe valuable hardware could be in an armored tank that weighs the same as the fuel tanks.

Use screens rather than shields. You only need a few atoms thickness to block the enemy view. Maybe use bi-layer graphene with a few atoms of metalic coating. You can fold up like an umbrella and make a thick shield if circumstance make that appropriate. A shallow angle is very effective at reflecting laser light. Edge on at 100 km/s a thin film will make a very powerful plasma cutting edge.
Just let a heavy shell/missile pass through the screen. Make sure nothing especially useful is on the other side of that point on the screen. If the enemy explodes into vapor or buckshot you fold up and punch through. The fleet attacks in column formation. The lead ship/web/screen will establish the nature of incoming rounds. The lead ship also punches a hole that the column can pass through.

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.

The explosion would not result in 100% consumption of the anti-matter. Your ship now gets showered with high-energy particles from the explosion. High energy anti-protons and anti-neutrons will impact atomic nuclei inside of your hull and shower your crew with atomic fragments.
If you have anti-matter there is better ways to use it in war. It is very effective fuel so dodging becomes much easier. If you have armories full of anti matter shells that can be used as flak then you only need one little ship to slip into enemy space. You also have to worry about a chain reaction detonating all of the ships in your fleet so you would want to be very spread out.

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...

I would put the fleet in retrograde orbit. That let's you build up momentum during peacetime/coldwar. It would be hard to track stealthy ships if they are not using rocket engines. If they do find your ship/station and sneak attack then some of the debris will still be in retrograde orbit sweeping through their planetary orbit. So they would still have to deal with Kessler syndrome. You might have full asteroids as stations and use mass drivers to eject stealth ships. Meters per second change in orbital speed is enough to move thousands of kilometers in one orbit. Decoys will look a lot like ships while they are drifting.
So one year to come back around. The length of year varies by planet. You might put a few stations out on a Haley's comet like orbit as a reserve and deterrent. For Mercury's battle space the pass frequency is 44 Earth days and the average attack speed is 94 km/s. 97 km/s including orbital speed of Mercury's ships. A ship on an elliptical orbit could do a second pass in less time.

 

[GTOM]

Use tethers. Think of space spiders.

With a basic single cable and two objects you are spiraling toward the target. You can reduce cable length to increase rpm. Increase cable length to spread out and go for low rpm. Instead of 2 objects use dozens (thousands?) and use a full web. With just one cable they might cut the cable. The weights on the cables could be ships (i.e. rocket spiders) capable of independent action or could be a mix of separate disposable systems. If they knock out one fuel tank you still have dozens more. Maybe valuable hardware could be in an armored tank that weighs the same as the fuel tanks.

Use screens rather than shields. You only need a few atoms thickness to block the enemy view. Maybe use bi-layer graphene with a few atoms of metalic coating. You can fold up like an umbrella and make a thick shield if circumstance make that appropriate. A shallow angle is very effective at reflecting laser light. Edge on at 100 km/s a thin film will make a very powerful plasma cutting edge.
Just let a heavy shell/missile pass through the screen. Make sure nothing especially useful is on the other side of that point on the screen. If the enemy explodes into vapor or buckshot you fold up and punch through. The fleet attacks in column formation. The lead ship/web/screen will establish the nature of incoming rounds. The lead ship also punches a hole that the column can pass through. The explosion would not result in 100% consumption of the anti-matter. Your ship now gets showered with high-energy particles from the explosion. High energy anti-protons and anti-neutrons will impact atomic nuclei inside of your hull and shower your crew with atomic fragments.
If you have anti-matter there is better ways to use it in war. It is very effective fuel so dodging becomes much easier. If you have armories full of anti matter shells that can be used as flak then you only need one little ship to slip into enemy space. You also have to worry about a chain reaction detonating all of the ships in your fleet so you would want to be very spread out.
I would put the fleet in retrograde orbit. That let's you build up momentum during peacetime/coldwar. It would be hard to track stealthy ships if they are not using rocket engines. If they do find your ship/station and sneak attack then some of the debris will still be in retrograde orbit sweeping through their planetary orbit. So they would still have to deal with Kessler syndrome. You might have full asteroids as stations and use mass drivers to eject stealth ships. Meters per second change in orbital speed is enough to move thousands of kilometers in one orbit. Decoys will look a lot like ships while they are drifting.
So one year to come back around. The length of year varies by planet. You might put a few stations out on a Haley's comet like orbit as a reserve and deterrent. For Mercury's battle space the pass frequency is 44 Earth days and the average attack speed is 94 km/s. 97 km/s including orbital speed of Mercury's ships. A ship on an elliptical orbit could do a second pass in less time.

Thank you. So you think that defence screen could really work against lots of threats even if it isn't so thick.
At least require pretty much laser power to vaporize it.

So a big missile can shatter into lots of smaller ones protected with a screen, the smaller ones could also use tether propulsion to make their positions less clear. They can ignite second boost phase only when they are close to enemy ship.
(While fighters are still ineffective for deep space attack due to short range, but if one only intends to defend himself, that makes them even more efficient to attack behind the screen, and target thrusters instead of titanium AP warheads.)

Attack fleets can safely evade at least one wave of missiles if they are launched from a distance (planetary defence try to fire at incoming fleet) but a large screen can also boost their survival rate.

I also thought about Mercury colony ensures its safety for a while by sending lots of small probes with nukes into space, alter their course near to the Sun, then they are very hard to track once they chill out.
(Otherwise no one in the story will attack with nukes, and only bomb human settlements as a last desperate effort to stop a rebellion. Most times they try to occupy valuable asteroids, attack cargo ships and bomb only asteroid fortresses.)

 

[essenmein]

The explosion would not result in 100% consumption of the anti-matter. Your ship now gets showered with high-energy particles from the explosion. High energy anti-protons and anti-neutrons will impact atomic nuclei inside of your hull and shower your crew with atomic fragments.
If you have anti-matter there is better ways to use it in war. It is very effective fuel so dodging becomes much easier. If you have armories full of anti matter shells that can be used as flak then you only need one little ship to slip into enemy space. You also have to worry about a chain reaction detonating all of the ships in your fleet so you would want to be very spread out.

I guess the idea of anti matter flak was much more about reducing the incoming mass projectiles into smaller more spread out projectiles so while still damaging, not near as bad as the single larger round it was before.

Anti matter is the primary energy source and the risk of destroying your entire fleet when one ship goes is something people are acutely aware of!

 

[GTOM]

I wondered about the comparison of chemical rocket and fusion reactor.
Lets suppose we have 1kg deuterium. We can burn it with oxygen, or fusion it.
Provided that power output is a few hundred MW at most, how long till all the deuterium is fusioned?
How much trust we could get if we simply burned that amount of deuterium?

 

[essenmein]

I wondered about the comparison of chemical rocket and fusion reactor.
Lets suppose we have 1kg deuterium. We can burn it with oxygen, or fusion it.
Provided that power output is a few hundred MW at most, how long till all the deuterium is fusioned?
How much trust we could get if we simply burned that amount of deuterium?

That ratio of thrust from fusion vs combustion would likely round down to c^2.

 

[GTOM]

That ratio of thrust from fusion vs combustion would likely round down to c^2.

It isn't that simple. Most energy is needed to maintain the fusion reaction. Also i wrote that output is a few MW at most, so it can fusion the hydrogen slowly. Chemical rocket can burn it minutes.