High energy laser vs supervelocity missile

[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.