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Long Range Scifi Space Combat


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The Scenario: High thrust constant acceleration is a reality. Could do 1g to mars and back.

Yet electromagnetic pellet cannon shoot faster still.

Pellets like this:

 

https://www.google.com/search?q=shotgun+pellet&client=firefox-b-1-m&source=lnms&tbm=isch&sa=X&ved=0ahUKEwie-9TaoIX2AhV-IUQIHZFKBr0Q_AUIBygC&biw=360&bih=560#imgrc=1iZ1N-FVYkwhCM

 

How fast? Once fired a pellet will coast a light second in only 30 seconds.

Implication: Although scifi likes to show space battles at visual range, the truth is that the more high tech the setting the faster they will be as able shoot ANYTHING beyond visual range.

 

Tactics: I imagine the pellet hitting the hull of a spaceship would hit it like a bomb blast from sheer kinetic energy deposited.

At about a light second or so away, fleets could in theory shoot so as to do area denial... since you do not want to fly where you know relativistic pellets are flying.

 

Real physics: Realistically would it even be possible to shoot pellets of the size depicted at a speed so great it can cross a light second in 30 seconds?

 

I suppose maybe, but the pellets would need to be super cooled to avoid vaporizing from the electromagnetic launch energies (I reckon it may be beyond our current energy  consumption).

 

My guess is the pellets will be supercooled to the point that even their atoms have stopped moving.

Which apparently is not scifi but possible...  https://www.livescience.com/25959-atoms-colder-than-absolute-zero.html

Edited by Spacescifi
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Fundamentally, guided munitions will always have a higher effective range than unguided munitions.

An active sensor pulse to detect "dark" projectiles doesnt depend on the enemy temperature, but is reliant on the resolution of your detector.

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Okay then.

We're talking about a 5g pellet (approximate mass of a 0000 buckshot pellet according to the Wikipedia article attached to your link), travelling at 1x10^7 m/s  (speed of light i.e. 1 light second per second is approximately 3x10^8 m/s, so divide that by 30)

We can ignore relativistic effects at ca. 3% c, so the kinetic energy of that pellet is 5x10^11 J or 500 GJ.

Typical power output for a power station is around 1-2 GW.  

So the kinetic energy of that pellet is equal to around 4-8 minutes of energy production from a large fixed power station.

Hardly beyond our energy consumption but, in the absence of some ultra-high density sci-fi energy source, it does imply that the rate of fire of your hyper railgun is going to be pretty low, simply because it'll require a capacitor bank or equivalent energy storage means which can be charged up over time from a primary generator and then released in a single burst to fire the pellet.

Good for taking out space stations or other fixed targets. Pretty damn useless for ship-to-ship combat, unless you're very confident about your firing solutions.

As for whether the pellet would need to be cooled - that's a complicated question and I have no idea how to figure it out even to a back-of-an-envelope level. One thing that might help though is to use a plasma armature (the armature being the thing that engages with the rails). From Wikipedia:

"The armature may be an integral part of the projectile, but it may also be configured to accelerate a separate, electrically isolated or non-conducting projectile. Solid, metallic sliding conductors are often the preferred form of railgun armature but plasma or 'hybrid' armatures can also be used.[7] A plasma armature is formed by an arc of ionised gas that is used to push a solid, non-conducting payload in a similar manner to the propellant gas pressure in a conventional gun. A hybrid armature uses a pair of plasma contacts to interface a metallic armature to the gun rails. Solid armatures may also 'transition' into hybrid armatures, typically after a particular velocity threshold is exceeded. The high current required to power a railgun can be provided by various power supply technologies, such as capacitors, pulse generators and disc generators."[8]

That would seem to give you more choice of materials to use for your pellet and might allow you to make it out of something suitably insulating, or perhaps to coat it with a protective ablator. This is all just spitballing though.

 

Edit:  Gahhh - brainfart moment.  Forgot to divide by 2 for calculating kinetic energy.  So pellet energy is around 2-4 minutes of output from a large fixed generator. That makes the rate of fire somewhat better - maybe useful against capital ships depending on your setting?

Edited by KSK
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Le sigh. I'm going to regret this.

3 hours ago, Spacescifi said:

Tactics: I imagine the pellet hitting the hull of a spaceship would hit it like a bomb blast from sheer kinetic energy deposited.

A single pellet of 00 buck shot has a mass of 31.5 grams.

At a speed of 30 seconds per light-second, or c/30,  the relativistic kinetic energy of that pellet is 1.57e12 Joules or about 376 tonnes TNT equivalent. That's 34 times the ordnance yield of the largest non-nuclear bomb in the US arsenal, and a little less than the yield of the W54 nuclear warhead, the smallest nuclear warhead ever deployed by the United States.

3 hours ago, Spacescifi said:

Realistically would it even be possible to shoot pellets of the size depicted at a speed so great it can cross a light second in 30 seconds?

Well, you need a gun that can deliver 1.57e12 Joules of energy to the projectile, plus thermal losses. That's going to be rather challenging. An ordinary gun with ordinary propellant can't push a projectile faster than the speed of sound in the gas. A light gas gun can get up to 8.5 km/s but there's a hard limit.

A railgun works up to a few km/s, but railguns require physical contact between the projectile and the rails and so heat becomes an overwhelming problem if you want to go much faster than that. So if you want to go faster, you need an electromagnetic coilgun.

The energy requirements themselves are not THAT overwhelming. If you want to fire one pellet per second, then you need a powerplant which is rated at 1.57e12 Watts. That's only about half the average total power consumption (factoring in gas, electric, etc.) of the entire United States. Surely that will be easy enough to duplicate.

3 hours ago, Spacescifi said:

the pellets would need to be super cooled to avoid vaporizing from the electromagnetic launch energies

Well, for once, your constant concerns about heat and cooling issues have FINALLY proven correct. Because yes, heat is a VERY big problem.

Although it's not the "electromagnetic launch energies" so much as it is the process by which electromagnetic acceleration happens. In a coilgun, you use a magnetic field to induce an opposing magnetic field in a conductive projectile, and the two magnetic fields then interact, which pulls the projectile forward. But induced magnetic fields result in the production of electrical current in the projectile, and electrical current flowing through a metal results in heat (since even very highly conductive materials have SOME resistance). So some percentage of the energy being used by the coilgun is going to be lost to heating the projectile, not as a result of abstract "launch energies" but as a fundamental consequence of the acceleration mechanism.

So there's a fundamental limit to how much velocity your projectile can be given before it melts. Once it melts, the magnetic fields will rip it apart and it won't be able to accelerate further.

15 hours ago, Spacescifi said:

My guess is the pellets will be supercooled to the point that even their atoms have stopped moving.

Well, no -- if you do that, you can't make it interact magnetically.

But supercooling the projectile to begin with won't help much. Even if you start at 0 K, it will still absorb heat energy as a consequence of the acceleration process, so you will still "max out" your speed at the melting point of your metal.

30 minutes ago, KSK said:

We can ignore relativistic effects at ca. 3% c, so the kinetic energy of that pellet is 5x10^11 J or 500 GJ.

You should not ignore relativistic effects at 0.03c; you underestimated kinetic energy by a factor of 3.

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Fortunately for potential targets, zigzagging is a thing. It will be easy enough with torch drive. And made even more effective by 3d environment.

TL;DR: Enemy commander needs to order small course change in a random direction every couple of minutes.

Considering the size of space, amount of pellets that would be needed would be prohibitively large.

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The opponent launches a bubble, the pellet hits it, and gets either evaporated or deflected.

Btw. If a surface tension of the bubble fluid is enough high to keep the fluid vapour pressure, it can be a soap bubble cannon for relativistic space combat.

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Anyone who wants to think/theorize/fantasize about space combat at relativistic speeds I would recommend to read "Protector" by Larry Niven. Without going into the plot, there is a chapter or 2 where the protagonists are basically in a race to reach a destination first while being chased by aliens, and along the way they take a lot of potshots at each other using missiles and lasers. I'm not going to say it's all scientifically accurate (for one, it's been quite a while since I last read it) but he definitely put some thought in all the strange effects you have to deal with when trying to hit an enemy ship while both traveling at a significant fraction of light speed (and how to avoid being hit). It was quite an exhilarating read as I recall.

In this particular story they use Bussard Ramjets to reach these speeds which means that they will typically be under acceleration, at which point using any sort of 'cannon' is really quite pointless. All you have to do is put some matter at the right place and time. If the enemy ship runs into it it's game over. He also put some work into the whole question of how you detect (or don't detect) an incoming projectile when everything is blue-shifted into X-ray territory.

 

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2 hours ago, sevenperforce said:

A single pellet of 00 buck shot has a mass of 31.5 grams.

from http://blog.beretta.com/everything-you-need-to-know-about-shotgunning-with-buckshot

Quote

The #00 Buck pellet weighs 53.8 grains. 

Which is 3,5 grams. Still a big boom, but changes the rate of fire quite a bit.

17 hours ago, Spacescifi said:

My guess is the pellets will be supercooled to the point that even their atoms have stopped moving.

Which apparently is not scifi but possible...  https://www.livescience.com/25959-atoms-colder-than-absolute-zero.html

Yeah, that is being misrepresented almost as badly as the sum of all positive integers being -1/12.

Negative temperatures are not a thing.

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2 hours ago, sevenperforce said:

Le sigh. I'm going to regret this.

A single pellet of 00 buck shot has a mass of 31.5 grams.

At a speed of 30 seconds per light-second, or c/30,  the relativistic kinetic energy of that pellet is 1.57e12 Joules or about 376 tonnes TNT equivalent. That's 34 times the ordnance yield of the largest non-nuclear bomb in the US arsenal, and a little less than the yield of the W54 nuclear warhead, the smallest nuclear warhead ever deployed by the United States.

Well, you need a gun that can deliver 1.57e12 Joules of energy to the projectile, plus thermal losses. That's going to be rather challenging. An ordinary gun with ordinary propellant can't push a projectile faster than the speed of sound in the gas. A light gas gun can get up to 8.5 km/s but there's a hard limit.

A railgun works up to a few km/s, but railguns require physical contact between the projectile and the rails and so heat becomes an overwhelming problem if you want to go much faster than that. So if you want to go faster, you need an electromagnetic coilgun.

Well 376 ton TNT, I say its a bit overkill unless you are up against something very large an well armored like an fortified asteroid base or an mega structure, first I would make the shell larger say one kilogram, and energy less than an ton TNT, even that is overkill against something like an battleship, remember an larger heavy metal shell will carry much more momentum so it will penetrate more armor rather than turn into radiation hitting an soap bubble. 
Don't think that will work so well but could easy see solar sail style structures being used as disposable wipple shield. 
Again unless you fight something like an battleship I would go down in projectile energy and size. Yes downside going slower is that its easier to dodge. 

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7 hours ago, KSK said:

Okay then.

We're talking about a 5g pellet (approximate mass of a 0000 buckshot pellet according to the Wikipedia article attached to your link), travelling at 1x10^7 m/s  (speed of light i.e. 1 light second per second is approximately 3x10^8 m/s, so divide that by 30)

We can ignore relativistic effects at ca. 3% c, so the kinetic energy of that pellet is 5x10^11 J or 500 GJ.

Typical power output for a power station is around 1-2 GW.  

So the kinetic energy of that pellet is equal to around 4-8 minutes of energy production from a large fixed power station.

Hardly beyond our energy consumption but, in the absence of some ultra-high density sci-fi energy source, it does imply that the rate of fire of your hyper railgun is going to be pretty low, simply because it'll require a capacitor bank or equivalent energy storage means which can be charged up over time from a primary generator and then released in a single burst to fire the pellet.

Good for taking out space stations or other fixed targets. Pretty damn useless for ship-to-ship combat, unless you're very confident about your firing solutions.

As for whether the pellet would need to be cooled - that's a complicated question and I have no idea how to figure it out even to a back-of-an-envelope level. One thing that might help though is to use a plasma armature (the armature being the thing that engages with the rails). From Wikipedia:

"The armature may be an integral part of the projectile, but it may also be configured to accelerate a separate, electrically isolated or non-conducting projectile. Solid, metallic sliding conductors are often the preferred form of railgun armature but plasma or 'hybrid' armatures can also be used.[7] A plasma armature is formed by an arc of ionised gas that is used to push a solid, non-conducting payload in a similar manner to the propellant gas pressure in a conventional gun. A hybrid armature uses a pair of plasma contacts to interface a metallic armature to the gun rails. Solid armatures may also 'transition' into hybrid armatures, typically after a particular velocity threshold is exceeded. The high current required to power a railgun can be provided by various power supply technologies, such as capacitors, pulse generators and disc generators."[8]

That would seem to give you more choice of materials to use for your pellet and might allow you to make it out of something suitably insulating, or perhaps to coat it with a protective ablator. This is all just spitballing though.

 

Edit:  Gahhh - brainfart moment.  Forgot to divide by 2 for calculating kinetic energy.  So pellet energy is around 2-4 minutes of output from a large fixed generator. That makes the rate of fire somewhat better - maybe useful against capital ships depending on your setting?

 

Plasma armature? That's interesting... yet once again as per the usual the limit would be the melting point of the pellet.

Plasma railgun anyone? Only problem there is that plasma projectiles are apparently even more wispy than gas... lots if damage it won't do at distant range due to plasma scattering and not staying focused.

6 hours ago, Scotius said:

Fortunately for potential targets, zigzagging is a thing. It will be easy enough with torch drive. And made even more effective by 3d environment.

TL;DR: Enemy commander needs to order small course change in a random direction every couple of minutes.

Considering the size of space, amount of pellets that would be needed would be prohibitively large.

Yes and no.

Yes: Requires the RCS to use a similar but smaller engine based on the main engine. A mini-torch drive RCS for efficiency is what you really need to dodge maneuver offten.

No: Even if we had torchdrives we may not want them for RCS as the exhaust could radiate or burn stuff during docking or landing in space or elsewhere.

Assuming you use good old fashioned gas or chemical RCS, then you can only afford so many maneuvers before you can no longer manever anyway but straight from main engined.

7 hours ago, sevenperforce said:

Le sigh. I'm going to regret this.

A single pellet of 00 buck shot has a mass of 31.5 grams.

At a speed of 30 seconds per light-second, or c/30,  the relativistic kinetic energy of that pellet is 1.57e12 Joules or about 376 tonnes TNT equivalent. That's 34 times the ordnance yield of the largest non-nuclear bomb in the US arsenal, and a little less than the yield of the W54 nuclear warhead, the smallest nuclear warhead ever deployed by the United States.

Well, you need a gun that can deliver 1.57e12 Joules of energy to the projectile, plus thermal losses. That's going to be rather challenging. An ordinary gun with ordinary propellant can't push a projectile faster than the speed of sound in the gas. A light gas gun can get up to 8.5 km/s but there's a hard limit.

A railgun works up to a few km/s, but railguns require physical contact between the projectile and the rails and so heat becomes an overwhelming problem if you want to go much faster than that. So if you want to go faster, you need an electromagnetic coilgun.

The energy requirements themselves are not THAT overwhelming. If you want to fire one pellet per second, then you need a powerplant which is rated at 1.57e12 Watts. That's only about half the average total power consumption (factoring in gas, electric, etc.) of the entire United States. Surely that will be easy enough to duplicate.

Well, for once, your constant concerns about heat and cooling issues have FINALLY proven correct. Because yes, heat is a VERY big problem.

Although it's not the "electromagnetic launch energies" so much as it is the process by which electromagnetic acceleration happens. In a coilgun, you use a magnetic field to induce an opposing magnetic field in a conductive projectile, and the two magnetic fields then interact, which pulls the projectile forward. But induced magnetic fields result in the production of electrical current in the projectile, and electrical current flowing through a metal results in heat (since even very highly conductive materials have SOME resistance). So some percentage of the energy being used by the coilgun is going to be lost to heating the projectile, not as a result of abstract "launch energies" but as a fundamental consequence of the acceleration mechanism.

So there's a fundamental limit to how much velocity your projectile can be given before it melts. Once it melts, the magnetic fields will rip it apart and it won't be able to accelerate further.

Well, no -- if you do that, you can't make it interact magnetically.

But supercooling the projectile to begin with won't help much. Even if you start at 0 K, it will still absorb heat energy as a consequence of the acceleration process, so you will still "max out" your speed at the melting point of your metal.

You should not ignore relativistic effects at 0.03c; you underestimated kinetic energy by a factor of 3.

 

Interesting post!

I was unaware if atoms stopped moving that the pellet would be magnetically neutral.... makes sense though because electrons need to flow to do much.

I had assumed getting objects colder and colder could be done to infinity, since one can virtually do so with heating objects.

I say virtually because their may be a limit but I am unaware.... after all even stars have their limits.

It would seem the solution to a melting pellet would be one of two choices:

 

1. Use a real material like tungsten for the pellets and forget the lightsecond every 30 seconds speed.

 

2. Use a handwavium fictional metal that has a higher than normal melting point. Of course such would be used for vessel hull.... making lasers reduced in effectiveness.

Interesting

9 hours ago, Rakaydos said:

Fundamentally, guided munitions will always have a higher effective range than unguided munitions.

An active sensor pulse to detect "dark" projectiles doesnt depend on the enemy temperature, but is reliant on the resolution of your detector.

 

Well yes and no.

 

If a spaceship is only 300 kilometers away and I fire the lightsecond in 30 seconds pellet it is likely going to get hit with it.

 

Weapons this fast force all combat into long range.

And also means that anywhere from 300 to a thousand kilomters is a nigh guaranteed kill zone... likely farther than that.... but feel free to calculate the effective range of the relativistic pellet gun.

Edited by Spacescifi
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9 hours ago, Shpaget said:
11 hours ago, sevenperforce said:

A single pellet of 00 buck shot has a mass of 31.5 grams.

from http://blog.beretta.com/everything-you-need-to-know-about-shotgunning-with-buckshot

Quote

The #00 Buck pellet weighs 53.8 grains. 

Which is 3,5 grams. Still a big boom, but changes the rate of fire quite a bit.

Ooooh I see now. I was accidentally using the total load weight of 1.11 ounces (484 grains or 32.5 grams) rather than the weight of the individual pellets. There are 9 pellets of 00 buckshot in a standard load, so I’m off by a factor of 9. Fortunately, the equation for relativistic kinetic energy is linear with respect to rest mass, so I just have to divide all my numbers by 9.

So if you want to fire one pellet per second, you don’t need half the total power consumption of the United States; you only need 4.5% of the total power consumption of the United States, or approximately the same as the total continuous power consumption of the state of New York. Totally doable.

And the relativistic kinetic energy of the explosion on impact will be only 4 times the blast yield of the largest non-nuclear bomb in the US arsenal.

8 hours ago, magnemoe said:

Again unless you fight something like an battleship I would go down in projectile energy and size. Yes downside going slower is that its easier to dodge. 

Yes, but the accelerations required to dodge a projectile moving above solar escape velocity (which itself is a tiny fraction of low relativistic velocities) are so wildly high that dodging is simply not an option.

4 hours ago, Spacescifi said:

Plasma armature? That's interesting... yet once again as per the usual the limit would be the melting point of the pellet.

So actually this is NOT a problem with a plasma armature rail gun. A plasma armature can accelerate at arbitrarily high speeds and can push a non-conductive projectile at the same speeds. The accelerations are high enough that you don’t have enough time for the projectile to heat up.

I should look into this.

4 hours ago, Spacescifi said:

I had assumed getting objects colder and colder could be done to infinity, since one can virtually do so with heating objects.

Nope. Categorically nope. Haven’t you ever heard of absolute zero?

4 hours ago, Spacescifi said:

Use a real material like tungsten for the pellets and forget the lightsecond every 30 seconds speed.

Yes, that is your solution. The speeds you’re proposing are completely overkill. 

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You know - the more I read @Spacescifi's posts, and think of shows like Expanse (where both are *mostly* trying to do 'hard scifi' or at least not bend the current understanding of physics too much)...  I'm reminded that we started riding horses 5500 years ago, and that only changed a bit over 100 years ago.

Until & unless we make some kind of revolutionary leap in understanding, we are stuck in our own neighborhood for a loooong time.

That said - this has been an interesting read; thank everyone!

Edited by JoeSchmuckatelli
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10 hours ago, Spacescifi said:

I had assumed getting objects colder and colder could be done to infinity, since one can virtually do so with heating objects.

Nope. 

  • From Heisenberg's Uncertainty Principle, there are pairs of variables for which you cannot simultaneously know them both exactly. 
  • Momentum and position are one such pair, so if you know the exact position of a particle you cannot know its exact momentum and vice versa.
  • If you were able to cool a particle to absolute zero, so that it stops moving, you would be able to know its exact position and momentum (zero) - which is forbidden by the Uncertainty Principle.
  • Therefore all particles have some momentum, thus kinetic energy, thus temperature.

It's been ages since I did any of this, so this is probably a very clunky way of putting it.

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10 hours ago, sevenperforce said:

Ooooh I see now. I was accidentally using the total load weight of 1.11 ounces (484 grains or 32.5 grams) rather than the weight of the individual pellets. There are 9 pellets of 00 buckshot in a standard load, so I’m off by a factor of 9. Fortunately, the equation for relativistic kinetic energy is linear with respect to rest mass, so I just have to divide all my numbers by 9.

So if you want to fire one pellet per second, you don’t need half the total power consumption of the United States; you only need 4.5% of the total power consumption of the United States, or approximately the same as the total continuous power consumption of the state of New York. Totally doable.

And the relativistic kinetic energy of the explosion on impact will be only 4 times the blast yield of the largest non-nuclear bomb in the US arsenal.

Yes, but the accelerations required to dodge a projectile moving above solar escape velocity (which itself is a tiny fraction of low relativistic velocities) are so wildly high that dodging is simply not an option.

So actually this is NOT a problem with a plasma armature rail gun. A plasma armature can accelerate at arbitrarily high speeds and can push a non-conductive projectile at the same speeds. The accelerations are high enough that you don’t have enough time for the projectile to heat up.

I should look into this.

Nope. Categorically nope. Haven’t you ever heard of absolute zero?

Yes, that is your solution. The speeds you’re proposing are completely overkill. 

 

Nice! Thanks!

Amusingly enough tungsten pellets will work just fine... since if they only spend a nanosecond on the plasma armature during launch or less they totally can survive it.

I still remember my old post of what would happen if a person teleported to the sun for a millisecond and teleported back to Earth.

The answers were both scientific and humorous but they revealed that a millisecond is certain death.... but a nanosecond is actually survivable.

I really can keep the OP railgun speeds and still use tungsten pellets!

Interestingly plasma armature railguns could ALSO be used for space travel.

At lower velocities of course, but once you seed a bunch of these around the solar system you could chuck stuff all over and use each railgun to slow or speed up ships or probes that passed through their plasma armatures. All with minimal propellant use.

 

The main potential issue is ensuring vessels pass safely through the plasma armature instead of utterly ramming the railgun and obliterating them both.

Other uses: Do you have a moon base? It's no longer safe. Do you have an orbital space station? Ditto.

Any non-maneuvering target is toast or swiss cheese.... literally being shot up with holes.

Orbital bombardment? Doubt it. The pellet would explode in the upper atmosphere at the speed it is flying. That said it would be an effective weapon to prevent land based ICBM's from launching.... maybe?

Since firing off a few rounds may cause an explosion big enough to wreck an ICBM or screw up it's trajectory or guidance systems... even without a direct hit.

6 hours ago, JoeSchmuckatelli said:

You know - the more I read @Spacescifi's posts, and think of shows like Expanse (where both are *mostly* trying to do 'hard scifi' or at least not bend the current understanding of physics too much)...  I'm reminded that we started riding horses 5500 years ago, and that only changed a bit over 100 years ago.

Until & unless we make some kind of revolutionary leap in understanding, we are stuck in our own neighborhood for a loooong time.

That said - this has been an interesting read; thank everyone!

 

I am rather certain (98.99%) that my OP railgun using the plasma armature railgun KSK mentioned would be more overpowered than even the weapons in The Expanse.

Missiles become short range weapons when they can be sniped by relativistic pellets fired every second.

A spaceship with my OP weapon is like death incarnate at long range.

The only way you are killing it is if you also have a similar weapon. Otherwise you may as well stay home. It would be like bringing a knife to a gunfight.... or a bow and arrow to a machine gun fight.

Edited by Spacescifi
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15 hours ago, Spacescifi said:

 

 

Well yes and no.

 

If a spaceship is only 300 kilometers away and I fire the lightsecond in 30 seconds pellet it is likely going to get hit with it.

 

Weapons this fast force all combat into long range.

And also means that anywhere from 300 to a thousand kilomters is a nigh guaranteed kill zone... likely farther than that.... but feel free to calculate the effective range of the relativistic pellet gun.

All weapons that fast do is redefine "long range." Past the point where a torch drive CAN dodge your nearlight pellet, a missile (or dronefighter) will be able to follow the enemy maneuvers, enter the killzone, and make it's own attack.

Notably, as point defense gets batter, missiles need more standoff range. If ship-style weapons are more effective, then the missile becomes a disposable fighterdrone, with it's own ship style weapon with the same killzone as ship weapons, but still fundamentally a missile, trading mission endurance for evasion and power, fired in the hopes of damaging the enemy before it's destroyed or runs out of power.

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34 minutes ago, Rakaydos said:

All weapons that fast do is redefine "long range." Past the point where a torch drive CAN dodge your nearlight pellet, a missile (or dronefighter) will be able to follow the enemy maneuvers, enter the killzone, and make it's own attack.

Notably, as point defense gets batter, missiles need more standoff range. If ship-style weapons are more effective, then the missile becomes a disposable fighterdrone, with it's own ship style weapon with the same killzone as ship weapons, but still fundamentally a missile, trading mission endurance for evasion and power, fired in the hopes of damaging the enemy before it's destroyed or runs out of power.

 

You saw the power requirements of the railgun from sevenperforce?

If fired once every second that is energy comsumption of New Jersey!

A small missile is unlikely to be packing such a powerplant, especially since it is disposable.

Unless there are more missiles than can reasonably be shot down the battleship with the pellet gun wins. Utterly.

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On 2/17/2022 at 5:23 AM, KSK said:

Okay then.

We're talking about a 5g pellet (approximate mass of a 0000 buckshot pellet according to the Wikipedia article attached to your link), travelling at 1x10^7 m/s  (speed of light i.e. 1 light second per second is approximately 3x10^8 m/s, so divide that by 30)

We can ignore relativistic effects at ca. 3% c, so the kinetic energy of that pellet is 5x10^11 J or 500 GJ.

Typical power output for a power station is around 1-2 GW.  

So the kinetic energy of that pellet is equal to around 4-8 minutes of energy production from a large fixed power station.

Hardly beyond our energy consumption but, in the absence of some ultra-high density sci-fi energy source, it does imply that the rate of fire of your hyper railgun is going to be pretty low, simply because it'll require a capacitor bank or equivalent energy storage means which can be charged up over time from a primary generator and then released in a single burst to fire the pellet.

Good for taking out space stations or other fixed targets. Pretty damn useless for ship-to-ship combat, unless you're very confident about your firing solutions.

As for whether the pellet would need to be cooled - that's a complicated question and I have no idea how to figure it out even to a back-of-an-envelope level. One thing that might help though is to use a plasma armature (the armature being the thing that engages with the rails). From Wikipedia:

"The armature may be an integral part of the projectile, but it may also be configured to accelerate a separate, electrically isolated or non-conducting projectile. Solid, metallic sliding conductors are often the preferred form of railgun armature but plasma or 'hybrid' armatures can also be used.[7] A plasma armature is formed by an arc of ionised gas that is used to push a solid, non-conducting payload in a similar manner to the propellant gas pressure in a conventional gun. A hybrid armature uses a pair of plasma contacts to interface a metallic armature to the gun rails. Solid armatures may also 'transition' into hybrid armatures, typically after a particular velocity threshold is exceeded. The high current required to power a railgun can be provided by various power supply technologies, such as capacitors, pulse generators and disc generators."[8]

That would seem to give you more choice of materials to use for your pellet and might allow you to make it out of something suitably insulating, or perhaps to coat it with a protective ablator. This is all just spitballing though.

 

Edit:  Gahhh - brainfart moment.  Forgot to divide by 2 for calculating kinetic energy.  So pellet energy is around 2-4 minutes of output from a large fixed generator. That makes the rate of fire somewhat better - maybe useful against capital ships depending on your setting?

 

Apparently plasma armatures are not without issues and that limits their firing speed.

https://ieeexplore.ieee.org/document/22574

Yet the issuee seem like 'engineering problems' more than 'defy the laws of physics problems'.

So it is not a show stopper for scifi.

Edited by Spacescifi
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Eve

1 hour ago, Spacescifi said:

Amusingly enough tungsten pellets will work just fine... since if they only spend a nanosecond on the plasma armature during launch or less they totally can survive it.

Have you tried calculating the power requirements for this?

Also, do not neglect Newton's third law. Firing a kinetic weapon that has energy equivalent of an almost-a-nuke, will produce a recoil of equivalent energy.

Edited by Shpaget
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1 hour ago, Spacescifi said:

 

You saw the power requirements of the railgun from sevenperforce?

If fired once every second that is energy comsumption of New Jersey!

A small missile is unlikely to be packing such a powerplant, especially since it is disposable.

Unless there are more missiles than can reasonably be shot down the battleship with the pellet gun wins. Utterly.

A missile doesnt have to power it continuously. All it needs is a few good shots, inside the killzone of the weapon.

Notably, since a missile can be designed to handle higher gs than a crewed ship, and is physically smaller, the range at which a ship can reliably hit an evading missile is SMALLER than the range a missile can reliably hit an evading ship. 

That gives the missiles an advantage in engagement envelope.

Edited by Rakaydos
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19 minutes ago, Shpaget said:

Eve

Have you tried calculating the power requirements for this?

Also, do not neglect Newton's third law. Firing a kinetic weapon that has energy equivalent of an almost-a-nuke, will produce a recoil of equivalent energy.

 

Thanks.... so a massive battleship is needed to 'cushion' the recoil.

Unlike Star Trek yet ironically so, every time the Captain gives the order to fire the relativistic railgun the crew would lurch forward at 1g from the recoil lol.

21 minutes ago, Rakaydos said:

A missile doesnt have to power it continuously. All it needs is a few good shots, inside the killzone of the weapon.

Notably, since a missile can be designed to handle higher gs than a crewed ship, and is physically smaller, the range at which a ship can reliably hit an evading missile is SMALLER than the range a missile can reliably hit an evading ship. 

That gives the missiles an advantage in engagement envelope.

Won't matter if the battleship has multiple railgun turrets all firing at the same target.

And a missile with a powerplant of it's own is a one-shot and done kind... unless it's a small ship itself

25 minutes ago, Shpaget said:

Eve

Have you tried calculating the power requirements for this?

Also, do not neglect Newton's third law. Firing a kinetic weapon that has energy equivalent of an almost-a-nuke, will produce a recoil of equivalent energy.

 

Nope... but if a human can survive the surface of the sun of teleported there and back for a nanosecond... the tungsten pellet should be alright.

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5 minutes ago, Spacescifi said:

 

Nope... but if a human can survive the surface of the sun of teleported there and back for a nanosecond... the tungsten pellet should be alright.

Those two examples are fundamentally different. Spending shorter amount of time on the surface of the Sun transfers smaller amount of energy into the human, while spending shorter amount of time to accelerate to a given speed imparts the same energy into the pellet as if it was accelerating for a longer period.

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3 minutes ago, Shpaget said:

Those two examples are fundamentally different. Spending shorter amount of time on the surface of the Sun transfers smaller amount of energy into the human, while spending shorter amount of time to accelerate to a given speed imparts the same energy into the pellet as if it was accelerating for a longer period.

Just reduce the time even more then.... oh I get it... the tungsten is vaporized no matter what.

 

Oh well... I tried and physics won in the end.

Turns out that physics does not make it easy for humans to make uber space weapons.... perhaps that is for the best.

I would have to use unobtanium pellets (fictional metal with a ridiculously high melting point) that is likely used for hull armor too.

Duralium, duranium... same thing I guess.

Bonus is that now lasers really are kind of nigh obsolete.

So railguns would truly be the most viable weapon in such a setting unless one had thousands of missiles to waste.

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14 minutes ago, Spacescifi said:

Thanks.... so a massive battleship is needed to 'cushion' the recoil.

For the love of Heinlein, just take a minute or two to do a rough calculation.

5g pellet moving at 1x10^7 m/s has a momentum of 5x10^4 kg m/s.

So for a recoil velocity of 1 m/s you need a ship mass of 5x10^4 kg or 50 metric tonnes.

That’s not even a particularly massive spacecraft by present day standards.

That’s neglecting relativistic effects so, which, as pointed out by @sevenperforce  is incorrect, so this is not an accurate calculation but it does at least give you some idea of scale.

Frankly, given the mass of ship that you’d need to fit this railgun to and the mass of powerplant needed to fire it, recoil is pretty much negligible. 

 

8 minutes ago, Spacescifi said:

Oh well... I tried and physics won in the end.

Well you also ignored the main advantage (as suggested by myself and then pointed out again by @sevenperforce) of using a plasma armature - which is that your projectile can be made of a non-conductive material, thus getting around the whole vaporising pellet problem.

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