Long Range Scifi Space Combat

[Rakaydos]

39 minutes ago, Spacescifi said:

 

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

Wont matter if multiple missiles are firing in a volley at the ship.

Anything the ship can so, the missile volley can do better... once.

[Spacescifi]

26 minutes ago, KSK said:

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. 

 

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.

Wait... you are saying the energy will be less if a non-conductive mass is used?

Even then it must be heat resistant since the plasma I reckon will be hot... unless we use 'cold plasma'... would low heat or cold plasmas even allow for such a feat?

So overall you are saying that the OP could work in theory... but the unanswered question is just how much heat transfer the pellet will have to survive.

Since even if does not conduct electricity it will still conduct heat as all mass does that.

21 minutes ago, Rakaydos said:

Wont matter if multiple missiles are firing in a volley at the ship.

Anything the ship can so, the missile volley can do better... once.

 

Depends on both acceleration and range.

If you start with 50 missiles in mars low orbit and a battleship with the pellet plasma armature railgun in Earth low orbit, and the missiles max out at 20g continous, but the battleship maxes out at 3g then the missiles will be be at a disadvantage.

 

Why? Because the battleship has the sniping pellet railgun turrets AND 20g continous acceleration missiles of it's own.

And shipbased anti-missiles could carry all sorts of anti-missile packages that do not require them to even directly collide with the missiles.

Shrapnel, machine guns, nuke ECM.... sure there are more still.

[Rakaydos]

42 minutes ago, Spacescifi said:

 

 

Depends on both acceleration and range.

If you start with 50 missiles in mars low orbit and a battleship with the pellet plasma armature railgun in Earth low orbit, and the missiles max out at 20g continous, but the battleship maxes out at 3g then the missiles will be be at a disadvantage.

 

Why? Because the battleship has the sniping pellet railgun turrets AND 20g continous acceleration missiles of it's own.

And shipbased anti-missiles could carry all sorts of anti-missile packages that do not require them to even directly collide with the missiles.

Shrapnel, machine guns, nuke ECM.... sure there are more still.

...and now we're evolving into space-fighter dogfighting.  Missiles shooting at other missiles to keep them from shooting at the motherships. But in a passing engagement at nearlight velocities.

Which is rather my point. There's a reason modern navies dont field Battleships anymore, it's all about Carriers, and support ships to protect the carriers (Though, instead of taking advantage if the difference between water transportation and air transportation, it's taking advantage of not having to keep humans un-pancaked)

[KSK]

58 minutes ago, Spacescifi said:

Wait... you are saying the energy will be less if a non-conductive mass is used?

Even then it must be heat resistant since the plasma I reckon will be hot... unless we use 'cold plasma'... would low heat or cold plasmas even allow for such a feat?

So overall you are saying that the OP could work in theory... but the unanswered question is just how much heat transfer the pellet will have to survive.

Quoting directly from @sevenperforce’s post. 

“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.”

So, in a nutshell, yes, the OP could work in theory using a plasma armature.

 

[sevenperforce]

7 hours ago, KSK said:

Quoting directly from @sevenperforce’s post. 

“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.”

So, in a nutshell, yes, the OP could work in theory using a plasma armature.

In practice, a deployable plasma armature railgun projectile would look a lot like a conventional firearm cartridge. The projectile itself would likely be a depleted uranium slug with a ceramic jacket, not unlike the rounds fired from the GAU Avenger on the A-10 Warthog (although those have a metal jacket on the DU core). Behind the projectile, you’d have the material designed to vaporize and form into the plasma armature…some sort of metal, possibly with an initiator explosive in it to trigger the vaporization.

To answer @Spacescifi’s question: no, a “cold plasma” absolutely won’t work.

What you are basically doing, in a plasma armature railgun, is creating a ball of artificial lightning and accelerating that ball of lightning at ludicrous speeds, using it to push your non-conductive projectile. The challenge is figuring out how to keep the electricity flow from going anywhere other than through the plasma armature. You’d probably need to pull a vacuum in the barrel and then backfill the barrel with a nonconductive gas as the round is fired.

Most of the limitations here are going to center around the engineering of the plasma armature. The only hard physics limit here is going to be dictated by the length of your gun barrel, the diameter of your bore, and the compressive strength of your projectile. Since your ball of lightning is pushing the projectile from behind, not unlike in a conventional firearm, there is a limit to how much acceleration you can subject your projectile to before it crumbles. The compressive strength of tungsten is 142,000 psi, so depending on the size of the bore, you can calculate the maximum gees you can pull without cracking the tungsten; with max gees you can calculate how long of a barrel you need to hit any desired velocity. 

[Spacescifi]

16 hours ago, sevenperforce said:

In practice, a deployable plasma armature railgun projectile would look a lot like a conventional firearm cartridge. The projectile itself would likely be a depleted uranium slug with a ceramic jacket, not unlike the rounds fired from the GAU Avenger on the A-10 Warthog (although those have a metal jacket on the DU core). Behind the projectile, you’d have the material designed to vaporize and form into the plasma armature…some sort of metal, possibly with an initiator explosive in it to trigger the vaporization.

To answer @Spacescifi’s question: no, a “cold plasma” absolutely won’t work.

What you are basically doing, in a plasma armature railgun, is creating a ball of artificial lightning and accelerating that ball of lightning at ludicrous speeds, using it to push your non-conductive projectile. The challenge is figuring out how to keep the electricity flow from going anywhere other than through the plasma armature. You’d probably need to pull a vacuum in the barrel and then backfill the barrel with a nonconductive gas as the round is fired.

Most of the limitations here are going to center around the engineering of the plasma armature. The only hard physics limit here is going to be dictated by the length of your gun barrel, the diameter of your bore, and the compressive strength of your projectile. Since your ball of lightning is pushing the projectile from behind, not unlike in a conventional firearm, there is a limit to how much acceleration you can subject your projectile to before it crumbles. The compressive strength of tungsten is 142,000 psi, so depending on the size of the bore, you can calculate the maximum gees you can pull without cracking the tungsten; with max gees you can calculate how long of a barrel you need to hit any desired velocity. 

 

Hmmm... reality strikes again.

 

Why am I thinking the battleship would end up having a kilometer or several kilometers long railgun to achieve the required 30 seconds per lighsecond speed?

You would literally build the spaceship around the railgun, or simply attach it when in use and detach it when not in use.... leaving it to orbit somewhere in safe keeping with a fleet or station. Portable railgun... interchangeable between ships.

 

I guess this kills the multiple turret railgun idea for scifi I was thinking of... at least if I was going for maximum realism.... which I am not.

The scifi way to achieve multiple OP turret railguns would be to just use unobtanium materials with ridicously high melting points.

Yet it is still interesting to note how you would not be fooling anyone about what kind of spaceship you have if a several kilometers long spinally mounted railgun is mounted on it's nose.... which seems to he what reality dictates for the OP.

Small turrets cannot realistically do the OP withouut scifi make believe.

Well.. there is one way but it would involve pusher plates and nukes.... which would quickly be more expensive than the pellets being shot off by them.

 

That is an interesting idea though, using a shaped charge nuke to propel a bunch of shotgun pellets in space.

 

Edited February 19, 2022 by Spacescifi

[KSK]

Hmmm, actually you might want to think in terms of Death Stars.

Let's see if I've got this right. 

142,000 psi = 980,000 KPa or 9.8 x10⁸ Nm^-2. 

Lets go with a 5g pellet again. Density of tungsten is 19.25g per cubic centimetre, so we need a volume of 0.26 cubic centimetres or 2.6x10-7 cubic metres.

Lets assume a spherical pellet for simplicity.  We need a radius of approximately 0.004 m

Surface area of that pellet is 6.4x10-5 m2, so surface area of half the pellet is (very roughly) 3.2 x 10^-5 m².

OK, this is where things get seriously approximated.  1, I'm going to ignore relativistic effects, 2, I'm going to assume that the pellet is incompressible, 3. I'm going to assume that the force from the armature is applied evenly across its surface. In practice, I don't expect any of those assumptions to be valid but they make the calculation a lot more tractable and I'm only doing this to get an idea of scale anyway.

Maximum force on the pellet is 9.8x10⁸ Nm^-2 x 3.2x10^-5 m² = 31,000 N, rounding down.

Therefore maximum acceleration the pellet undergoes is 6.2 x 10⁶ ms^-2.

So to reach 1x10⁷ m/s requires 1.6s

Distance the pellet travels in that time = 1/2at² or approximately 5,000 km.

 

That's quite the railgun.  Not that great for point defense, I'm thinking.

If anyone else is inclined to do the calculation, I'd welcome the sanity check. I did check but I may well have stuffed up a unit conversion somewhere along the line, or the whole thing could simply be duff.

If not though - I really don't care what the 5,000 km warship is packing - I'm leaving for the next star system over.

 

Edited February 19, 2022 by KSK

[sevenperforce]

On 2/19/2022 at 1:19 PM, KSK said:

Distance the pellet travels in that time = 1/2at² or approximately 5,000 km.

 

That's quite the railgun.  Not that great for point defense, I'm thinking.

If anyone else is inclined to do the calculation, I'd welcome the sanity check. I did check but I may well have stuffed up a unit conversion somewhere along the line, or the whole thing could simply be duff.

If not though - I really don't care what the 5,000 km warship is packing - I'm leaving for the next star system over.

My Fermi Estimation (which I did before posting the compressive strength of tungsten) gave a barrel length of 800 km, so you pass sanity check. That’s why I posted the compressive strength; I was busy and didn’t want to do all the math to come up with the real number. 

[Spacescifi]

5 hours ago, sevenperforce said:

My Fermi Estimation (which I did before posting the compressive strength of tungsten) gave a barrel length of 800 km, so you pass sanity check. That’s why I posted the compressive strength; I was busy and didn’t want to do all the math to come up with the real number. 

 

Hmmm... is there a way to artficially increase the diamagnetic properties of a material?

If so that could allow for multiple smaller railgun turrets with the OP velocity.

 

I know the velocity is a bit of stretch, but nonetheless the fact that electromagnets can be toggled on and off means a hyper-diamagnetic slug could be launched without heating it at all in space.

In fact, the more diamagnetic it is the less powerful railgun you would need to propel it to the OP speed.

 

About Diamagnetism:

Diamagnetism

A diamagnetic substance is one whose atoms have no permanent magnetic dipole moment. When an external magnetic field is applied to a diamagnetic substance such as bismuth or silver a weak magnetic dipole moment is induced in the direction opposite the applied field. All materials are actually diamagnetic, in that a weak repulsive force is generated by in a magnetic field by the current of the orbiting electron. Some materials, however, have stronger paramagnetic qualities that overcome their natural diamagnetic qualities. These paramagnetic materials, such as iron and nickel, have unpaired electrons.

Some Diamagnetic Elements

Bismuth

Mercury

Silver

Carbon

Lead

Copper

 

How a civilization could go about increasing the diamagnetism of an element or compound is beyond me, but I am aware that the ability to do that would open up or imply plenty of others at their disposal as well.

 

Edited February 21, 2022 by Spacescifi

[KSK]

I'm not following your reasoning here. Why would a hyper-diamagnetic slug make any difference?

Incidentally, superdiamagnetism is a thing. The slight catch is that the slug would need to be superconductive and maintain its superconductivity at whatever temperature it reaches inside the railgun. But hey - we're handwaving most of the engineering and materials science away here anyway, so why not.

Edited February 21, 2022 by KSK

[sevenperforce]

7 hours ago, Spacescifi said:

Hmmm... is there a way to artficially increase the diamagnetic properties of a material?

If so that could allow for multiple smaller railgun turrets with the OP velocity.

A change in diamagnetic properties won’t help with a railgun; the limiting factor for a plasma armature railgun is the compressive strength of the slug material.

If you’re going to do a coilgun, on the other hand, the magnetic field impulse is applied across the entire slug and so compressive strength is not an issue. There the issue is Ohm-induced heating due to eddy currents in the slug.

[Spacescifi]

8 hours ago, sevenperforce said:

A change in diamagnetic properties won’t help with a railgun; the limiting factor for a plasma armature railgun is the compressive strength of the slug material.

If you’re going to do a coilgun, on the other hand, the magnetic field impulse is applied across the entire slug and so compressive strength is not an issue. There the issue is Ohm-induced heating due to eddy currents in the slug.

 

Yeah I figured as much after I made that post. Who cares about the awesome rail gun if it is shooting out powder instead of slugs? I reckon the slug would be crushed into molten slag.... no... it would be crushed into plasma... which would dissipate fast over several kilometers.

 

So about the only thing an awesome OP plasma railgun could shoot is plasma... which won't have the OP range nor damage anyway.

However, if one combined a coil gun barrel and a hyper-diamagnetic slug (obviously fictional since it's extreme) then we could actually have OP turrets that won't need to be 800 kilometers long!

 

The more diamagnetic the slug the harder the coilgun barrel will shoot it for less Ohm heating/electrical power. It would work... so long we allow a suspension of disbelief for how in the world a slug was engineered to be so hyperdiamagnetic that a non-gigantic coilgun barrel can launch it at 30 seconds per lightsecond distance speeds.

[sevenperforce]

5 hours ago, Spacescifi said:

The more diamagnetic the slug the harder the coilgun barrel will shoot it for less Ohm heating/electrical power. It would work... so long we allow a suspension of disbelief for how in the world a slug was engineered to be so hyperdiamagnetic that a non-gigantic coilgun barrel can launch it at 30 seconds per lightsecond distance speeds.

Have you ever read anything from the Halo canon? You would enjoy it. They do all of this. 

[Spacescifi]

22 minutes ago, sevenperforce said:

Have you ever read anything from the Halo canon? You would enjoy it. They do all of this. 

 

No... I am spitballing ideas to see what could or not work. Very informative. Thank you.

[magnemoe]

On 2/19/2022 at 6:15 PM, Spacescifi said:

Hmmm... reality strikes again.

Why am I thinking the battleship would end up having a kilometer or several kilometers long railgun to achieve the required 30 seconds per lighsecond speed?

You would literally build the spaceship around the railgun, or simply attach it when in use and detach it when not in use.... leaving it to orbit somewhere in safe keeping with a fleet or station. Portable railgun... interchangeable between ships.

 

I guess this kills the multiple turret railgun idea for scifi I was thinking of... at least if I was going for maximum realism.... which I am not.

The scifi way to achieve multiple OP turret railguns would be to just use unobtanium materials with ridicously high melting points.

Yet it is still interesting to note how you would not be fooling anyone about what kind of spaceship you have if a several kilometers long spinally mounted railgun is mounted on it's nose.... which seems to he what reality dictates for the OP.

Small turrets cannot realistically do the OP withouut scifi make believe.

Well.. there is one way but it would involve pusher plates and nukes.... which would quickly be more expensive than the pellets being shot off by them.

 

That is an interesting idea though, using a shaped charge nuke to propel a bunch of shotgun pellets in space.

 

Still the idea seems plausible, downside with an spinal mounted gun is that you need to rotate your star destroyer sized ship to switching targets and makes dodging pretty easy. 
This has much of the same issue as projectile travel time. Now you could have limited traverse on it but an kilometre long gun has limited use in an fight, see it more for attacking fixed targets and perhaps putting down an sort of minefield moving trough space you would not want to get into, think suppressing fire, if you could launch larger payloads like bomb pumped x-ray lasers it would be even more useful in this rolle. 
As I understand coil guns are much more limited in velocity but they handle heavy stuff pretty easy like using them as carrier catapults. Still its limit how fast you can propel something small as you will need to switch magnets fast. 

[sevenperforce]

19 hours ago, magnemoe said:

downside with an spinal mounted gun is that you need to rotate your star destroyer sized ship to switching targets and makes dodging pretty easy. 

The Orbital Defense Platforms in the Halo universe have massive rocket thrusters which rotate the entire space station to allow them to aim the main gun. 

[Rakaydos]

though, at space combat ranges, the fine aim is more important that the gross turn speed. we're talking fractions of an arcsecond to accurately hit, not degrees per second to track.