|
Post by omnipotentvoid on Jun 28, 2017 6:14:31 GMT
utilitas : not to mention the fact that these coils may have function under high acceleration forces when a ship or drone with strong engines is dodging
|
|
|
Post by matterbeam on Jun 28, 2017 18:33:56 GMT
Wouldn't a high vacuum effectively act as an unpolarized dielectric material? Ablation could be solved by not making it a vacuum. You could make a hybrid coil/railgun, where the coils are used only to keep an asymmetric projectile (a combination of a paramagnetic or antiferromagnetic material and a diamagnetic) oriented in line with the axis of the barrel. Then you'd just fill the barrel with a suitable atmosphere prior to firing (no need for an end seal) and propel the projectile through the conductive atmosphere. Ablation would still exist, but be severely diminished due to all the plasma being guided by the coils as well. But there comes one major issue when approaching significant fractions of c. Coil switching. A railgun has no active components except for the flux wave down its rails, but a coilgun has to switch its coils on and off. You would need to use progressively smaller and smaller, thinner and thinner coils as the projectile speeds up, otherwise you risk losing quite a lot of efficiency to residual inductive flux - in the best case scenario. Worst comes, the projectile will spin out as the coils are unable to switch back off in time and misalign. Those coils could get extremely small, and therefore extremely fragile. I don't think this is a good solution. You are replacing ablation through friction heating by aerodynamic heating. A conductive atmosphere just means the current can jump across the rails along the entire length of the rails, shorting out the circuit above and below the projectile and reducing the Lorentz force to zero. Coil switching is an engineering issue that will definitely be resolved. There are ways to significantly reduce the residual flux using superconductors, and there are techniques which particle accelerators use to push particles to relativistic velocities.
|
|
utilitas
Junior Member
I can do this all day.
Posts: 59
|
Post by utilitas on Jun 29, 2017 12:36:24 GMT
I don't think this is a good solution. You are replacing ablation through friction heating by aerodynamic heating. A conductive atmosphere just means the current can jump across the rails along the entire length of the rails, shorting out the circuit above and below the projectile and reducing the Lorentz force to zero. Coil switching is an engineering issue that will definitely be resolved. There are ways to significantly reduce the residual flux using superconductors, and there are techniques which particle accelerators use to push particles to relativistic velocities. Current tends to conduct along paths of least resistance. Tends to, most of the time in atmospheric mediums. It's better to use aerodynamic ablation rather than friction ablation because: A. Given a constant input of atmosphere, any ablated material gets carried out the barrel along with the projectile at similar speeds. With plain friction there's a higher possibility of backing up and uneven wear. B. The atmosphere, when entering plasma state, will expand dramatically. Ionized plasma tends to conduct well, but any short-circuits would theoretically drive the projectile further through added pressure. Whether that pressure can travel fast enough and induce enough momentum to aid the projectile is a thing for the spreadsheets, though. But if it can, it's like combustion for the space age. An atmosphere-aided railgun would likely need segmented rail switching similar to that of a coilgun, effectively removing one of its advantages, but such are the costs of trying to lob a grain of sand hard enough to carve straight through a small moon.
|
|
|
Post by Enderminion on Jun 29, 2017 13:41:30 GMT
of course the easy way would be to use a misile to get up to high speed then fire you're blast launchers, I have one missile that spits out 42 armoured one megaton bombs
|
|
|
Post by RiftandRend on Jun 30, 2017 6:45:07 GMT
of course the easy way would be to use a missile to get up to high speed then fire you're blast launchers, I have one missile that spits out 42 armoured one megaton bombs The easy way to what? Get a projectile to high speed?
|
|
|
Post by RiftandRend on Jul 1, 2017 12:05:45 GMT
I made a more realistic weapon. It has a much larger projectile and far lower muzzle velocity. This should not suffer as much projectile ablation as the previous railguns.
|
|
|
Post by RiftandRend on Jul 1, 2017 12:21:40 GMT
of course the easy way would be to use a missile to get up to high speed then fire you're blast launchers, I have one missile that spits out 42 armoured one megaton bombs I disagree. Missiles have limited Delta-v (NTRs) or acceleration (MPDTs). This limits the velocity and/or minimum range of a missile launched KKV. In comparison, a railgun/coilgun can achieve all its acceleration almost instantly and does not have to work against the rocket equation to achieve high velocities.
|
|
|
Post by ross128 on Jul 1, 2017 14:21:27 GMT
Technically the rocket equation does apply, it's just that you're using a multi-kiloton warship as reaction mass for a sub-gram projectile. Your mass ratio is probably fine, and you're only worried about maximizing exhaust velocity (known in this situation as recoil).
|
|
utilitas
Junior Member
I can do this all day.
Posts: 59
|
Post by utilitas on Jul 1, 2017 14:34:15 GMT
Technically the rocket equation does apply, it's just that you're using a multi-kiloton warship as reaction mass for a sub-gram projectile. Your mass ratio is probably fine, and you're only worried about maximizing exhaust velocity (known in this situation as recoil). Less rocket equation and more conservation of momentum. That's like using Lorentz transformations and trigonometry to calculate the speed of two objects.
|
|
|
Post by omnipotentvoid on Jul 1, 2017 14:34:56 GMT
Technically the rocket equation does apply, it's just that you're using a multi-kiloton warship as reaction mass for a sub-gram projectile. Your mass ratio is probably fine, and you're only worried about maximizing exhaust velocity (known in this situation as recoil). Exactly. We want speeds aproaching c or at least a good fraction of c. And we want short acceleration times to boot. While a rocket has the advantage to accelerate for some time, allowing for exhaust velocites well below the target speed of the final projectile, those exhaust velocities would still be in the hundreds of kilometers a seceond. Rockets like this simply do not exist. Thus it is not feasible to use rockets to achieve the desired speeds.
|
|
|
Post by matterbeam on Jul 1, 2017 15:46:39 GMT
Technically the rocket equation does apply, it's just that you're using a multi-kiloton warship as reaction mass for a sub-gram projectile. Your mass ratio is probably fine, and you're only worried about maximizing exhaust velocity (known in this situation as recoil). Exactly. We want speeds aproaching c or at least a good fraction of c. And we want short acceleration times to boot. While a rocket has the advantage to accelerate for some time, allowing for exhaust velocites well below the target speed of the final projectile, those exhaust velocities would still be in the hundreds of kilometers a seceond. Rockets like this simply do not exist. Thus it is not feasible to use rockets to achieve the desired speeds. For realistic targets accelerating at realistic rates, you can use much slower projectiles to catch them than relativistic rounds. You can further reduce the required round velocity by predicting the path the target will take, or by firing multiple rounds to cover multiple routes.
|
|
|
Post by omnipotentvoid on Jul 1, 2017 16:04:32 GMT
Exactly. We want speeds aproaching c or at least a good fraction of c. And we want short acceleration times to boot. While a rocket has the advantage to accelerate for some time, allowing for exhaust velocites well below the target speed of the final projectile, those exhaust velocities would still be in the hundreds of kilometers a seceond. Rockets like this simply do not exist. Thus it is not feasible to use rockets to achieve the desired speeds. For realistic targets accelerating at realistic rates, you can use much slower projectiles to catch them than relativistic rounds. You can further reduce the required round velocity by predicting the path the target will take, or by firing multiple rounds to cover multiple routes. By "we want speeds aproaching c" I meant that this thread is about achieving projectile velocities approaching some large fraction of c by lowering projectile mass.
|
|
|
Post by ross128 on Jul 1, 2017 16:19:06 GMT
Oh I know, I was mostly making a joke about how the rocket equation is really just another way to calculate conservation of momentum (which is why its variables are essentially mass and velocity).
It's just that one of the variables (the mass ratio) is so extreme that it's convenient to ignore it to simplify the equation.
But yes, in principle you can increase projectile velocity nearly indefinitely by reducing the projectile's mass. If you introduce a net charge to the projectile, you could also use a cyclic accelerator (because of how electric charges interact with magnetic fields) to essentially curl up a long barrel into a small space.
At which point you've built a charged particle cannon.
If you use two barrels, one positive and one negative, you could theoretically fire them in such a way that the launched particles attract and neutralize each other shortly after leaving the barrel in order to effectively create a neutral particle cannon.
|
|
|
Post by Enderminion on Jul 1, 2017 16:55:44 GMT
effectively create a neutral particle cannon. or just make an actual neutral particle cannon
|
|
|
Post by matterbeam on Jul 1, 2017 22:19:00 GMT
For realistic targets accelerating at realistic rates, you can use much slower projectiles to catch them than relativistic rounds. You can further reduce the required round velocity by predicting the path the target will take, or by firing multiple rounds to cover multiple routes. By "we want speeds aproaching c" I meant that this thread is about achieving projectile velocities approaching some large fraction of c by lowering projectile mass. I see. Nevertheless, there is no practical reason for using relativistic projectile to catch spaceships. There may be other reasons, but not this.
|
|