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> I bet with a bit of clever tech you can pull off some insane over-the-horizon railgun shots. The projectiles would only have the force of gravity/terminal ve

> I bet with a bit of clever tech you can pull off some insane over-the-horizon railgun shots. The projectiles would only have the force of gravity/terminal velocity behind them unless they have been able to create an explosive railgun projectile (that doesn't explode on the launchpad due to the extremely high temperatures and other shock railguns apply to their projectiles). > Laser having +- zero flight time should solve most of that. I think "most of that" is a little overly optimistic. Target tracking is a complex problem, particularly in a war-like scenario where the target might very well be supersonic and in less than ideal weather conditions. Anti-ship missiles can and are designed to travel below radar range, so trying to get a good sense of depth against a blue sea and white/blue horizon is far from trivial even for a computer. The laser still might be the "least bad" defensive weapon against anti-ship missiles, but the whole thing is far from full-proof. We haven't really seen a full on naval conflict between two modern navies, so we kind of forget just how amazing most of the weapons are these days.

njharman 13y ago
> The projectiles would only have the force of gravity/terminal velocity Horizontal velocity will, presumably, be reduced by drag. But it won't be zero for a long, long ways over the horizon.
- UnoriginalGuy 13y ago
  Not sure I follow. You point the projectile too low and it just hits the ocean (due to the curvature of the earth), you point it higher than the horizon then the projectile will continue to travel upwards indefinitely until it runs out of energy and then will fall back to earth with the force of gravity. The only way what you're saying works is on a flat planet or against a target within your horizon.
  - Filligree 13y ago
    It will still be travelling sideways when it hits the target, and unless your target is a long, long way off it'll be travelling sideways with significant speed. Railgun projectiles, like cannon shells, travel on a parabolic curve - not a half-circle.
    - UnoriginalGuy 13y ago
      Cannon shells cannot be fired over the horizon either. Firing over the horizon will convert the projectile's forward momentum into height, it will reach whatever its apex is, run out of momentum and then fall due to gravity. The angle is just too steep. The only way to make this an effective weapon is to fill it with explosives (since then you've just created a mortar). But firing explosives from a railgun has its own issues. Most weapons which depend on a steep parabolic curve to hit their targets also have explosives in them, like artillery, mortars, ICBMs, etc. You can use a less steep curve to deliver blunt force to a target (catapult, cannon, gun, etc) but these weapons have a finite range as the earth is curved, therefore you'd have to tilt them too far back to overcome that, which will cause all that lovely forward force you're depending on to do damage going up into the sky as it flies higher and higher.
      - Filligree 13y ago
        I'm going to assume that the designers have considered this, and that even though it's over-the-horizon the projectiles will still have significant momentum when they hit.
      - vilhelm_s 13y ago
        You seem to be saying that in order to fire a projectile farther, one needs to make launch angle closer to vertical. But that is not the case, unless the distances get very large you always achieve the longest distance by firing at a 45 degree angle, so half the velocity is in the horizontal direction. Making it more vertical than that will make the range shorter. For extremely large distances (probably not relevant for naval railguns), the curvature of the earth becomes significant. But the correction goes in the other direction, it is optimal to fire at an angle more horizontal than 45 degrees. In the limiting case, the optimal angle for an ICBM is 22 degrees [1], and they will re-enter the atmosphere more horizontal than veritical [2]. [1] http://www.fas.org/rlg/garwin-aps.htm http://www.fas.org/rlg/garwin-aps.htm [2] http://www.fas.org/nuke/guide/usa/icbm/Slide92.JPG http://www.fas.org/nuke/guide/usa/icbm/Slide92.JPG
        UnoriginalGuy 13y ago
Havoc 13y ago
>I think "most of that" is a little overly optimistic. Target tracking is a complex problem I disagree. The current complexity of target tracking comes mostly from that fact that you need to work out firstly where the thing is, secondly where its heading (in 3 dimensions & in real time) and third how fast. Having a +- zero flight time means you only need to do the first step. You can always rinse & repeat if its a laser pulse. Essentially its the difference between hitting a moving car with a tennis ball and hitting a stationary car with a tennis ball. Thats why I think it would solve "most of that". Obviously if the laser isn't a pulse(s) then you're back to square one.
- ChrisOstler 13y ago
  That assumes that aiming the laser is instantaneous, too. I have no idea if that is the case or not.
  - Havoc 13y ago
    >That assumes that aiming the laser is instantaneous, too. I was simplifying quite a bit & making assumptions yes. Another slightly sketchy assumption is that the laser fires instantly...chances are there is some kind of power up delay.
Symmetry 13y ago
I'd assume that even with a laser they'd do most of the targeting work with a radar, in which case it's pretty easy to distinguish the target from the background. Just look at the Doppler shifts of the returns and don't worry about anything that isn't moving with respect to the radar. Missiles might indeed hide below the horizon on their approach, but that makes them just as invisible to visual ship-based detection as it does to radar.
- UnoriginalGuy 13y ago
  Anti-ship missiles are designed specifically to make for small radar cross-sections and to fly below radar range.
  - Symmetry 13y ago
    Yes, but "below radar range" in this context means below the horizon, which even from the top of a ship is only 15 km away or so. At mach 4 a Sunburn can cover that distance pretty quickly. I'm sure the low radar visibility make a big difference when hiding from AWACs on the approach, but since radar returns scale with the fourth power of distance I don't see how a missile could possibly have such a low cross section as to be invisible at as close a range as 15 km.

njharman 13y ago

> The projectiles would only have the force of gravity/terminal velocity Horizontal velocity will, presumably, be reduced by drag. But it won't be zero for a long, long ways over the horizon.

UnoriginalGuy 13y ago
Not sure I follow. You point the projectile too low and it just hits the ocean (due to the curvature of the earth), you point it higher than the horizon then the projectile will continue to travel upwards indefinitely until it runs out of energy and then will fall back to earth with the force of gravity. The only way what you're saying works is on a flat planet or against a target within your horizon.
- Filligree 13y ago
  It will still be travelling sideways when it hits the target, and unless your target is a long, long way off it'll be travelling sideways with significant speed. Railgun projectiles, like cannon shells, travel on a parabolic curve - not a half-circle.
  - UnoriginalGuy 13y ago
    Cannon shells cannot be fired over the horizon either. Firing over the horizon will convert the projectile's forward momentum into height, it will reach whatever its apex is, run out of momentum and then fall due to gravity. The angle is just too steep. The only way to make this an effective weapon is to fill it with explosives (since then you've just created a mortar). But firing explosives from a railgun has its own issues. Most weapons which depend on a steep parabolic curve to hit their targets also have explosives in them, like artillery, mortars, ICBMs, etc. You can use a less steep curve to deliver blunt force to a target (catapult, cannon, gun, etc) but these weapons have a finite range as the earth is curved, therefore you'd have to tilt them too far back to overcome that, which will cause all that lovely forward force you're depending on to do damage going up into the sky as it flies higher and higher.
    - Filligree 13y ago
      I'm going to assume that the designers have considered this, and that even though it's over-the-horizon the projectiles will still have significant momentum when they hit.
    - vilhelm_s 13y ago
      You seem to be saying that in order to fire a projectile farther, one needs to make launch angle closer to vertical. But that is not the case, unless the distances get very large you always achieve the longest distance by firing at a 45 degree angle, so half the velocity is in the horizontal direction. Making it more vertical than that will make the range shorter. For extremely large distances (probably not relevant for naval railguns), the curvature of the earth becomes significant. But the correction goes in the other direction, it is optimal to fire at an angle more horizontal than 45 degrees. In the limiting case, the optimal angle for an ICBM is 22 degrees [1], and they will re-enter the atmosphere more horizontal than veritical [2]. [1] http://www.fas.org/rlg/garwin-aps.htm http://www.fas.org/rlg/garwin-aps.htm [2] http://www.fas.org/nuke/guide/usa/icbm/Slide92.JPG http://www.fas.org/nuke/guide/usa/icbm/Slide92.JPG
      - UnoriginalGuy 13y ago

Havoc 13y ago

>I think "most of that" is a little overly optimistic. Target tracking is a complex problem I disagree. The current complexity of target tracking comes mostly from that fact that you need to work out firstly where the thing is, secondly where its heading (in 3 dimensions & in real time) and third how fast. Having a +- zero flight time means you only need to do the first step. You can always rinse & repeat if its a laser pulse. Essentially its the difference between hitting a moving car with a tennis ball and hitting a stationary car with a tennis ball. Thats why I think it would solve "most of that". Obviously if the laser isn't a pulse(s) then you're back to square one.

ChrisOstler 13y ago
That assumes that aiming the laser is instantaneous, too. I have no idea if that is the case or not.
- Havoc 13y ago
  >That assumes that aiming the laser is instantaneous, too. I was simplifying quite a bit & making assumptions yes. Another slightly sketchy assumption is that the laser fires instantly...chances are there is some kind of power up delay.

Symmetry 13y ago

I'd assume that even with a laser they'd do most of the targeting work with a radar, in which case it's pretty easy to distinguish the target from the background. Just look at the Doppler shifts of the returns and don't worry about anything that isn't moving with respect to the radar. Missiles might indeed hide below the horizon on their approach, but that makes them just as invisible to visual ship-based detection as it does to radar.

UnoriginalGuy 13y ago
Anti-ship missiles are designed specifically to make for small radar cross-sections and to fly below radar range.
- Symmetry 13y ago
  Yes, but "below radar range" in this context means below the horizon, which even from the top of a ship is only 15 km away or so. At mach 4 a Sunburn can cover that distance pretty quickly. I'm sure the low radar visibility make a big difference when hiding from AWACs on the approach, but since radar returns scale with the fourth power of distance I don't see how a missile could possibly have such a low cross section as to be invisible at as close a range as 15 km.