Newtonian Aurora

[UnLimiTeD]

wut?

[Panopticon]

Mire: noun
1.
a tract or area of wet, swampy ground; bog; marsh.
2.
ground of this kind, as wet, slimy soil of some depth or deep mud.

I can only assume a mire control is some form of installation to produce or remove swampland, why this should be something specifically for Newtonian Aurora I do not know. I suppose it is possible there is a misspelling, but I think I am happy with my definition.

[Yonder]

All of your math is right, but we come to different conclusions, mostly because you assume a reasonable engagement range for shooting a Daring to be a million meters and I considered a reasonable range to be a million kilometers. At that point it becomes trivially easy to target planets and whatnot as well.

You (and others) have mentioned solar wind, third body gravity perturbations, etc as possible things to throw off aiming. Solar wind at the least isn't going to affect anything at all. Solar wind only effects modern satellites to appreciable levels in the long term, and satellites are very low-mass vehicles in comparison to most objects, and their solar panels gives them a fairly high surface area. This force would be completely negligible for a high density slug.

Now third body gravity is a completely different beast, you can't really make comments on how much it will affect a slug in all situations, because everything will depend so much on each specific trajectory and how close it passes to how many planets of what mass. That said, if you are not firing from a planets orbit, or at a planets orbit (/planet) and your slug doesn't go too close to a planet (within a few million kilometers) there once again wouldn't be a lot of difference.

Even if one of those things was true (and lets face it, it often will be, as most of what we are worried about is destroying shipyards, orbital habits, or attacking populations directly) those are the sorts of effects that are actually very easy to calculate. With close observations determining the masses of bodies from their orbital trajectories is easy stuff, and TN ships will have better sensors and computers than we do. Between visual observations and black body thermal release I'm thinking that the larger system bodies would be mapped within minutes of entering a system, even if  many moons took longer. Also the handwave for our active sensors is that they are somehow measuring the mass/gravity of objects directly, through the bend of space time or somesuch. I'm guessing that even in a handwaved "stealth mode" these active sensors would probably be able to pick out planets and moons right away.

Now, while that effect can be calculated, it is true that such affects do serve to expand the uncertainty of a projectile, because the forces on it are different depending on where it is, meaning that instead of smoothly increasing its distance from the target trajectory based on its initial inaccuracy, the rate of gaining inaccuracy increases. I suspect, though, that that effect will be very small, simply because our projectiles are moving very fast.

The scenarios that I am mostly worried about have some other caveats as well. I am not assuming that a ship is leisurely orbiting the Sun around Uranus and then firing 100 km/s shells. If that was the case there wouldn't be much worry, those (1 kg) shells are only hitting with 1.2 tons of TNT of force (5 GJ) and more importantly it will take something like 10 years of time for those projectiles to hit the earth. At those slow speeds third body gravity perturbations, etc, etc are very important, you'd probably still be hitting planets, but not shipyards. However I am more assuming the scenario where someone jumps in 10-20x past Pluto, then accelerates to a good speed of 15k km/s or something like that (or comes from warp at that speed, or comes into Pluto, then slowly moves away, then turns around to accelerate back).

If your projectile is moving at that speed it only takes 4 days for it to get to Earth, and while that sounds like a lot it doesn't affect the accuracy at all. As long as you aren't shooting super close to any planets you are in the clear. More importantly in that situation you aren't actually shooting at a target (say) 5e9 km away. The image of a cone of inaccuracy from a shot is only valid in the reference frame of the shooter. The shooter is shooting at where the target will be, if the planet is approaching him at 15k km/s and he shoots at 100 km/s then the projectile will be in flight for a little over 3.83 days. In that amount of time the projectile travels just over 33 million km. From the ship's perspective it's shooting at a target 150 times closer than it really is.

[bean]

I guess the accuracy debate comes down to what drift is more proportional to: distance or time.  Both will have an effect, but one is likely to dominate.
If drift is proportional to distance, then there is a fairly hard range ceiling.  This is the scenario JimiD describes.  It mostly includes pointing errors. 
Time drift is caused by things like the aforementioned gravitational perturbations, solar wind, and light pressure.  There are lots of things that can cause a body in space to drift, but the only one that would be of any real interest is third bodies, and those don't matter over short enough ranges.  At the sort of speeds we're dealing with, space can be approximated as flat with a very high degree of accuracy.
Distance drift will tend to dominate here, but I expect that we're looking at something at least an order of magnitude better then modern rifles.  They get microradian (~.2 arcsecond) accuracy with modern laser weapons.
As an aside shooting stuff in space is a good bit easier then on Earth.  There are fewer variables, and more can be computed ahead of time.  Things like perturbations can be compensated for with a good enough computer.  That's not to say I'm recommending unguided slugs for long-range work.  I'm saying that time drift causers like wind are less variable.
As another aside, I'm fairly certain that solar wind pressure is negligible compared to light pressure.  I've never heard of a physical solar wind sail.  Magnetic sails are another issue.

There are several ways of dealing with the RKV problem.  One is that, seeing as you have FTL sensors, RKVs are not as stealthy as they are in reality.  They're just very fast.  I've read that objects at relativistic velocity tend to give off hard radiation, which would foil attempts at stealth.  Another idea is to have the radiation surge upon leaving hyperspace roughly proportional to the speed.  That way, you can make an RKV, but it will be seen.
As for stopping one, if you throw a ball bearing at it, it will tend to die.  And if the ball bearing is off-center, the ablating RKV will push the rest off course.

[Yonder]

That's just it though, distance drift and time drift aren't different things, it's the same amount of drift for the same reasons. The only time they appear to be different is when you get your reference frame transformations wrong. Instead of thinking of the ship approaching the planet, and shooting at a planet 5 trillion kilometers away, think of a ship sitting motionless in space (which it is, from its frame of reference) with a planet 5 trillion kilometers away coming towards you. That ship isn't shooting at the planet 5 trillion kilometers away, it is shooting at where that planet is going to be, which is only 33 million kilometers away.

[bean]

That's just it though, distance drift and time drift aren't different things, it's the same amount of drift for the same reasons. The only time they appear to be different is when you get your reference frame transformations wrong. Instead of thinking of the ship approaching the planet, and shooting at a planet 5 trillion kilometers away, think of a ship sitting motionless in space (which it is, from its frame of reference) with a planet 5 trillion kilometers away coming towards you. That ship isn't shooting at the planet 5 trillion kilometers away, it is shooting at where that planet is going to be, which is only 33 million kilometers away.

I will admit that you are correct, so far as impecision in the physical pointing of the weapon is concerned.  However, that isn't where most of the error will lie in this case.  Most of the error will come from inaccuracies in where you choose to point it, which are going to be significant at half a light year.  Even if you're shooting at a planet, determining exactly where you are and how fast you're going relative to the planet is a significant task.  While you aren't terribly likely to miss your target, the planet may not be there when it hits. 
The same applies when you're at a more reasonable distance.  There's only one error that is proportional to the fraction of velocity the projectile travels on its own.

[Yonder]

That's not even a difficult task using today's technology.

[bean]

That's not even a difficult task using today's technology.

Precisely enough for weapons targeting?  At half a light year?  Over a short time period?  Mounted on a ship?
Really?
Maybe the planet example is overkill, but dismissing all pointing error as being in the physical precision of the laying of the weapon is wrong.  Other factors will come into play.  I can guarantee you that shooting at something 100,000 km away with a 100 km/s coilgun while going at 100 km/s is not the same as shooting at the same thing with the same coilgun at a range of 50,000 km while you're stationary.  Yes, the laying error is the same, but all the other variables are different.

[Yonder]

If your engines are on you would have more trouble due to ship vibrations. If your engines are off you are always stationary.

[bean]

That's not what I meant.  What I did mean (and I assumed it would be implied from context) is that you were stationary relative to the other vessel.

[Yonder]

That's not what I meant.  What I did mean (and I assumed it would be implied from context) is that you were stationary relative to the other vessel.

Why does it matter if your other target is moving, acceleration is the only thing that matters. If your target is moving at constant velocity you know where it's going to be, whether or not that constant velocity happens to be zero doesn't matter.

[chrislocke2000]

Why does it matter if your other target is moving, acceleration is the only thing that matters.

I would have to say I don't think that is entirely true. If either of you are moving relative to the other on anything but a head on or directly away from each other you are going to have more variables and inaccuracies to deal with ie:

- How good are your sensors in calculating exactly how fast you are going compared to one another?

- What about the time lag from sensors to gun control to turrets and accounting for that?

- What about the momentum built up by the turret itself as it moves to a firing solution and impac this has when stopping the turret?

- What about timing accuracy of exactly when you need to fire the round for the intercept?

- What about the consistency in the launch velocity of the round - does it change as the ship draws power to other systems that impacts the feed to the coil gun?

At the ranges we are talking about, moving v stationary is going to have an impact and for ship v ship a relatively big one. I therefore like the expectation of the mechnics that even when on a constant bearing and speed there is a chance of missing and when you get to more significnat range they are going to have to be smart rounds to help cope with the multitude of inaccuracies that will build up in the system v the theoretical position.

[bean]

Why does it matter if your other target is moving, acceleration is the only thing that matters. If your target is moving at constant velocity you know where it's going to be, whether or not that constant velocity happens to be zero doesn't matter.

You do understand that there is a limit to what sensors can determine, right?  Yes, assuming ideal circumstances, velocity doesn't matter.  But let's do some math:
Assuming the sensors are accurate down to 1 cm/s, and a flight time of 1 day (86,400 seconds).  The target will be off of its estimated position by about 864 m, assuming flat space.  That might be enough to hit, depending on the size of the target.  And the accuracy of said sensor will scale with distance.  Let's assume that we're shooting at a target that's stationary relative to us at 8.64 mkm with a weapon that has a muzzle velocity of 100 km/s, with the given sensor.  Our target position error radius is 864m, or 100 nradians.  But what if we approach the target with a velocity of 100 km/s relative, and launch at 17.28 mkm.  The flight time is the same, but now our velocity error is 2cm/s, and the target circle has a radius of 1,728 m.  If we look at that over launch distance, the angular error is the same.
The point of all this is simple.  There is going to be just as much if not more error built in from your sensors as there is from your gunlaying itself.  And to clear up any confusion, I use gunlaying to denote the precision with which your weapon can physically be pointed.

[Yonder]

You do understand that there is a limit to what sensors can determine, right?  Yes, assuming ideal circumstances, velocity doesn't matter.  But let's do some math:

That's all reasonable and  correct, but note that even in your situation velocity of the target doesn't matter. A 1cm/s sensor error will result in a 864m error radius regardless of whether one of the ships is moving with respect to the other or not.

I think that having two types of inaccuracies, sensor inaccuracies that depend on distance at firing time, and gunlaying inaccuracies that depend on the flight time of the projectile, would be reasonable mechanics, however I don't really see a mechanism that would degrade firing solutions based on the relative velocities, except of course for how the relative velocities impact the flight time.

Also the modelling of the sensor accuracy may be a good way to resolve the (odd IMO) issue with Thermal and EM sensors not giving targeting solutions. Maybe in Newtonian Aurora they each could, but the position and velocity accuracy of those passive sensors are an order of magnitude below an Active sensor of the same tech level.

I would have to say I don't think that is entirely true. If either of you are moving relative to the other on anything but a head on or directly away from each other you are going to have more variables and inaccuracies to deal with ie:

- How good are your sensors in calculating exactly how fast you are going compared to one another?

This is an issue whether your target is stationary or not, if your target is stationary with respect to you but your sensors have a velocity error margin that tells you that the target isn't stationary than you are in just as much trouble.

- What about the time lag from sensors to gun control to turrets and accounting for that?

That would be a very, very small time lag, and I have no idea why Steve would model it. That said it would be easily accounted for by the targeting software, as this time lag would be constant on a dedicated communications line, which I assume you would have between the Fire Control and weapons.

- What about the momentum built up by the turret itself as it moves to a firing solution and impac this has when stopping the turret?

There aren't any facings in Newtonian Aurora, so this doesn't have relevance for the game, in "real life" the same effect would happen when moving your guns to point at a stationary target, and this sort of conservation of momentum problem is accomplished by every one of our present day satellites with a reaction wheel every second.

- What about timing accuracy of exactly when you need to fire the round for the intercept?

This is a trivial problem to solve with pencil and paper to an arbitrary tolerance. It's not a time-consuming problem either.

- What about the consistency in the launch velocity of the round - does it change as the ship draws power to other systems that impacts the feed to the coil gun?

I'm assuming that the power activities of the main weapons are relatively isolated from the rest of the ship, the sort of electrical setup that would cause the other systems to interfere with firing would also cause firing the gun to interfere with the rest of the ship. This would be apparent right away, as the first shot fired would probably short out every electrical device on the entire ship.
Note that this is different from the power supplies of the ship being overtaxed such that the weapon capacitors are charged slowly, but that doesn't really seem to be a targeting problem.

[chrislocke2000]

This is an issue whether your target is stationary or not, if your target is stationary with respect to you but your sensors have a velocity error margin that tells you that the target isn't stationary than you are in just as much trouble.

But when you are both staionary you would not need to take velocity data from the sensors so that error would not be consistent.

In any case my previous list of points was not a list of things for Steve to try and model it was a simple justification as to why, when there is movement involved, your shots will be less accurate than when there is no movement involved; even when that is at a constant speed.