Author Topic: Impact Physics  (Read 9174 times)

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Offline Bremen

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Re: Impact Physics
« Reply #15 on: January 28, 2012, 04:36:09 PM »
Yeah, given the numbers it seems like the relative speed of vessels will have a *much* larger effect on damage than the rating of the weapon itself.

The way to fix this, I think, would be to keep the energies the same but use much smaller projectiles. Instead of a 4800 kj Railgun launching a 1kg chunk, it could launch a 1g chunk. This would result in much higher launch velocities with the same level of energy in the impact, and make the speed of the vessel only likely to double the damage at most, rather than increase it a hundred fold. Also make kinetic weapons much less of a knife fight compared to the scales of everything else.

It does make it seem odd that it's not going through the armor like a needle through a piece of cloth, but combat wouldn't be very fun if everything was one shot one kill.
 

Offline UnLimiTeD

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Re: Impact Physics
« Reply #16 on: January 28, 2012, 07:27:47 PM »
Well, the first goal of newtonian aurora seems to be making it realistic, not playable.^^
So the question arises, at these speeds, why wouldn't I just open a tank releasing a few tons of 100 gram metal balls, then turn around and decelerate?
It'll result in a shrapnel-cloud a few hundred meters in diameter going at the target area at still 3k km/s, and being noticeably harder to evade.

I suppose this is a point where a bit of gameplay would be useful, but then again, we have no data yet on the actual hitrates, but be below 1%.
 

Offline blue emu

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Re: Impact Physics
« Reply #17 on: January 28, 2012, 08:04:20 PM »
At these relative velocities, just bleeding out a cloud of air or water (=> ice crystals) should be enough to wreck anything that flies through it.

Mass drivers could defend the inner system just by tossing clouds of gravel up into the path of approaching ships.
 

Offline fcharton

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Re: Impact Physics
« Reply #18 on: January 29, 2012, 03:28:57 AM »
So the question arises, at these speeds, why wouldn't I just open a tank releasing a few tons of 100 gram metal balls, then turn around and decelerate?

These would spread very fast (like the square of the distance travelled). Against a moving ship, at some distance, the probability of a hit would be very low. The same goes for a railgun, by the way. All the above discussion seems to be proving (and this pretty much was Procyon's point on the Newtonian Aurora thread), that at any relative velocity over 100km/s, a hit is a kill.

This means, past a certain level, there is no point in producing a more powerful railgun, with a higher velocity. It also means the 'angular precision' of the gun will limit its range, and that this range will increase linearly with angular precision and target dimension.

So, at short distance, mutual destruction is assured. Railgun create a kind of exclusion zone around their ships. The interesting question, then, is whether lasers and other energy weapons will be worth researching...

At longer range, what matters is being able to estimate target trajectory. For small and non ballistic objects, like ships, this makes railguns almost inefficient.

Francois
 

Offline jseah

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Re: Impact Physics
« Reply #19 on: January 29, 2012, 05:52:56 AM »
This means, past a certain level, there is no point in producing a more powerful railgun, with a higher velocity.
You mean there is no point to producing railguns that shoot anything but 1kg shells. 

Faster muzzle velocity means the 1kg chunk of iron has a higher delta-v relative to your ship and allows you a larger set of fire solutions. 

It might be plain impossible given certain relative velocities for your ship to shoot his ship with a railgun.  This is most evident in a flyby shooting of static targets. 


Scenario: your ship is doing a flyby shooting of defences around a planet.  You know the defender's design of railgun and thus there is an "exclusion" zone around their planet you must not enter or their guns will hit you.  Since you are not static, your ship can hit them while they can't hit you. 

As you approach at interplanetary distances, your maximum range is limited by angular precision and target dimension. 
Once you are doing the actual flyby, your muzzle velocity plays the largest factor in the maximum deviation angle the shot can have from your current flight path (ie. you shoot the 1kg shell directly perpendicular to your flight path) and thus your minimum range. 
Thus only between the maximum and minimum range will you ever have a firing solution. 

So the maximum range is limited by your accuracy.  Minimum range is limited by muzzle velocity.  A bigger railgun can keep firing for longer and thus hit more targets. 
 

Offline fcharton

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Re: Impact Physics
« Reply #20 on: January 29, 2012, 06:48:26 AM »
Since you are not static, your ship can hit them while they can't hit you. 

Is that correct? Since everything is ballistic (ie moves at constant speed), and since only range (and angular precision of the railguns) matter, everything should be sym├ętric, no? In other words, the math should be the same in the ship frame and the planet frame, both galilean, no?

Of course, a ship could course and speed, and therefore dodge projectiles it detected. This would result in a lower to-hit probability.

A bigger railgun can keep firing for longer and thus hit more targets. 

I see your point. But would such "low angle solutions" be penalised by the longer distance to target? In 3D space, for a fixed angular precision, dispersion should vary as the square of the range. It should be worse in practice, since precise target acuqisition will be a decreasing function of range. Somehow, I have the impression that increases in velocity will bring very little gain...

Francois
 

Offline jseah

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Re: Impact Physics
« Reply #21 on: January 29, 2012, 09:58:33 AM »
Yes, your ship can jink and make course corrections to avoid shots.  The distance at which you can't do this anymore is what I would call the exclusion zone. 

------------

You mean high angle solutions?  Coz as you approach your minimum range, the angle the railgun shell makes with your intended flight path (your actual flight path won't be a nice line) increases. 

And target acquisition gets easier as you approach your minimum range.  Since, well, you're closer. 

Muzzle velocity has much less impact on your maximum range against statics.  It has a *massive* impact when using railguns vs mobiles. (since time of flight restricts your accuracy against mobiles relative to their delta-v; this error is likely to huge and will swamp everything else when you are far away)

In any case, I would not say that muzzle velocity is useless.  Your railguns always need to play catch up with your engines.  (or more precisely, *their* engines)
 

Offline byron

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Re: Impact Physics
« Reply #22 on: January 29, 2012, 01:43:30 PM »
Well, the first goal of newtonian aurora seems to be making it realistic, not playable.^^
So the question arises, at these speeds, why wouldn't I just open a tank releasing a few tons of 100 gram metal balls, then turn around and decelerate?
It'll result in a shrapnel-cloud a few hundred meters in diameter going at the target area at still 3k km/s, and being noticeably harder to evade.

I suppose this is a point where a bit of gameplay would be useful, but then again, we have no data yet on the actual hitrates, but be below 1%.
Because with the sort of drives avaliable here, a few hundred meters across is easy to dodge at any range where the launching ship can survive.

Is that correct? Since everything is ballistic (ie moves at constant speed), and since only range (and angular precision of the railguns) matter, everything should be sym├ętric, no? In other words, the math should be the same in the ship frame and the planet frame, both galilean, no?

Of course, a ship could course and speed, and therefore dodge projectiles it detected. This would result in a lower to-hit probability.
Absolutely.  Any reference frame works, and the relative velocity is the same in either ship-centric or planet-centric.  The thing is that the ship can break off after launch, which, if far enough out, should allow it to avoid action.
This is Excel-in-Space, not Wing Commander - Rastaman
 

Offline fcharton

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Re: Impact Physics
« Reply #23 on: January 29, 2012, 02:05:33 PM »
The thing is that the ship can break off after launch, which, if far enough out, should allow it to avoid action.

True, but in that "railgun vs railgun" example, wouldn't the reasoning go like this :
1- railgun to-hit probability are a function of range (the square of it, if we're in 3D, this, btw, is a real problem with a 2D aurora...)
2- therefore, the best launch site is when the flyby ship has the shortest trajectory to target
3- this would be known to the target, who can now send (in advance) a hail of projectiles on the ship final approach
4- in this setting, evasive maneuvers after launch become useless, the incoming ship could avoid this either by launching earlier, but then, longer ranges means lower to hit pb, or by 'wiggling' while it flies by

I find this last point interesting : somehow, we are assuming that, in NA, fuel is spent to accelerate, but in fact, in "combat mode" (ie wherever you might be target) perhaps we should consider ships spend fuel at all time to make minor trajectory changes, in order to avoid enemy guns... And the closer the enemy might be, the more precise its guns, the more you need to wiggle while you fly.

Francois
 

Offline Bremen

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Re: Impact Physics
« Reply #24 on: January 29, 2012, 05:00:52 PM »
Under no circumstances should railgun shots be 100% certain kills. It might be realistic, but it makes for lousy gameplay.
 

Offline chrislocke2000

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Re: Impact Physics
« Reply #25 on: January 29, 2012, 05:01:14 PM »
I think this just highlights how much you are going to need to reduce your closing speed with any ships you want to engage with rail guns or who are defending themselves with rail guns. I can see plenty of situations where a single missile hit may well take out the ship. It will be interesting to see how this plays out.

If this does make the game somewhat unplayable I suspect we will need to have far stronger shields that project a lot further out from the ship and angled to force more glancing blows.
 

Offline jseah

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Re: Impact Physics
« Reply #26 on: January 29, 2012, 05:23:39 PM »
2- therefore, the best launch site is when the flyby ship has the shortest trajectory to target
It's railguns!  It fires 1kg shells!

1 ton of ammo is very little weight on a ship and 1000 rounds is far more than enough. 

You just spray and pray.  As fast as you can as long as you have firing solutions.  Just that the firing solutions for the static defense is far worse than for the incoming ship due to the ship jinking its course. 
 

Offline fcharton

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Re: Impact Physics
« Reply #27 on: January 29, 2012, 05:50:47 PM »
You just spray and pray.  As fast as you can as long as you have firing solutions.  Just that the firing solutions for the static defense is far worse than for the incoming ship due to the ship jinking its course.  

And I would disagree with you. Spraying is certainly the way to go, esp since ships are small and can evade.
But...
In a 3D world, projectiles will spread over a spheric cap, the surface of which grows as the square of range. This means that if you double range, your probability to hit is divided by 4 (knowing that with large slugs, 1kg or the like, hit==kill)

As far as efficiency is concerned, a high rate of fire at close range will always beat a longer 'firing window'.

Francois
« Last Edit: January 30, 2012, 08:14:31 AM by fcharton »
 

Offline fcharton

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Re: Impact Physics
« Reply #28 on: January 29, 2012, 05:52:52 PM »
I think this just highlights how much you are going to need to reduce your closing speed with any ships you want to engage with rail guns or who are defending themselves with rail guns.

Either slow down, or line up... I mean, if you can line up and fire straight ahead, you don't care about speed.

Francois
 

Offline blue emu

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Re: Impact Physics
« Reply #29 on: January 29, 2012, 08:06:57 PM »
In a 3D world, projectiles will spread over a spheric cap, the surface of which grows as the square of range. This means that if you double range, your average distance between projectiles (and therefore your probability to hit) is multiplied by 4 (knowing that with large slugs, 1kg or the like, hit==kill)

At double the range, the average distance between projectiles is x2, not x4... isn't it? It's the area of the spherical shell section over which they are spread that increases x4.

Your to-hit probility drops by a factor of 4, yes... but that's because the to-hit probility is proportional to the inverse square of the projectile spread, not because the projectiles themselves spread exponentially.
 

 

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