Newtonian Aurora

[bean]

I tend to be skeptical by nature also, so this is not a problem for me.  Do all the research you want.  I can only talk from what I have seen and worked on.  I don't know how much data is available on some of the EFPs from the IEDs in Iraq, as the military was pretty good on confiscating any cameras or notes that were on the soldiers around if it involved penetration of the armor on an M1.  But data on the APDS penetrators the M1 (ok, most any NATO 120mm smoothbore) fires is fairly easy to get ahold of.  It would do just as well as an example of what happens to a chunk of material striking armor at a few km/s.  Turns molten as it punches through and then 'detonates'.  Easier to find and just as much a proof of concept.

That's not what I was skeptical about.  I'm skeptical that copper on an artillery shell behaves at all like an APDS.  I'd think it gets torn to pieces by the blast, and just adds some shrapnel.

[Five]

I would just like to add on the copper shaped charge. It is very dangerous, after enough tours in Iraq and afghan it is one of the most feared ieds and we have had plenty of lectures/training videos on them. As for findinding info on the public side I remember future weapons on the discovery channel doing a few things that used cone shaped copper to punch through metal...should be easy enough to find.

-Five

[Yonder]

Not sure how you get that 38 million kelvin. To me, a thousandth of 5GJ means 5MJ, tungsten has a specific heat of 170 joules per kg.K, so you'd get an increase of about 29 000 K, no? The millions would be if all the kinetic energy is turned into heat.  This said 1/1000th is probably a very low value, and a few percent of kinetic energy turned into heat would heat the slug to a million degrees...

Yeah my thermodynamics is rusty, let me go through step by step.
Molar heat capacity is 24.27 J/mol/K, There are 183.84 kg in a mol of Tungsten, so the specific heat is .132 J/kg (this seems to be where we differ, where did you get 170 from?)
Heat of fusion is 35.3 kJ/mol, so 192 J/kg, and heat of vaporization is 806.7 kJ/mol, so 4388 J/kg. We know everything will be vaporized, so first we take out the heats of fusion and vaporization, which leaves us with 4,995,420J left (so honestly the heats of fusion and vaporization didn't matter, but I had to check first, and now that we've done the math we may as well use it). That remaining energy heats the projectile to 37.84 million Kelvin.

[bean]

I would just like to add on the copper shaped charge. It is very dangerous, after enough tours in Iraq and afghan it is one of the most feared ieds and we have had plenty of lectures/training videos on them. As for findinding info on the public side I remember future weapons on the discovery channel doing a few things that used cone shaped copper to punch through metal...should be easy enough to find.

-Five

I am familiar with the concept of a shaped charge, and that of the EFP.  I'm not questioning that either exists, or that EFPs were used in IEDs.  I'm skeptical of Procyon's statement that a piece of copper on an artillery shell makes a good penetrator.

Yeah my thermodynamics is rusty, let me go through step by step.
Molar heat capacity is 24.27 J/mol/K, There are 183.84 kg in a mol of Tungsten, so the specific heat is .132 J/kg (this seems to be where we differ, where did you get 170 from?)
Heat of fusion is 35.3 kJ/mol, so 192 J/kg, and heat of vaporization is 806.7 kJ/mol, so 4388 J/kg. We know everything will be vaporized, so first we take out the heats of fusion and vaporization, which leaves us with 4,995,420J left (so honestly the heats of fusion and vaporization didn't matter, but I had to check first, and now that we've done the math we may as well use it). That remaining energy heats the projectile to 37.84 million Kelvin.

You have a three orders of magnitude here.  The molar mass of Tungsten is in fact 183.84 grams per mole, not kilograms.  The projectile only reaches about 37,000 kelvin.

[UnLimiTeD]

It's pretty certain the copper makes a good penetrator, but why does it not fragment on acceleration?. I suppose this is what byron is asking.
If we expect it to melt and spread when hitting the tank, decelerating from X->0, then shouldn't it already do that when accelerating from 0->X?
We can expect the projectile in the railgun be come close to the point of melting already.
It will have to be a rather durable material, though, as it MUST not spread in the launcher.
Might damage the ship, and terrible for accuracy.
Like using a Flamethrower as Artillery.

[Yonder]

It's pretty certain the copper makes a good penetrator, but why does it not fragment on acceleration?. I suppose this is what byron is asking.
If we expect it to melt and spread when hitting the tank, decelerating from X->0, then shouldn't it already do that when accelerating from 0->X?

Because the acceleration from X->0 is orders of magnitude higher than 0->X? Also the acceleration from 0->X is applied on the entire rear of the projectile (and maybe even along the sides if the sabot is very tight) while the acceleration from stopping will all be on the contact point, so until the round is already greatly deformed the pressure on the round will be even more orders of magnitude higher on impact.

We can expect the projectile in the railgun be come close to the point of melting already.
It will have to be a rather durable material, though, as it MUST not spread in the launcher.

A railgun (but not a coilgun) may indeed be shooting a molten or close to molten projectile. For very long shots it may cool down before firing, but I'm guessing most shots will be against targets less than 10 seconds out, so it will indeed still be very hot.

The railgun projectile really won't spread in the launcher, this isn't a gun, it accelerates the round through magnetic forces that apply nearly equally for all parts of the slug. It won't be as uniform as the Coil Gun, because a Railgun projectile will have friction along the sides, but the railgun will obviously be designed to minimize that friction, and if you toss that force then all molecules of the slug will accelerate uniformly.

Now if you are trying to do tricky things like fire a non-conductive round via a conductive sabot, or launch a non-uniform material that doesn't have uniform conductance and hence magnetism (like something with control mechanisms) then you will have enormous forces involved, but for a simple slug you won't have many internal forces.

[fcharton]

Molar heat capacity is 24.27 J/mol/K, There are 183.84 kg in a mol of Tungsten, so the specific heat is .132 J/kg (this seems to be where we differ, where did you get 170 from?)

Got the 170 here http://www.engineeringtoolbox.com/specific-heat-solids-d_154.html . I believe it explains the difference between my 29 and you 38. The magnitude difference is as Byron said: molar mass is in grams not kilograms, so you get a specific heat of 0.132 J / kg K, whereas it should be 132 J/kg K.

Welcome to the 1e3 club, Yonder, got myself there too a couple of posts above !

Francois

[procyon]

I am familiar with the concept of a shaped charge, and that of the EFP.  I'm not questioning that either exists, or that EFPs were used in IEDs.  I'm skeptical of Procyon's statement that a piece of copper on an artillery shell makes a good penetrator.

It's pretty certain the copper makes a good penetrator, but why does it not fragment on acceleration?. I suppose this is what byron is asking.

Ummm....

I guess if the question is why doesn't the copper turn into a bunch of shrapnel... I don't know.  

I was always looking at what it did.  The fact it hit as a mass was a given.  I didn't worry about that, just what the effects on the vehicles were and what could be done.  There may have been sites where it fragmented and failed to penetrate, but I didn't look into our sucessful stops, just the failures.

I know that the copper wire in our fragmentation grenades has to be pre-serated to achieve uniform fragmentation.  But why it works so well strapped to 70 year old artillery shells...?  I honestly don't know.

But why copper makes a good IED EFP really doesn't have anything to do with Aurora, so I am going to let those interested follow this one up on their own if they are curious.

EDIT

I don't normally use Wikipedia as a reference, but there seems to be decent info there with a fair number of sources listed that should be easy enough to check on EFPs.  Here is the link if anyone wants to do the actual homework.  I didn't read it through, but hope it is helpful.  At least it is easy to reach.

http://en.wikipedia.org/wiki/Explosively_formed_penetrator

EDIT 2

And from the picture, it looks like the copper is actually on the end of the artillery/mortar shell (probably the base?).  My apologies on that.  When I got to the sites they could tell what the explosive charge was by the remaining fragments, but the shell itself was long gone so I never actually saw it intact.  WWII artillery shell plus couple kgs of copper always seemed to = a ruined vehicle and dead crew.
The question wasn't so much how they did it, as they already knew how and it worked.  The question was what could we do about it.

[chrislocke2000]

But why copper makes a good IED EFP really doesn't have anything to do with Aurora, so I am going to let those interested follow this one up on their own if they are curious.

I suspect that it actually comes from the other side of the equation as an EFP it works and that's good enough rather than it being particularly good v other materials, as a material that is readily available, relatively easy to shape and is forgiving on impurities I would see it as a winner in an environment where the logistics for the user have a lot of challenges.

[bean]

So it's an EFP based off of an old artillery shell.  That makes so much more sense.  From you initial statement, it sounded like artillery shell plus copper chunk plus duct tape equals dead tank.

[procyon]

So it's an EFP based off of an old artillery shell.  That makes so much more sense.  From you initial statement, it sounded like artillery shell plus copper chunk plus duct tape equals dead tank.

I never needed to worry about the fine details of how the IED was made, and each was generally different so it wouldn't have helped much.  It is pretty much an old artillery shell with clips or tape holding a chunk of copper water pipe someone hammered out to shape.  You can work copper with a blow torch, and it isn't terribly hard, so it doesn't take much to make any old piece of copper into a plate.  It seemed that so long as they could get the stupid thing secured to a chunk of explosives the d@*ned things would cut through whatever was in the way and then turn into a fireball on the far side.

But this has wandered a bunch.  All I was hoping to show was that a chunk of metal moving at 'slow' velocities for the game we expect is very good at tearing through substantial protection and destroying a target - as opposed to punching through.  If I was going to spend the money to send my shells into space, I would make sure they didn't just pass on through the target. 

[Steve Walmsley (OP)]

Is there any plan to reduce the number of forced 5sec increment over those many-days engagements?

As in Standard Aurora, there are only forced increment lengths when missiles are being launched or about to hit their targets. There are no forced increments when they are in flight.

Steve

[Steve Walmsley (OP)]

Upon thinking about it, maybe instead of "minimum travel time" a "maximum proportion of journey spent accelerating" would be better. Spending the whole trip accelerating is fastest, but not by much, and very inefficient.

I am coming to a similar conclusion based on testing. I keep changing max fleet speeds for a geosurvey fleet, depending on whether it is moving from Jupiter to Saturn, or operating within Saturn's moons, or moving within the inner planets. So far this has varied from 100 km/s to 2000 km/s for the same ship. To reduce micromanagement, what I need is a more intelligent way to set max deltaV used for a particular journey, especially when the ship is operating mainly on default orders, such as for geological survey.

Perhaps a combination of the portion of journey under acceleration and max speed, with the lowest speed taking precedence. Or maybe base it on distance rather than portion of journey so I can set a max speed at the start of the journey and won't need to track time passed.

Steve

[Steve Walmsley (OP)]

Steve
Nice to see the armour ratings going up and am eagerly looking forward to more instalments on your test campaign, a couple of other random thoughts:

- Are you thinking of tracking rail gun ordnance now? Was wondering what sort of usage of ammo there would be in long slow approaches where you might be firing continuously and if this may now be enough to start worrying about magazine and weight requirements. This might also have more of an impact on fighters.

- Any more thoughts on maximum effective speeds for ships due to the dangers of impact from space debris? I could see this as being more of an issue when it comes to moving around asteroid belts.

The jury is still out on rail gun ordnance. Maybe to prevent continual firing, an easier option may be some type of failure chance for a weapon.

I have been looking at cosmic dust and the speeds that would be required for significant damage. Based on the size and mass of cosmic dust particles, the speed required to damage armour is a lot higher than I would have expected. It probably wouldn't be worth it for the early to middle game, except in Nebula systems. On the other hand, there isn't a huge amount of material available on this subject so if someone has knowledge in this area please speak up.

Steve

[Steve Walmsley (OP)]

I've added some extra TG conditions in the format: "Fuel less than 20% + Required Decel". This will trigger the condition as True when the ship has an amount of fuel that is less than 20% of its maximum fuel capacity plus enough fuel to decelerate to rest from its current speed. There are similiar conditions for 10%, 30% and 40%.

A new Conditional Order of: "Create Fuel Warning Event" has also been created. This condition just generates an event message but takes no further action.

With the complexities involved in Newtonian Aurora, a simple "Move to the Nearest Colony for Refuelling" conditional order may no longer be appropriate (although it is still available) so this new event generation alerts the player to a potential issue and the player can then decide what action to take.

Steve