Newtonian Aurora

[Steve Walmsley (OP)]

Which is why I think Newtonian combat will be dominated by fighters, or at least parasite vessels.  You could have a mothership with a high efficiency cruise drive, plus all the non-combat components; extra fuel tanks, maintenance storage, etc.  Then when combat threatens it launches a bunch of fighters and cruisers, which with their low efficiency drives and less weight spent on secondary systems could massively outmaneuver comparable non-parasite vessels.

I think is a real possibility. The other reasons I think fighters or small parasites will be common are cost and weapon effects. Firstly, it is possible that in a battle you may have to commit to a course toward the enemy in order to close the range and once on that course you will have a limited ability to pull away again. In that case, an 'expendable' launch platform would constitute a more acceptable level of risk than a major warship that would be hard to replace. Secondly, in an environment where a single nuke can take out a capital ship, you would probably want the enemy to expand high yield weapons on relatively low-cost and harder to hit targets.

Steve

[Steve Walmsley (OP)]

Have to say I can't wait to have a go at this myself. Already started building the brownie points with the wife in the anticipation of some long evenings locked in the study!

Was just having a quick look at the rules again and noticed that the costs in warhead between conventional / nuclear / nuclear laser seem quite small to me and was wondering if these differences should be more pronouced to give players more of a decision to make in the types of ordinance used?

Also, having re-read the rail gun thread I was not sure if Steve was going to be calculating kinetic energy for damage based purely on the exit velocity of the shell or the eventual relative impact velocity when it hits. I'm assuming it's the later with the exit energy just being used to calculate total enegry requirements and cool down requirements.

Just running some numbers I can see that even with a closing speed of just 500kms any shots are going to be lethal: By my calcs that would give an impact energy for a 1 kilo slug of 125k MJ, more than enough to punch through basically any armour and shields and go back out the other side. I'm wondering how that sort of narrow but very high damge will be dealt with for internal systems.

Laser warheads are larger as well as more expensive, which means the missile will have less acceleration. That will be a factor as well as cost. Conventional warheads will be mainly for RP situations in a multi-Earth start.

At the moment a railgun round penetrates armour and then expends all its remaining energy inside the target. I haven't definitely decided if this final yet so its possible I might have an exit hole as well and not have all the energy expended inside the target. I really don't know enough about the subject yet so I'll finalise this once I find some relevant materials to study.

Steve

[Steve Walmsley (OP)]

I wish I could say the same thing.  Convincing my wife and kids to put the RPGs and Starfire on hold so I can play is a hurdle I am not looking forward to.  

I am fairly sure he intends to use actually impact speeds, not launch speeds.  I wouldn't think it would be hard to code for, but I am not a programmer.  

The damage modeling for slugs could really use some attention.  My reasons....

At those velocities, unless this slug is made of some incredibly resilient material it won't survive impact intact.  If it could, we need to be using whatever it is made of for armor.  The energy generated will create an enormous amount of heat (depending on velocity at impact) - likely vaporizing the slug and turning it into a violently expanding mass of superheated gas and particles.  It is going to become a bomb.

The slugs fired from the 120mm on our tanks only hits targets at < 3 km/s.  Often less than 2 km/s.  They turn into molten slag on the way through the armor and essentially detonate in the target.  Check the records.  I saw a fair number of enemy vehicles hit by our tanks - the only exit holes were on soft vehicles.

The railgun slugs will likely be hitting at higher than single digit km/s.  The penetrator (if it overcomes the armor) won't be intact.  It will be a 'fireball'.


EDIT

On the thought of a slug hitting a shield, I really don't have any idea what would happen.  I don't really know what the shields are.  If they are some distance from the ship, they may yaw the slug.  This would ruin its sectional density as it struck and profoundly limit its penetration.  If the shields are nearly flush with the ship, then I doubt it makes much difference.

I will use impact speeds - not launch speeds - so moving very fast when someone is firing railguns is only a good idea if you don't get hit

Useful information about current anti-tank rounds. That is how the kinetic strike code works at the moment.

Shields are very close to the ship (unlike my earlier assumptions). At the moment, they are modelled simply as removing 'energy' from the lasers and railgun projectiles. In the latter case that effectively means slowing them down before they hit.

Steve

[Steve Walmsley (OP)]

Now, this raises an interesting question about missiles, and "explosive rounds" (if such things exist). Should they be fragmentation or "pure energy" weapons? (or maybe a combination of both)?

At the moment I have coded conventional warheads, which are impact only, plus bomb-pumped lasers and standard nukes, which are area effect. I plan on a solid warhead - in effect the same as a railgun round but with a mass in tons rather than kilograms - and you really wouldn't want to run head-on into one of those at speed, plus a fragmentation warhead that splits into perhaps a thousand one kilogram chunks. Also not a very pleasant prospect.  You will likely be able to set a dispersion rate for the latter (I am assuming a small explosive charge to provide 'sideways' momentum), so while the forward motion of the projectiles will be the same as the original missile, the rate at which the 'width' of the projectile cloud increases over time will be preset during missile design. Obviously the speed at which the 'width' increases will be far less than the forward momentum.

I have upped the ship armour strength a little so it ranges from 100 MJ per 'box' at level 1 tech up to 1500 MJ per box at level 12 tech. Even so, battles in Newtonian Aurora are likely to be extremely brutal and seeing the enemy first is going to be vital.

Steve

[Steve Walmsley (OP)]

Personnally I think all missiles should have a 'kinetic' setting.  Just don't arm the warhead.  Shrapnel will likely look like a railgun when it hits, unless the fragments are very large.  But a missile with a 4 ton warhead releasing 4000 - 1kg chunks of metal could be a real terror as it approached a group of ships.  Will make 'dodging' difficult. 

There could probably be a distinction for a pure kinetic kill weapon.  A 1kg projectile hitting a target at km/s will vaporize into a bomb like weapon.  A 1000kg chunk of metal probably won't.  Might fragment.
But with the energy it will contain the shockwave it should create will make the issue of 'will there be a hole in the back' more of a 'will there be a big enough piece left to identify the exit hole'.

I wrote the previous reply before reading this post

Either of the above is going to make life extremely difficult for the target

Steve

[Steve Walmsley (OP)]

As far as i remember a past discussion about this, steve will have them be deleted if they miss their target and theres currently nothing in the future path.
But if the target is in front of a planet, that planet will be hit.

That is the plan at the moment. I'll clean up projectiles and out of fuel missiles when there is nothing for them to hit.

Steve

[Steve Walmsley (OP)]

As it stands it seems to me that there will actually be very little point in adding armour to your ships, better to spend the weight on increasing your acceleration or Delta V reserves so you can get out of the way as there is a good chance that any hit is going to be lethal irrespective of the armour you have.

Just looking at Steve's example of each armour block having 125MJ damage resistance, if we say a pretty well armoured ship has ten layers that does not give much protection on point hits at all compared to the numbers being tossed around.

I do think that is a valid design choice. Although in Newtonian Aurora you will get about twice the armour thickness for the same tonnage as you do in Standard Aurora, so ships will be able to carry a significant amount of armour.

Steve

[fcharton]

I have no idea either. Perhaps the speed of sound of the gas would be a suitable approximation?
Of course that requires the knowledge of the temperature of the material, which would also have to be approximated somehow.

Speed of sound would be too slow (a few hundred metres per second, most explosives have detonation velocities of several km/s).

I've been thinking about it, not very efficiently, school was a long time ago...

Normally, apart from thermal radiation (which is electromagnetic and therefore propagates at the speed of light), the "heat wave" would move according to Fourier law. That is to say, heat transfer over time would be proportional to surface, times temperature gradient, divided by distance.

If you imagine heat exchange between two concentric spheres (the "slug" and some reference radius in the ship), you have something like
dQ/dt = 4 PI k r1 r2 (T2-T1)/(r1-r2), where k is medium conductivity, ri the radii of the spheres, and Ti the temperatures.

You could derive the temperature by assuming a fraction of kinetic energy gets converted into heat (and an average specific heat), but if the projectile vaporizes, we're talking of a gradient of several thousand degrees, which should result in a very brutal heating of its surroundings.

Yet, I doubt this is the relevant factor. No matter how fast the heatwave, the ship is pretty much dead if the projectile vaporizes inside, and probably safe if it does outside. The matter, then, would be how long it takes for the slug to heat, melt and vaporize...

Francois

[LoSboccacc]

On the other hand, my experience with the limited missile engagements I have tried so far indicate that missile flight times could be on the order of days for some battles rather than minutes or hours.

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

[Yonder]

Speed of sound would be too slow (a few hundred metres per second, most explosives have detonation velocities of several km/s).

Not speed of sound in air at sea level, speed of sound of the substance involved (in this case superheated duranium, or tungsten, or lead, or something).

I believe that the definition of an explosion (as opposed to just a fast burn) is that the expansion is faster than the speed of sound in the medium it is exploding in, but I also thought that that detonation velocity was directly based on the speed of sound of the explosive as it burned. As in the speed of sound of the super heated gases the explosive formed immediately after firing.

Unfortunately while there are a lot of examples of exhaust velocity, but far fewer for explosion temperature, so I can't put that assumption to the test. There would be an additional complication because there is a coefficient (the ratio of specific heats) that is (mainly) determined by the form of the gas, ie Monatomic, Diatomic, etc. While there are many tables available for this coefficient for common gases, I am sure that finding coefficients for the more complicated molecules often formed by an explosion, for example the (CH2-N-NO2)3 + 3CH2(ONO2)2 + NH4NO3 + 3H2O created by C4, would be more difficult. It would still be possible to do in principle though, in simpler explosives that yielded smaller molecules.

If that method was used for modelling the expansion of a slug that last part wouldn't be a concern for solid elemental metal projectiles, as they would sublimate as Monatomic Gases.

As an example for this method, lets say that a 1kg slug of tungsten hits a ship at 100km/s. This collision has 5GJ of energy. We'll posit that a thousandth of this goes into heating the slug at the instant of impact. If the projectile started at perfect zero then after heating it would be turned into a cloud of tungsten gas with a temperature of 37.83 million Kelvin (around twice that of the center of the sun). If I have done my rusty thermodynamics math right that comes out to a speed of sound of 53.3 km/s!

The last step is to check and see whether the assumption that gaseous cloud would actually disperse at it's speed of sound, and given the incredibly high speed of sound we just got I'm guessing it won't. In fact you can see this with a very cursory look, we got a speed half that of our starting speed (a quarter of the starting energy), by pulling out one thousandth of the energy at the start.

Ah, there is an even more direct way to get the average molecular speed from the temperature, which is actually directly defined from average molecular speed, I'm silly.

If you go that route you find that the average molecular speed of our tungsten gas is 2.27km/s.

Of course the problem with this whole method is that top choice: One thousandth of the energy goes into heating the projectile, it was completely arbitrary. I'm not really sure how we could choose an "accurate" number.

[Bremen]

I agree. Ships will definitely not be able to manoeuvre significantly in any short-time frame. It will be about positioning pre-engagment and making manoeuvres that could take several hours or days to complete. On the other hand, my experience with the limited missile engagements I have tried so far indicate that missile flight times could be on the order of days for some battles rather than minutes or hours.

Steve

If anyone's read the "Lost Fleet" series of novels (which I highly recommend), it features combat that resembles this. The basic strategy fleets employ is to maneuver in such a way that they "glance" past an enemy, making it so they can concentrate fire on a group of enemy ships can return fire is spread throughout their fleet; the better lead fleet then sails past and has several hours to recharge their shields/repair damage while the other fleet.. well, you can't fix ships that got blown up.

So this kind of combat might be a major advantage for shields. On the other hand, its starting to sound like railguns might be so lethal armor or shields wont help much against them.

Also, in response to the test campaign post, even with a million liters of fuel that's not a lot of delta-v (as is realistic). Surveying asteroid belts will be expensive early on.

I know there's going to be an option for maximum speed, but would you consider a "minimum travel time" option? Something to make sure a ship wouldn't burn full thrust to travel to a moon in 6 hours instead of a day. Might be useful for surveying those planets with a dozen moons.

Actually, did some quick math. At full load (for simplicity of math) leaving Earth and coming to rest at the moon would take 5.81 hours and burn 3,661 liters of fuel. The rest of the math is trickier and I'm not particularly knowledgeable, but using a quarter the fuel (915 liters) results in a flight time of only, by my sloppy math that would probably make a physicist scream, 13.74 hours.

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.

[fcharton]

Hi Yonder,

Very interesting comments. I believe you're right on explosion speeds.

As an example for this method, lets say that a 1kg slug of tungsten hits a ship at 100km/s. This collision has 5GJ of energy. We'll posit that a thousandth of this goes into heating the slug at the instant of impact. If the projectile started at perfect zero then after heating it would be turned into a cloud of tungsten gas with a temperature of 37.83 million Kelvin (around twice that of the center of the sun). If I have done my rusty thermodynamics math right that comes out to a speed of sound of 53.3 km/s!

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...

But even with this lower temperature gradient, I suspect that most of the damage would result from the electromagnetic energy and heat freed by this brutal increase in temperature, which would "roast" the ship before the gas had the time to explode.

And then, this temperature increase might make the fact the slug explodes into the ship or comes out of it irrelevant. I don't think a ship can survive the temperature increase caused by the collision (a million degrees even a few hundred km away is a lot of temperature).

But then, if the railgun was shot at close range, this would be true for the firing ship as well...

Francois

[UnLimiTeD]

For reference, the detonation velocity of nuke is ~400 km/s for gas expansion, and 550 km/s for implosion, based on earth like atmospheres.
These numbers should be sort of the upper limit for expansion, short of nuclear fusion taking place; keep in mind a nuke actually creates matter, as in, atoms split into more atoms that want to get away from each other.

So while we need to have a formula as laid out, we need slightly diminishing returns once to get to high 3 digit speeds, and if the ship is going at the shell with 5000 km/s, and it's structure can handle the shock, the shell would blaze right through, only leaving a part of it's energy within the ship.
There is no doubt that that part would still destroy the ship, but it might not utterly disintegrate it.

@ Steve, if you have energy Shields essentially as a form of Electric Armor, only against energy instead of kinetic, wouldn't it be interesting to have multiple shield types?
Like, having a force shield 50m away from the ship, but requiring enormous amounts of energy to keep up; One could have a battery ship to activate it for seconds before the next railgun barrage comes in.


Also, I'm starting to think that people will forgo small caliber, high muzzle velocity railguns, and just go for larger slugs, given that 50% of the speed in an average combat situation will come from the ship itself.

[procyon]

But then, if the railgun was shot at close range, this would be true for the firing ship as well...

Yes, I have wondered when throwing around nukes and high energy shells if a 'minimum safe distance' isn't something you would want to look at.  And having your own nuke chase down a ship closing on you could also turn out embarassingly.

(I am so looking forward to dealing with this.  I do hope it works out.)

I have said more than enough on what I feel will happen if you shoot a ship.  On the heat of the slug, when you compress mass it heats also, and it occured to me some time back (shortly after composing the thought that slugs probably look like cannonballs) that it is probably going to be molten when it leaves the railgun, or shortly there after.  If not molten, at least fairly close (depending on the material).  As I said, I would want a material that best deposited all of the energy into the target.

On the speed of expansion, this is one that I have argued with colleuges before.  The current formulas for shockwave propagation are less than ideal.  The don't always confirm experimental observation, so it truly is open to debate in some areas.  The rate that a wave can propagate through material can actually exceed the speed of light in certain mediums (which is why reactors glow, the electrons are exceeding the speed of light in water).  With the levels of energy and velocities we are talking about, we could get a large number of people arguing, but all should agree it would be fairly energetic.  

Whatever is easiest for Steve, is fine with me.  

I'm a tiny bit skeptical about this.  No offense, but anyone can say anything on the internet, and I find it hard to believe that a couple kilograms of copper is some sort of wonder penetrator.
As for penetration, there's a professor at my school who studies armor penetration and space debris.  I'm meeting him on the 26th, and will try to get some answers.

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.

EDIT
The example with copper was just to show that even a material that common can make a good kinetic kill penetrator.  (Actually, it is looking to become the material of choice in some EFPs).

You will likely be able to set a dispersion rate for the latter (I am assuming a small explosive charge to provide 'sideways' momentum), so while the forward motion of the projectiles will be the same as the original missile, the rate at which the 'width' of the projectile cloud increases over time will be preset during missile design. Obviously the speed at which the 'width' increases will be far less than the forward momentum.

Steve

You really don't need an explosive charge, and could control the dispertion rate fairly accurately with modern tech.  Just have the 'shrapnel' be 'sleeves' of cylinder like slugs.  Then have the missile begin to 'spin' as it releases the slugs.  It would be able to control the dispertion and density without the random accelerations of an explosive.  When done you could have a small explosive charge (a bit of left over propellent) shatter the remaining hull of the missile to add extra fragments to the center of the pattern.

If you had a ship nearby that could communicate with the missile, controlling the rate of dispertion might not be difficult 'on the fly'.  (Ok, sorry about the pun...)

If the missile was still accel/decel ' ing while releasing the slugs it could even create a 'cloud' with considerable length as well as width, in case you are intercepting a crossing target and having 'ordinance' in the target's flight path for a duration of time was important.

But this isn't a big issue for me.  You do this for free.  Whatever suits your fancy will work.  

As long as I get to try and blow up the 'bad guy' !!  

[chrislocke2000]

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.