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Posted by: bean
« on: November 14, 2012, 04:52:49 PM »

If the rod is designed to punch through the atmosphere and can survive the heat of re-entry it does not need to be 20 tons.
Yes.  If it's a rod.  I was speaking of a projectile designed to make a crater and do surface damage.  Which has to be about the same in length and width.

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And impacting at hypersonic speed it will make a nice hole in the ground.
A rod will do little else.

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20 tons is absurdly high.  There is no physical reason for such a number.
It is somewhat high.  I made a mistake, and the actual number is more like 2.1 tons for tungsten.  It will be higher for other objects.
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We aren't talking about an arbitrary potatoe shaped object striking the atmosphere but a guided projectile.  Most of the energy is lost in the atmosphere and the end velocity of the projectiles is low, the less energy you give to the atmosphere (a more direct approach, a better areodynamic shape) the higher the impact velocity the lower the mass needs to be.  What it has to do is not disintigrate in the upper atmosphere like most meteors do.
Please do not lecture me on atmospheric entry and hypervelocity impact physics.  I've read far more about it that you have.  I know this because what you keep saying is wrong.  And I'm also willing to share the source of my insights.  For a basic background, check out Space Weapons, Earth wars. http://www.rand.org/pubs/monograph_reports/MR1209.html


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The material of the missile would vaporize on impact at those speeds, the plasma shock front of that would expand through the ship and tear it appart even if only a fraction of the momentum (1-10%) is transfered.  Thousand of KPS you don't gain by a warhead.
That's pretty much what I've been saying, although I think you vastly overestimate the amount of momentum transferred.  Stuff will break before it passes much on, and become part of the shrapnel cloud. 

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It doesn't need to be perfectly in-elastic since the ship is going to crumple around that impact point anyway, even if the plasma ball that used to be a missile punches through it the ship will be rendered mission killed since every human onboard will be reduced to so much thin paste.  Getting slamed into a wall at 100G isn't something you survive.
 
You've been doing the math as if the collision was perfectly inelastic (the objects stuck together).
But you still are ignoring my arguments as to why the momentum transfer won't kill the ship.  So I'll lay them out simply. 
First, the projectiles you keep using are ludicrously large compared to the target ship, particularly given their speed.  An Iowa-class was 33,333 times the size of its projectile at light load. 
Second, the ship's structure will not be able to take the forces involved in 100G acceleration.  The structure might be rated for 10G, but that's only from the engine.  From any other direction, it will fail under much lower loads.  The area that gets hit will behave more or less as a liquid, rip free very close to the projectile and turn into shrapnel (which is what I meant when I referred to spalling.)  The total momentum transferred to the rest of the ship will be minor.  The same goes for any other bulkheads it hits along the way, and the projectile goes out the other side as a cloud of plasma. 

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The point is putting a fusion bomb on a kinetic weapon moving at thousands of KPS is needless.  At those speeds you don't get spalling, or anything...6000 kps is 6,000,000 m/s that goes through a 100 m of ship in tens of microseconds.  Nothing can move out of the way of that, that is faster than the scale at which molecules move.  It might even be energetic enough to exceed the columb barrier but that is more akin to a particle beam hitting a material objec then what is normally considered an impact of two physical objects.
Not even close.  Particle beams operate close to c, which is 300,000 kps.  You're still a long way short of that.
And again, look at what happens here.  Force is equal to the change in momentum (impulse) times the change in time.  The time is very small (.000017 seconds).  The impulse available is simply too small to have a serious effect on the motion of either the projectile or the ship.  So no jelly.  Burned and lacerated humans, but not jellied.
Posted by: sublight
« on: November 14, 2012, 02:42:17 PM »

The classic weaponized long rod is designed for relatively low retry speeds, astronomically speaking. Say, 10 km/s. Add a couple zeros, and the mechanical forces of atmospheric deceleration will lead to structural failure in even a sold metal object. Once breakup starts retry heating adds insult to injury and transforms the object into an expanding ball of plasma. 20 tons at 10 km/s might hit the ground depending on shape and composition. 20 tons at 1,000 km/s won't.


I think Byron's point on jellifying the crew isn't that crew won't be jelly but rather that an impact that large is overkill since the ship could be broken apart by an impact an order of magnitude smaller.
Posted by: Paul M
« on: November 14, 2012, 01:29:46 PM »

If the rod is designed to punch through the atmosphere and can survive the heat of re-entry it does not need to be 20 tons.  And impacting at hypersonic speed it will make a nice hole in the ground.  20 tons is absurdly high.  There is no physical reason for such a number.  We aren't talking about an arbitrary potatoe shaped object striking the atmosphere but a guided projectile.  Most of the energy is lost in the atmosphere and the end velocity of the projectiles is low, the less energy you give to the atmosphere (a more direct approach, a better areodynamic shape) the higher the impact velocity the lower the mass needs to be.  What it has to do is not disintigrate in the upper atmosphere like most meteors do.

The material of the missile would vaporize on impact at those speeds, the plasma shock front of that would expand through the ship and tear it appart even if only a fraction of the momentum (1-10%) is transfered.  Thousand of KPS you don't gain by a warhead.  It doesn't need to be perfectly in-elastic since the ship is going to crumple around that impact point anyway, even if the plasma ball that used to be a missile punches through it the ship will be rendered mission killed since every human onboard will be reduced to so much thin paste.  Getting slamed into a wall at 100G isn't something you survive.  The point is putting a fusion bomb on a kinetic weapon moving at thousands of KPS is needless.  At those speeds you don't get spalling, or anything...6000 kps is 6,000,000 m/s that goes through a 100 m of ship in tens of microseconds.  Nothing can move out of the way of that, that is faster than the scale at which molecules move.  It might even be energetic enough to exceed the columb barrier but that is more akin to a particle beam hitting a material objec then what is normally considered an impact of two physical objects.
Posted by: bean
« on: November 14, 2012, 11:31:23 AM »

Kinetic kill weapons are as precise as the delivery mechanism.  You can use them at the level of taking out a city or removing an artillary position.  Brute force weapons such as asteroids are different matters but kinetic rods, or webs don't need to be all that large as the kinetic energy causes shock waves to radiate outwards.
No, there is a limit on the minimum size of kinetic projectiles.  They have to be long enough to penetrate the atmosphere, and the diameter is set by the structural requirements of the projectile.  Also, the damage of a kinetic depends on its shape.  A long-rod will do most of its damage to what it hits, not to the surrounding area.  To get area damage, the projectile needs to have about the same length and width, which in turn drives mass up significantly.  The minimum size for such a projectile is likely to be about 20 tons.  Or you could break up the projectile above the surface, which would produce a fireball and shockwave.
Also, the projectile can't have terminal guidance, unless it dumps a lot of energy so that the plasma sheath goes away.

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The weapon speeds used in bog standard aurora don't need warheads the shock from one of them impacting on a ship would cause it to crumple and kill every living thing on it from blunt force trauma as they get hurled around inside.
No, it wouldn't.  The material they hit would shear off, and the projectile would probably go straight through.  Most of the damage would be from the ship's structure bouncing around.  This is not an inelastic collision by any stretch of the imagination.

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Consider also just for fun the impact of a 1000 kg missile moving at 6000 km/s on a 6000 tonne ship at rest.  The ship's new velocity would be 6000 km/s*1000 kg/(6000*1000)kg = 1 km/s assume this occurs in 10 ms.  The acceleration of the ship is 1000 m/s/0.01 s or 100,000 m/s^2 or 10,000 G.  The ship crumples around the impact point, and the crew is dead.  Warheads are pointless at these sort of velocities.
Warheads are pointless, but not because they turn the crew into jelly.  Think about it.  If the ship is designed to stand maybe 10Gs of acceleration, anything substantially above that will cause the structure to fail.  The vessel would still be dead because of spalling, but that's not the point.
Posted by: swarm_sadist
« on: November 14, 2012, 10:16:51 AM »

Just thinking of some ways to counter long range mass driver attacks while I wait. Some attributes of mass drivers:
-They need a large 'runway' to get moving
-It's target is fairly small
-A larger rock has more volume to burn than surface area to burn
-At very high speeds, p->kE

I notice:
-That a rock can be intercepted as it's accelerating, due to the large thermal signal it would generate
-That, if broken into smaller pieces, a rock is easier to both vaporize and move
-A tug could alter the course of even the most massive rocks at quite a distance
-Because mass approaches infinity near light, destroying mass is just as effective at reducing kE
-Even a slight deviation from course will cause a miss if far enough away
Posted by: Paul M
« on: November 14, 2012, 08:03:28 AM »

Kinetic kill weapons are as precise as the delivery mechanism.  You can use them at the level of taking out a city or removing an artillary position.  Brute force weapons such as asteroids are different matters but kinetic rods, or webs don't need to be all that large as the kinetic energy causes shock waves to radiate outwards.

The weapon speeds used in bog standard aurora don't need warheads the shock from one of them impacting on a ship would cause it to crumple and kill every living thing on it from blunt force trauma as they get hurled around inside.

Lets do the mass for the diamond:  100 ft = 30 m = 15 m radius volume = 14100 m3.  density is 3.5 g/cm3 or 3.5x10^3 kg/m3 mass = 49.4x10^6 kg.

At 0.01c we can ignore relativity and taking mass of planet as earth's mass you have a resulting velocity change of 3E6 m/s *49.4E6/6E24 = 24E-12 m/s (so the planet barely noticed this impact).  The K.E. is 9E12*25E6 or 1725E18 joules.  This is 1725 Gigaton's worth of explosive force.  However I found a nice web site the covered this and basically the results for 3,000 km/s impact as a non event at 1000 km from ground 0 since they think the object will break up in the air at a high altitude.

As a comparison a 1 km diameter iron asteroid at 17 km/s...  1000 m = 500 m radius volume = 522x10^6 m3 density of iron is 8000 kg/m3 giving a mass of 4176x10^9 kg.  negligable velocity change from impact.  The K.E. is 290x10^6*2075x10^9 = 6x10^20 J or about 1/3 of the above.  The effect on the earth would be significantly more castrophic as the object would strike the earth not break up in the air.

At .99c we get a resulting mass of the diamond projectile of 49.4x10^6*SQRT(1/1-(.99)^2)) or 350x10^6 kg.  Not quite enough to do to anything to the earths orbit as the momentum is only 10x10^16 so a change in the earths velocity of 10^-8 m/s...still the K.E. is 175E6*3E16 or 5E24 J (basicialy 5 million gigatons) and that is...well pretty impressive.  Assuming it can impact on the planet anyway.  Lets take 0.9 kJ/kg-K and see what the means...5E21J/(6E24*0.9) = an overall temperture rise of the planet by 0.001 K.  Lets consider instead 100 m diameter x 1000 m of rock (density 5.52x10^3 kg/m^3) = 43x10^9 kg of rock....so 5E21/(43E9*0.9) = well ok...that will certainly penetrate the crust.  After that I imagine half the planet becomes unlivable rather fast.  The object is moving to fast to fragment in the atmosphere I'd think so its energy loss there will likely be rather small.  The planet itself though is going to be there..probably with a new axial tilt and a lot of siesmic activity.

Consider also just for fun the impact of a 1000 kg missile moving at 6000 km/s on a 6000 tonne ship at rest.  The ship's new velocity would be 6000 km/s*1000 kg/(6000*1000)kg = 1 km/s assume this occurs in 10 ms.  The acceleration of the ship is 1000 m/s/0.01 s or 100,000 m/s^2 or 10,000 G.  The ship crumples around the impact point, and the crew is dead.  Warheads are pointless at these sort of velocities.
Posted by: sublight
« on: November 14, 2012, 07:27:50 AM »

Nice to see this thread's final conclusion receive 3rd party confirmation from xkcd.

A 100ft diamater diamond would mass roughly 50kTons. Six posts ago jseah speculated that 10kTons moving at 0.33c would be needed to crack the crust. If the Xkcd numbers are good, then cracking planets is even harder than our dreadnought-sized missile assumptions.
Posted by: liq3
« on: November 14, 2012, 02:19:43 AM »

You don't need to get to . 99c though.  That'd be a planet killer.  0. 01c would be enough to do massive localized damage. 

Also it's 100foot, not m.
Posted by: swarm_sadist
« on: November 13, 2012, 07:30:55 PM »

I don't think you seem to understand, liq3.

Check the density of diamond, then check how much mass a 100m diameter ball has. Next, determine how much energy it would take to reach anything remotely close to .99c, then determine what sort of energy it would take in game. Try to design a ship that can do this with end game tech, 'try' being the key word.

While everyone just cranks up the numbers to justify kinetic weapons, at those energy levels I could just build a giant laser than could vaporize the crust. That way I would not have to wait for my space rock of solid diamond to accelerate at the target, wouldn't need to aim the weapon from far away, and would not have to worry about any mass in the way to alter it's course or slow it down.
Posted by: liq3
« on: November 13, 2012, 10:14:29 AM »

hxxp: what-if. xkcd. com/20/

tl;dr.  A 100-foot diameter diamond hitting earth at . 99c would punch it's way to the mantle and probably end all life (at the very least cause mass extinction). 
Posted by: bean
« on: February 23, 2012, 12:44:20 PM »

My knowledge of cobalt bombs (or any other types of salted nuclear weapons) suggests that they aren't terribly effective.  For one thing, they definitely don't leave all property undamaged.  For another, the half-life is long enough that you probably won't get much out of it either.  The half-life is 5 years, so if it is intense enough to kill everybody, I'm not going in for a couple decades.
If you wish to kill off a planet, kinetics are the best option.  For scenarios when you only want a small area, slow kinetics or nukes work well.  Visible lasers do, too.  Maybe Steve could add those.  It would make specialized bombardment craft useful.

Expensive though.  Planet-cracking costs way too much energy, like building a dreadnought sized missile.  2.7 fuel-mass ratio on a 10kton engine will be 27ktons of fuel... which is 27 million litres.  Very expensive even by TN aurora standards.  Easier to use a boat load of kinetic missiles to scour the surface.  Or just plain old-fashioned nukes and dirty bombs.
I was thinking about unlikely scenarios, such as strong enough defenses that only your dreadnought-sized missile can get through.  In that case, cracking the planet is a side-effect of destroying your enemies.  Not likely, but possible.
And that list was mostly in jest, anyway.  Not something that's going to happen very often, certainly not often enough to bother coding in.
Posted by: Mel Vixen
« on: February 23, 2012, 12:16:36 PM »

Well if you get enough particles into the air you could force a "nuclear" winter or you could destroy the ozon-layer with something more vicious then CFCs but both arent neither fast nor economical convenient. Rocks are cheap if we still could use massdrivers. Goldbombs would work althought you would need a few hundret to level a planet which makes me wonder what damage it would do to the ecosphere.
I would try to target food-sources thus the plantlife of a planet to kill its inhabitants if i have Bioweapons at hand. If i would have to kill Earth i would target Bees and other polinating insects. On the other Hand/paw/pod/claw/tentacle (or whatever your species has) you could add your own invasive lifeforms for example simple algae or grasses to a planets ecosphere. This can have interresting effects, take the first mosses on earth, they caused a Iceage on theyr first appearence.
 
Man i hate to plan Planetwide genocides, on those scale everything behaves like freaking coackroaches.
Posted by: jseah
« on: February 23, 2012, 07:18:07 AM »

1. It's the easiest way to remove said biologicals.
Expensive though.  Planet-cracking costs way too much energy, like building a dreadnought sized missile.  2.7 fuel-mass ratio on a 10kton engine will be 27ktons of fuel... which is 27 million litres.  Very expensive even by TN aurora standards.  Easier to use a boat load of kinetic missiles to scour the surface.  Or just plain old-fashioned nukes and dirty bombs. 

A 10kton impact at 100kkm/s relative though (5E22 J).  =D  Everything on the planet is dead.  Probably lose a good chunk of the crust and atmosphere. 
Practical, no.  Makes a point, that it does.  (we can do this and we are not afraid to use it.  Don't piss us off)

For least property damage, I think the cobalt bombs mentioned will beat anything else.  Kinetic missiles are just not good at precision work.  Neither are nukes, I might like to mention. 
Posted by: ollobrains
« on: February 22, 2012, 09:19:25 PM »

And then u would need some form of GFFP counter as well i get the general idea.  Well lets see what our MIA programmer has to say when he wakes up
Posted by: Arwyn
« on: February 22, 2012, 09:16:04 PM »

If your looking to actually crack the planet, kinetic is probably the way to go, but it would have to be big and fast.

If your just looking at icing a city, or disposing of obnoxious biologicals, then nukes/radiological weapons are the way to go. Its faster, cheaper, and from a strategic perspective a much easier weapon that say a tailor made biological weapon. They also don't tend to mutate like a biological might.

Cobalt bombs for example, are intensely radioactive, but the half like only around 5 years. If you don't like waiting that long, there are other types of radiological/nuclear fallout weapons that have even shorter durations.

Sodium-24: 15 hours
Gold-198: 3 days
Tantalum-182: 115 days
Zinc-65, 245 days

Of course those half lives are only for the isotopic materials, and are generated by a regular nuke, which is going to leave a LOT of regular radioactive contamination around. In theory, these isotopic nukes were small yield but intensely radioactive for short durations. Kill the bad guys and then roll into town a week later, is more less what they were designed for. Nobody has actually BUILT one, but the theory is there.

From a game perspective though, it might be a bit too much like GFFP. Also, some aren't exactly practical. Sodium has unpleasant reactive qualities that make it challenging to handle, and gold is a bit too pricey to be lobbing it around in mass produced nuclear weapons.

The other problem is that while the intense gamma ray emitters die off fairly quickly, the remaining isotopes from the blast are still present and due to the decreased yield and blast radius, could be possibly more concentrated in a smaller area.

You COULD use the current genetics research tree do do a biological warhead, and the idea has gotten used in a couple of games (thinking Sword of the Stars in particular) but the RESEARCH costs and time to do a tailor made bio-weapon for an alien race you dont have much info on is going to be huge.

Once again, you start getting into GFFP, which Steve hasnt been really thrilled about in the past, and the other problem, is that if the NPR's get to use them like players, they WILL use them. Unless of course Steve feels inclined to do a lot of AI coding to factor in racial militancy or xenophobia before the NPR gets weapons release for the bad stuff....
Either way,