Aurora 4x
VB6 Aurora => Newtonian Aurora => Topic started by: bean on January 26, 2012, 04:59:22 PM
-
I met with Dr. Schonberg today, and learned the following:
First, we have very little data on long rods (which I presume NA is using) at anything above ordnance velocities. This is for two reasons. First, it's difficult to run those tests. Second, nobody is launching long rods, and the chances of an object randomly functioning as one are very low.
That said, a couple things to add to the standard wisdom of atomic rockets.
While a projectile hitting a whipple shield will fragment, unshocked projectile will remain unitary and continue to penetrate. Long rods thus could go through multiple compartments, shedding length each time and destroying whatever is inside.
At velocities above about 30 km/s, the projectile begins to turn to plasma after impact. This could decrease penetration, as the plasma cloud will hit over a much larger area then a fragment of a projectile. This would tend to reduce penetration at these velocities, provided sufficient standoff is allowed. What that is, I don't know. Armor is effective against the plasma cloud. However, the same thing that was mentioned above could also occur, with multiple compartments penetrated.
To achieve either of the above, the long rod must hit straight on. Otherwise, the entire thing will disintegrate on the whipple shield.
-
First, we have very little data on long rods (which I presume NA is using) at anything above ordnance velocities. This is for two reasons. First, it's difficult to run those tests. Second, nobody is launching long rods, and the chances of an object randomly functioning as one are very low.
There is only one way to find out! Just donate me half a billion Dollars on my paypal account and ...
In all seriousness now isnt there some kind of Simulation-software for this kind of stuff? I know that some meteor-simulators allow to choose a form but i guess thats not compare-able.
I am not really convinced that Steves Railguns use Javelin like ordinance.
^^ maybe someone has contacts to the US Navy could get the info - after all they are building that Railgun prototypes for years now.
-
There is only one way to find out! Just donate me half a billion Dollars on my paypal account and ...
In all seriousness now isnt there some kind of Simulation-software for this kind of stuff? I know that some meteor-simulators allow to choose a form but i guess thats not compare-able.
I am not really convinced that Steves Railguns use Javelin like ordinance.
^^ maybe someone has contacts to the US Navy could get the info - after all they are building that Railgun prototypes for years now.
That's not the problem. The thing is that there is just no data to plug into the models. The Navy's railgun works at Mach 4-6, while we're talking Mach 25 and up. It's a completely different physical realm. And no, a meteor sim is not going to work.
-
So, the interesting question remaining is:
How much will turning into plasma decrease the effective velocity of the projectile?
Because the impact speeds are more likely to be in the range of 100km/s, so we can expect that to happen often.
Will it expand spherical? Aka, half the projectile will slow down significantly?
Will it disintegrate from front to back, thus significantly slowing down the rest of the matter?
We don't know.
-
So, the interesting question remaining is:
How much will turning into plasma decrease the effective velocity of the projectile?
Because the impact speeds are more likely to be in the range of 100km/s, so we can expect that to happen often.
Will it expand spherical? Aka, half the projectile will slow down significantly?
Will it disintegrate from front to back, thus significantly slowing down the rest of the matter?
We don't know.
Not that much. Plasma is what happens when the front of the projectile is under a couple hundred gigapascals or more that then go away.
No, because momentum is conserved, most of it will go into the ship. I'm not sure what the random velocity in plasma is, but it's not that high.
I think that it will not slow down the back significantly. The pressures involved are too high for the material to withstand as a solid, so the back section will probably be largely unaffected.
-
I haven't rally given much thought to the projectile shape. I assumed something like those fired by the US Navy Railgun, or a modern day APDS round
Steve
-
Well one can make some assumptions right? You [edit: i mean byron] say at high enough velocities our projectile turns to plasma, wouldnt that have a initial damage-profile compare-able to a very intense laserpulse due to the energy imparted on projectile and targed? Iirc some kind of Shockwave traveling through the matter or something?
-
If the projectile turns to plasma, then you could consider that most of its kinetic energy is turned into heat and consider most/all damage results from two causes : electromagnetic shock and heatwave.
I'm not sure how one would calculate the electromagnetic shock, but we discussed the heat aspect with Yonder in the NA thread. Assuming a specific heat for the projectile and a speed will provide an impact temperature. Heat transfer equations would then define an expanding sphere of decreasing temperature, which, if you cut it to some "tolerable level" would sort of define the radius of the "hole" the projectile would melt in the ship.
This said, I wonder whether the "turn into plasma over 30 km/s" rule applies in space. Air friction, and pressure, play a considerable role in heating fast moving objects. Would the same happen in space?
Francois
-
If the projectile turns to plasma, then you could consider that most of its kinetic energy is turned into heat and consider most/all damage results from two causes : electromagnetic shock and heatwave.
I'm not sure how one would calculate the electromagnetic shock, but we discussed the heat aspect with Yonder in the NA thread. Assuming a specific heat for the projectile and a speed will provide an impact temperature. Heat transfer equations would then define an expanding sphere of decreasing temperature, which, if you cut it to some "tolerable level" would sort of define the radius of the "hole" the projectile would melt in the ship.
Yes and no. The projectile is likely to turn into plasma on the whipple shield, which would reduce damage because the plasma would spread out before it hit the main armor. I think that the remaining momentum of the plasma and fragments would do the most damage, not heat transfer. Also, specific heat is not constant for a situation like this.
This said, I wonder whether the "turn into plasma over 30 km/s" rule applies in space. Air friction, and pressure, play a considerable role in heating fast moving objects. Would the same happen in space?
Francois
Absolutely. The plasma is not due to atmospheric heating. It's what happens when something is under pressure in the gigapascal-terapascal range that then gets released.
Well one can make some assumptions right? You [edit: i mean byron] say at high enough velocities our projectile turns to plasma, wouldnt that have a initial damage-profile compare-able to a very intense laserpulse due to the energy imparted on projectile and targed? Iirc some kind of Shockwave traveling through the matter or something?
Maybe. The problem is that the plasma is produced at the whipple shield, then expands to hit the hull itself. So it's less like a laser pulse, and more like a conventional explosion.
I haven't rally given much thought to the projectile shape. I assumed something like those fired by the US Navy Railgun, or a modern day APDS round
Steve
That would be a long rod. As an addendum, the projectile virtually has to be guided. If it doesn't hit straight on, then it loses most of its penetration.
-
Hi Byron
The projectile is likely to turn into plasma on the whipple shield, which would reduce damage because the plasma would spread out before it hit the main armor. I think that the remaining momentum of the plasma and fragments would do the most damage, not heat transfer. Also, specific heat is not constant for a situation like this.
How would the whipple shield work, then? I mean, for what I understand, modern day shields work for very light objects, with speeds in the tens of km per second. We're talking here of something weighing about a kilogram, colliding at a speed ranging from 100 to 1000 km/s.
At 100km/s, energy is 5 GJ, at 100, 500 GJ. Which means even if one percent of energy turns into heat, we get temperatures around a hundred of thousand kelvins, probably even millions for the faster projectiles... Wouldn't the whipple shield need to be very far from the ship to protect it from this kind of thermal shock?
I was asking that because it seems to me that over a certain energy, radiation output dominates (because its strength increases as a large power of the temperature, fourth if memory serves, and because it moves at lightspeed).
I might also be totally wrong (this wouldn't be the first time).
Francois
-
If I may cite research done by MIT in to a similar problem?
from http://www.mit.edu/people/daveg/Humor/ravioli_as_gas (http://www.mit.edu/people/daveg/Humor/ravioli_as_gas)
> There was still one aspect of the whole concept of a ravioli-loaded
> railgun type wepon which we, lolling about late on a weeknight, with
> only a few neurons randomly firing, could not resolve. Would a chunk
> of metal (can of ravioli) impacting another, larger, rest mass
> structure (star destroyer) produce an "explosion" effect, or simply
> punch an appropriately shaped hole as it passed through? Bill?
What am I, the neighborhood blast physicist??? Well, maybe... :-)
It all depends on speed of impact versus the speed of sound in the target
(what is called the Mach number, where Mach 1 means the speed of sound,
Mach 2 is twice the speed of sound, etc), and the speed of the ravioli
versus the speed of light in the target (which I'll call the Cerenkov
number, where Cerenkov 1 is the speed of light in anything; Cerenkov 1.3
is the speed of high-energy protons in a water-cooled reactor (that's why
you get that nifty blue glow), and you can get up to Cerenkov 2.4 using
diamonds and nuclear accellerators. In the late 40's people used to talk
about Cerenkov numbers, but they don't anymore. Pity.). Lastly, there's
the ravioli velocity expressed as a fraction of the speed of light in a
vacuum (that is, as a fraction of "c"). "C" velocities are always between
0 and 1.
At low speeds (REAL low) the ravioli will simply flow over the surface,
yielding a space-cruiser with a distinctly Italian paint job.
Faster (still well below speed-of-sound in the target) the metal of the
space-cruiser's skin will distort downward, making what we Boston drivers
call a "small dent".
Faster still, you may have a "big dent" or maybe even a "big dent with a
hole in the middle", caused by the ravioli having enough energy to push
the dent through, stretching and thinning the hull metal till the metal
finally tears in the middle of the dent.
Getting up past Mach 1 (say, 5000 feet/sec for steel), you start to get
punch-a-hole-shaped-like-the-object effects, because the metal is being
asked to move faster than the binding forces in the object can propagate
the "HEY! MOVE!" information. (After all, sound is just the binding
forces between atoms in a material moving the adjacent atoms -- and the
speed of sound is how fast the message to "move" can propagate.) From
this, we see that WileE Coyote often reached far-supersonic speeds because
he often punched silhouette-type holes in rocks, cliffs, trucks, etc.
Around Mach 4 or so, another phenomenon starts -- compressive heating.
This is where the leading edge of the ravioli actually starts being heated
by compression (remember PV=nRT, the ideal gas law?) Well, ravioli isn't
a gas, but under enough pressure, ravioli behaves as a gas. It is
compressed at the instant of impact and gets hot -- very hot. Likewise,
the impact point on the hull is compressed and gets hot. Both turn to
gasses -- real gasses, glowing-white-hot gasses. The gasses expand
spherically, causing crater-like effects, including a raised rim and a
basically parabolic shape. In the center of the crater, some material is
vaporized, then there's a melt zone, then a larger "bent" zone, and the
raised rim is caused because the gas expansion bubble center point (the
bending force) is actually *inside* the hull plate. If the hull plate
isn't thick enough, then the gas-expansion bubble pushes through to the
other side, and you get a structural breach event (technically speaking,
a "big hole") in the side of the space-cruiser.
Compressive heating really hits the stride up around 20,000 feet/sec (Mach
4 in steel, Mach 15 in air) and continues as a major factor all the way
up to the high fractional Cerenkov speeds, where nuclear forces begin to
take effect.
Aside: the "re-entry friction heating" that spacecraft endure when the
reenter the atmosphere is NOT friction. It's really compressive heating
of the air in the path. As long as the spacecraft is faster than Mach 1,
the air can't know to get out of the way, so it bunches up in front of
the spacecraft. When you squeeze any gas, it gets hot. So, the glowing
"reentry gas" is really just squeezed air, which heats the spacecraft heat
shield by conduction and infrared. The hypersonic ravioli can be expected
to behave similarly.
As we increase speed from the high Mach numbers (about 10 miles/sec) all
the way up to about 150,000 miles/sec, not much different happens except
that the amount of kinetic energy (which turns into compressive heat)
increases. This is a huge range of velocity, but it's uninteresting
velocity.
At high fractional Cerenkov speeds, the ravioli is now beginning to travel
at relativistic velocities. Among other things, this means that the
ravioli is aging more slowly than usual, and the ravioli can looks
compressed in the direction of travel. But that's really not important
right now.
As we pass Cerenkov 1.0 in the target, we get a new phenomenon -- Cerenkov
radiation. This is that distinctive blue glow seen around water-cooled
reactors. It's just (relatively) harmless light (harmless compared to
the other blast effects, that is). I mention it only because it's so
nifty...
At around .9 c (Cerenkov 1.1) , the ravioli starts to perceptibly weigh
more. It's just a relativistic mass increase -- all the additional weight
is actually energy, available to do compressive heating upon impact. The
extra weight is converted to heat energy according to the equation E=mc^2;
it looks like compressive heating but it's not.
[Here's where I'm a little hazy on the numbers; I'm at work and
don't have time to rederive the Lorentz transformations.]
At around .985 c (Cerenkov 1.2 or so), the ravioli now weighs twice what
it used to weigh. For a one pound can, that's two pounds... or about sixty
megatons of excess energy. All of it turns to heat on impact. Probably
very little is left of the space-cruiser.
At around .998 c, the impacting ravioli begins to behave less like ravioli
and more like an extremely intense radiation beam. Protons in the water
of the ravioli begin to successfully penetrate the nuclei of the hull
metal. Thermonuclear interactions, such as hydrogen fusion, may take
place in the tomato sauce.
At around .9998 c, the ravioli radiation beam is still wimpy as far as
nuclear accellerator energy is concerned, but because there is so much of
it, we can expect a truly powerful blast of mixed radiation coming out of
the impact site. Radiation, not mechanical blast, may become the largest
hazard to any surviving crew members.
At around .9999999 c, the ravioli radiation may begin to produce
"interesting" nuclear particles and events (heavy, short-lived particles).
At around .999999999999 c, the ravioli impact site may begin to resemble
conditions in the original "big bang"; equilibrium between matter and
energy; free pair production; antimatter and matter coexisting in
equilibrium with a very intense gamma-ray flux, etc.[1]
Past that, who knows? It may be possible to generate quantum black holes
given a sufficiently high velocity can of ravioli.
--Bill
[1]According to physicist W. Murray, we may also expect raining frogs,
plagues of locusts, cats and dogs living together, real Old Testament
destruction. You get the idea...
-
Very useful post. Damn, I'd like some ravioli right now.
Sadly not happening.
-
Very interesting, very informative, but still not a whole lot I can see as usefull for Newtonian Aurora.
A much simplified explanation: At hypervelocity speeds material strength becomes negligible, so only density, distance, and energy need be considered.
According to one approximate equation (http://www.alternatewars.com/BBOW/Ballistics/Shaped_Charge_HV_Penetration.htm) I found, penetration depth is proportional to the projectile length time the square root of the density ratios.
I'd hypothesize that a whipple shield functions by creating a composite 'material' of greater thickness at lower densities. So, spreading the same material across a greater thickness gives more protection per mass: very important in space.
As further hypothetical musings, lets consider Mr. Satellite with 3mm aluminum shielding, and 2mm Mr. Iron Splinter. Mr. Satellite and Mr. Iron meet at orbital velocity (say, 7,000 m/s.) 2mm * (7.86g/cm / 2.7g/cm)^.5 = 3.41 mm penetration. Since the impact energy, comparable to a .45 handgun round, hasn't vanished, the remaining energy might be modeled as a small 1 kJ explosion at that depth. This could be BAD since it is now on the wrong side of the shielding with vital circuitry.
However, if Mr. Satellite has 1mm aluminum shell plus 10 mm thick whipple shielding with 2mm equivalent thickness aluminum, then the penetration is 2mm * (7.86g/cm3 / 0.54g/cm3)^.5 = 7.86 mm. The resulting impact detonation now occurs inside the whipple shielding and outside the inner hull.
I'm sure real life whipple shielding is even more effective, but this might be simple enough to start building a Newtonian Aurora approximation.
Considering the 1kg 4800 MJ railgun: if it was an 8.9 g/cm3 copper sphere then it will be about 6cm in diameter, with an average thickness of 4cm any way it impacts.
The Emperial Ship Luckless has 5cm High Density Duranium Armor. According to the rules section, this absorbs 80MJ/cm and has 1g/cm3 density. The Railgun round has a maximum penetration of 4cm *(8.9/1)^.5 = 11.9 cm. Unfortunately, the luckless only has 5cm armor. The High Density Duranium absorbs 400 MJ. The remaining 4400 MJ expand into a plasma cloud gutting the ship. I'd propose modeling this by having the remaining dissipate like a conventional missile explosion against the opposite hull. Half the energy, 2200 MJ, exploding outwards to make an impressive exit wound. The other 2200 MJ exploding inward to make friends with the internal components.
Now lets say there are 'specialty armor' tech lines that can be optionally applied. Ablative armor to reduce laser and nuke thermal penetration (X effective multiplier against those, but damage depth is rounded up instead of down). Whipple Armor to reduce Kinetic Impact (lower density, greater thickness. same dmg rating). The Luckless_v2 might have (40% density, 5x thickness) whipple armor applied.
The same rail gun impact here penetrates 4cm *(8.9/0.4)^.5 = 18.9 cm. This penetrates 3 armor layers, and releases the remaining energy explosively between 3rd and 4th. (4800 - 3*80)/2 = 2280 MJ each direction. Looking at the Aurora Contact-Missile Explosion rules, 977 MJ seems to leak through the remaining two armor layers inward while the outbound energy goes to work widening the entry hole. Better, but still pretty bad. If the luckless had had 8 unit thicknesses of armor rather than 5 she might have survived with minimal casualties.
It isn't supper accurate, but given how little practical knowledge there is I think it might still be a place to start for Newtonian modeling.
-
Muzzle velocity of 4800 kJ railgun: 97km/s - 1kg projectile
Expected speeds (1/8 of delta v budget): Geosurvey Vessel - 3kkm/s
Expected closing speeds: 0.1kkm/s (firing up the engines) to 6.1kkm/s (head on collision)
Expected kinetic energy: 4.8GJ to 243GJ (note: quadratic scale, mid point is roughly 60.9GJ)
So we are looking at something around an order of magnitude higher energy than what you are assuming.
Making the projectile explode on impact will destroy any ship that isn't just a ball of armour.
Note that missiles set to ram will be many thousands of times heavier and move much much faster.
-
A 1kg 3k km/s has 4.5 TJ. With the mass disparity between a projectile and a ship, a 6.1k km/s head on collision is probably upwards of 18 TJ.
Anyway, the thread topic seems to be "What happens at 30 km/s+." I just thought mentioning 3,000 km/s+ effects might be overstepping and overkill.
So yes, a direct hit from two objects traveling head-on is probably death. Even with cookie cutter.
If cookie-cutter does happen, then at 3k km/s the previously mentioned copper sphere would punch 28.3 cm3 out of a single 1-cm layer of armor. By conservation of momentum, it would slow to 2,917 km/s releasing 125 GJ of energy in the process. I think this is where ravioli compression comes in. If this energy is transferred to the ship, the ship is probably doomed. If this is contained by the projectile, the ship is probably still doomed. Using constant 300K thermal heat capacity as an approximation seems to put the copper sphere at thermonuclear temperatures if it contains all 125 GJ.
At 2,917 km/s speed, the coper and compressed armor would have 17µs to expand while crossing a small 50m diameter ship. However, at 350 MK thermonuclear temperatures, radiative heat transfer dominates so completely that 17µs is plenty of time to cook the ship's interior. Simple lumped capacitance modeling shows GJs of radiative thermal energy transfer by the femtosecond. No, I don't believe that, but there is still going to be lots of hot death for cookie-cutter.
-
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.
-
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%.
-
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.
-
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
-
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.
-
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 symétric, 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
-
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)
-
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 symétric, 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.
-
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
-
Under no circumstances should railgun shots be 100% certain kills. It might be realistic, but it makes for lousy gameplay.
-
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.
-
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.
-
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
-
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
-
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.
-
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.
That's correct, I edited it in the post above...
Francois
-
As far as efficiency is concerned, a high rate of fire at close range will always beat a longer 'firing window'.
Hm, ok, that's a good point.
Muzzle velocity increases by sqrt of energy (which goes linear wrt size); minimum range decreases by ratio of muzzle velocity to ship speed
Hence 2x 200ton railguns will fire 2.5 times as fast as 1x 400ton railgun (2 guns with 0.8 cooldown).
Faster velocity of 400ton railgun marginally decreases inaccuracy, but certainly not by 60%. Since you will need to have seriously huge railguns before that translates to higher maximum range, I don't think ships would mount big guns, instead of lots of little ones.
Space stations might though. The cost of a big gun is mostly in the fuel needed to lug it around.
Also, wouldn't one-hit-one-kill make missiles mounting a railgun be seriously gamebreaking? Or if missiles can't mount weapons, then we might see the advent of the suicide fighter.
-
Armor: For near misses and lasers.
Currently things look like:
Rail Guns: Potential Instant kill if ship-accelerated for anything stationary that isn't protected by an atmosphere.
Defense: Don't be stationary if there is any chance of a rail gun armed enemy in sensor range.
Lasers: Not an instant kill. For hitting anything too mobile to get a Rail Gun lock on.
Defense: Armor and shields.
Nuclear Missile: For when you need to kill a maneuvering target from outside of laser range.
Defense: Active anti-missile systems.
Alternative Defense for of all: Kill them before they get close enough to kill you.
I'd say having an auto-jink setting may be essential to surviving combat without micromanaging. Lots of small random nudge maneuvers could probably be assumed to have in summation no net effect on ship course and thus neglected for position calculations while adding a miss-chance for non-guided rounds against an otherwise coasting target. If a rail gun refuses to fire for anything less than, say, a 1% hit chance, then no one would have to worry about Golden-BB events turning around key battles.
-
I think that one hit / one kill will probably be the name of the game in NA.
The real game won't be about surviving the hits. You just won't see that happen very often.
It will be about not getting hit.
Whoever can acheive the best hit % will be the winner. If there is one. MAD will be a real possibility in ship to ship battles in this game.
As I said, I plan on aiming to conduct my battles at ranges measured in AU. If I get close enough to be firing rail guns with a reasonable probability of hitting the enemy ship - they will likely be doing the same to me. The best I would hope for is to see that the other guy got destroyed before he kills me.
And on the issue of long rods for slugs, very possible - but I wouldn't bother unless it proved to be the only way you could launch a slug. Personnally I just want something that deposits the greatest percentage of energy on target. Penetration will likely be a moot point. The amount of energy the target will have to absorb should be enormous. If it was nothing but a shell around a mercury core (not feasable, just an example) that would 'splash' into a target - that would be fine. Conservation of energy will take care of the rest. The energy has to go somewhere and do something. A lot of 'something'....
-
I quite honestly think that directional defensive weaponry should be included for this reason.
Like outfitting Ships with Shrapnell tanks dropping a few thousand 5-20 gram metal pieces.
It will barely reduce laser power, not worth modeling at least, but it should fragment railgun projectiles and fore missiles to evade.
Directional shields a small distance from the ship might also be an option.
Basically everything you could think off based on the projected technology or todays to reduce the chance of a direct projectile hit.
-
I quite honestly think that directional defensive weaponry should be included for this reason.
Like outfitting Ships with Shrapnell tanks dropping a few thousand 5-20 gram metal pieces.
Your 'drop tanks' ought to be easy enough to model with a shrapnel warhead missile, depending on how Steve puts them together.
Just make one with a small / no engine, release, and have 'detonate'. Should produce a fair cloud of projectiles.
Then accel in a direction that will put the 'cloud' between you and incoming ordinance. If it is in a path that enemy ships would like to use - all the better.
I could even see dropping spreads of these missiles toward incoming vehicles. Harder to see than a ship with a rail gun and should create quite a bit of havoc if something blunders into them. I could also see them as 'escort missiles' used to accompany ship killing missiles and throwing out clouds of shrapnel to intercept incoming AMMs. Might be useful if nuclear 'escort missiles' are expensive.
-
And while railguns have some massive punch they are much slower then a laser thus would need more time to reach the targed if they arent fired on point blank range. I could see Smaller lasers and rails as point defence weapons if the targeting can be justified.
-
I'm not sure about point defenses against rail guns. Last time I tried plugging 1kg shells into the the Newtonian Sensor formula the detection range was something like 34 km for the sample Missile detection scanner. That's less than 0.5s reaction time against just a slow muzzle velocity only railgun round. Maybe single-use reactive explosive devices (reactive armor) could intercept an incoming round in time.
I'm worried about shipyards. Slow ship maneuvers can greatly limit effective railgun range, but if our massive unmoving shipyards are vulnerable to kinetic rains of death they could become dead yards walking as soon as any opposing railgun armed ship gets an active sensor ping. A reactive explosive device might protect against rare unlucky hits, but a lot of railgun rounds can get fired before a defensive missiles wave could close with the attackers.
-
Against the speeds projected, reactive armor doesn't work.
-
Against the speeds projected, reactive armor doesn't work.
My bad on the name. I meant something closer to plastering the hull with computer triggered claymore mines.
If hypervelocity Projectile + small obstruction = nuclear-like boom, then disrupting the incoming round 50m out would significantly reduce the damage.
If hypervelocity Projectile + small obstruction = very hot expanding plasma ball, then this wouldn't help much since most of the plasma would still hit the ship still at hypervelocity speeds.
EDIT: On further thought, while we may not know the exact rate of plasma expansion from such an intercept, we can calculate the maximum uniform expansion rate by converting the impact energy entirely into kinetic expansion rather than pure thermal. If a 1kg 1,000 km/s hyperveolocity round begins expanding into a spherical shell after striking 100g of oncoming shrapnel traveling at 10 km/s, then the combined mass ends up as a cloud traveling at 908.2 km/s toward the target while expanding at 290.4 km/s. If a 100m distant intercept was made, and the cloud is treated as a disk of uniform density, then the ship gets sandblasted with 0.32 g/m2 containing 128.2 MJ/m2 of impact energy. Actual dispersal rate would probably be lower and impact energy density higher.
The feasibility of 'operation short stop' depends on where a kinetic round would be detected and how fast a defense system could react.
-
Also, wouldn't one-hit-one-kill make missiles mounting a railgun be seriously gamebreaking? Or if missiles can't mount weapons, then we might see the advent of the suicide fighter.
Actually, I think an interesting weapon could be a "railgun toting ballistic drone" (RTBD). A projectile you'd send on a ballistic course towards a target, equipped with a passive sensor, which would close into range, and activate and shoot. Such a small object, on a ballistic course, would be extremely hard to detect, but very deadly once it activates (if it can close in).
Thinking of it, it might mean that the old "non newtonian" idea of ships expending fuel for distance travelled and not acceleration might not be as irrealistic as we'd have thought. Against such railgun drones, the best strategy for a ship under threat would be make small course changes at all times, and this would use fuel on a "per distance" basis...
Francois
-
My vision of railgun drones (because missiles with weapons may as well be called drones) involves them accelerating all the way to the target.
(depending on how the damages work out, they might not have to do this. Burn 50% of delta-v then reserve for course correction might be more than enough)
Drones can pack much higher fuel to mass ratio since they are one-shot (and can burn all their delta-v) which means the closing speed of the drone will be obscene, the drone can then fire its railgun shells at all targets and then attempt to ram something.
If the drone itself hits, that thing is gone. Armour, fancy shields, uber big moon-sized battlestation, all gone. Nothing will survive a 5ton object hitting it at 60kkm/s. Maybe not even planets (the planet itself will live, not sure about anything on it)
And at 60kkm/s relative speed, any hit from railguns will also likely blow away vast amounts of opposition.
...
You know, when this all comes out, I'm totally going to make fighters. No carriers, just really really small ships. Single weapon or missile launcher, that's it. Jumpships and support (like radar and coillers) will probably be bigger, but I don't intend to put those on the line of battle.
When every shot is lethal, you want your enemy's shots to overkill as much as possible. Why build big battleships when they die to one shot anyway? Better to have many tiny ships and eat the inefficiencies. They'll pay you back when the lucky 30% of your stuff comes back, instead of 1 lonely ship that lived through a mid-range nuke.
-
With regard to the cloud of 1000 kilogram objects. Something like that will be in the game, initially as a missile warhead but I am sure that will be adapted to a variety of uses, both offensive and defensive.
Every time I think "OMG these weapons are going to be too powerful", I remind myself that this is reasonably realistic physics and that future combat spacecraft will have to deal with these type of weapons. I am sure tactics will evolve to deal with the situation. I just don't know what they will be :). As several posters have mentioned, spacecraft speed is often going to be more important in terms of damage than railgun launch speed, although railgun launch speed may be more important in terms of controlling the engagement and the ability to set up a potential intercept shot. Personally, I think I would probably move as slowly as tactically feasible if I am likely to encounter hostile railgun fire.
Steve
-
Personally, I think I would probably move as slowly as tactically feasible if I am likely to encounter hostile railgun fire.
Or play chicken with your enemy by suicide running your ships into his. And hoping yours are cheaper.
Who says fighters aren't feasible? They're *totally* feasible and even cost efficient!
Would like a railgun drone though. (weight penalty for automated systems?)
-
Or play chicken with your enemy by suicide running your ships into his. And hoping yours are cheaper.
Who says fighters aren't feasible? They're *totally* feasible and even cost efficient!
That's called a missile.
With regard to the cloud of 1000 kilogram objects. Something like that will be in the game, initially as a missile warhead but I am sure that will be adapted to a variety of uses, both offensive and defensive.
Every time I think "OMG these weapons are going to be too powerful", I remind myself that this is reasonably realistic physics and that future combat spacecraft will have to deal with these type of weapons. I am sure tactics will evolve to deal with the situation. I just don't know what they will be :). As several posters have mentioned, spacecraft speed is often going to be more important in terms of damage than railgun launch speed, although railgun launch speed may be more important in terms of controlling the engagement and the ability to set up a potential intercept shot. Personally, I think I would probably move as slowly as tactically feasible if I am likely to encounter hostile railgun fire.
Steve
I would like to point out that, while the physics are entirely realistic (and bravo for that, Steve) the engineering is way out there. Massive kinetic kill is a fact of life at the sort of velocities we expect here. The scenario is more balanced at lower velocities.
-
Yeah, but that would require a very limited in-system hyper jump.
Which is why I suggested it in the first place, though I got convinced it's not in the spirit of realism.
I suppose all this construct relies on super-efficient fuel.
-
Yeah, but that would require a very limited in-system hyper jump.
Which is why I suggested it in the first place, though I got convinced it's not in the spirit of realism.
I suppose all this construct relies on super-efficient fuel.
No, it would just slow the game's pace even more. I'm pointing out that the massive kinetic overkill is a natural consequence of Steve's design decisions.
-
That's called a missile.
Missiles don't shoot railgun shells. Although fragmentation missiles might do the job just as well. Railguns might have enough of a velocity boost to increase firing solutions significantly though.
Maybe it might be time to design those *really* huge missiles. 2-stage 50ton missile, fuel efficiency on first stage for long boosting times and massive delta-v.
With a powered flight range of pluto orbit, payload of a couple of thousand shells, max delta-v of "you're dead".
-
Missiles don't shoot railgun shells. Although fragmentation missiles might do the job just as well. Railguns might have enough of a velocity boost to increase firing solutions significantly though.
Maybe it might be time to design those *really* huge missiles. 2-stage 50ton missile, fuel efficiency on first stage for long boosting times and massive delta-v.
With a powered flight range of pluto orbit, payload of a couple of thousand shells, max delta-v of "you're dead".
It was the "suicide fighter" idea I was talking about. Though I'm all in favor of drones.
-
It was the "suicide fighter" idea I was talking about. Though I'm all in favor of drones.
Well, depending on how the game engine goes, might need to make suicide fighters after all.
Drones might not be able to mount railguns (where's the firecontrol going to go?). And if they could, might not be able to change targets. And perhaps not operate in squadrons for remote active sensors. (this bit is actually the bit I think is most likely to be possible)
Might need to rely on suicide fighters. But the principle is the same.
-
So, it comes down to automation so you can build that 200 ton fighter without any crew at some point^^
-
So, it comes down to automation so you can build that 200 ton fighter without any crew at some point^^
Huh? Why would you need automation?
It's a suicide fighter, yeah? =D
-
Speaking of impact physics, conventional missiles ought to replace the warhead with concrete and become guided kinetic kill vehicles.
The 5ton sample conventional missile does a little over 10GJ on contact, and must make contact to do damage.
However, 3.5 tons moving at 1200 km/s (missile mass minus fuel mass at roughly 50% max deltaV) would contain 2,520,000 GJ of energy. The actual warhead seems a little frivolous.
No wait, here's a better idea: build a 10 ton anti-ship kinetic kill vehicle that has a nuclear 2.5 ton anti-anti-missile where the old warhead once was. :D
-
Well, depending on how the game engine goes, might need to make suicide fighters after all.
Drones might not be able to mount railguns (where's the firecontrol going to go?). And if they could, might not be able to change targets. And perhaps not operate in squadrons for remote active sensors. (this bit is actually the bit I think is most likely to be possible)
Might need to rely on suicide fighters. But the principle is the same.
So it's a kamikaze railgun fighter. Earlier, you said something about a suicide fighter, which I interpreted as a "ram the target" thing. Which would make it a missile.
-
So it's a kamikaze railgun fighter.
Yes, that. The railgun is engineered to be the biggest thing you could fit on the fighter, to improve the possible firing solutions.
I called it the suicide fighter because it probably won't survive contact and it won't have enough fuel to slow down. Given that the proposed use was for it to be based on carriers and intercept targets appearing at hyperlimits, odds are that the fighters will go sailing out of the system after the attack run is done.
Whether it does so as an intact fighter or a rapidly expanding cloud of plasma depends on whether the enemy is pissed at having died.
The concept itself might need some fine-tuning. Instead of building a big railgun, it might be easier to simply mount small railguns and have a few smaller fighters. Depends on how small you can them (and thus how much mass you waste on crew life support etc.)
-
I called it the suicide fighter because it probably won't survive contact and it won't have enough fuel to slow down. Given that the proposed use was for it to be based on carriers and intercept targets appearing at hyperlimits, odds are that the fighters will go sailing out of the system after the attack run is done.
Whether it does so as an intact fighter or a rapidly expanding cloud of plasma depends on whether the enemy is pissed at having died.
The concept itself might need some fine-tuning. Instead of building a big railgun, it might be easier to simply mount small railguns and have a few smaller fighters. Depends on how small you can them (and thus how much mass you waste on crew life support etc.)
This is pretty much what I have been looking at for system defense. I think I will try the smaller railgun and try to pack in as many as I can to maximize 'target saturation'. Unless the speeds are reduced, a small railgun hitting like a nuke will be just as good as a big one hitting like a larger nuke.
Ships that go from system to system won't be able to use this design, but as a system defense unit I believe it will be hard to beat.
-
Unless the speeds are reduced, a small railgun hitting like a nuke will be just as good as a big one hitting like a larger nuke.
I'm not getting a big railgun for the larger damage. In fact, smaller railguns will allow for smaller fighters or more delta-v, hence smaller railguns will actually hit harder. (sorium fuel is more energy dense per ton than railgun power)
The big railgun is for a bigger window of 'intercept' where you have firing solutions. If you make "iron bombers" with a 1ton railgun, your window of firing solutions might be <1s...
Your enemy will be trying to maneuver out of your way, and going at insane speeds means you might have a problem trying to turn fast enough.
-
As far as railgun defense goes, has anyone looked at the possibilities for shields? Based on the stats Steve has provided us (and I don't recall if he gave us shield stats) would it be possible to design a shield that can stop railgun impacts?
-
Yes, by having it about one ship length away from the hull (given sufficiently big ships), and able to withstand at least the base energy of the railgun.
The shot would dissipate, letting only a small part hit the ship, which gets a chance to absorb it with it's armor.
Still requires a think belt, and it'll owrk only once, while increasing the chance of being hit significantly.
I wonder if that's a good prospect.
-
Besides impacting on hull, have we talked about impacting on planets?
For a small 1kg ball of generic metal, 1000km/s relative is 0.5TJ, which I would expect to generate a nuke-like explosion in the upper atmosphere.
But as the speeds increase and the chunk gets heavier (mass driver is 1kg, fragment missile might be 1-10kg, kinetic strike missile could be 10tons), you could get some obscene energies, and then what happens?
10 tons (15tons full load) at 10 000 km/s relative (say a missile burning all delta-v, tech based off geosurvey vessel) is 500PJ. Even if it turns into plasma in the upper atmosphere, that's alot of air heading downwards very fast.
Besides, a long-range anti-planet missile could be fine-tuned for maximum energy yield with a really long burn time (high efficiency engines).
-
Obscene energies just make either a bigger explosion or a longer 'explosion.'
500PJ is, what, a 200 mega-ton explosion?
A direct impact with a small rocky body like an asteroid would possibly end with lots of smaller asteroids.
A direct impact on Earth would be mostly just spectacular when the missile disintegrates into a fireball over 60km up. At that distance up into the mesosphere I would't expect much physical damage to the planet or infrastructure, although some might get blinded if they were looking in the wrong direction at the wrong time.
Earth's atmosphere acts like a really really good Whipple Shield.
I tried entering the problem into an online asteroid-impact simulators, but they all rejected anything moving at that speed. So I tried again, using a 198,000 ton asteroid moving at 71 km/s with "Impact: Earth!". The greater momentum and ablative mass allowed the projectile to close to 7.4 km above the surface before loosing integrity and disintegrating into a 115 mega-ton air-burst, with small chunks raining down to the surface without leaving any creater. According to the report, the air-burst would produce a 74 dB of noise at a spot 100 km away on the ground.
Any planet with a decent atmosphere probably doesn't have to worry. Your mining colonies might need to worry.
-
I think we calculated all that about 20 pages back.
General consensus was that it would probably damage the ecosphere, but not be a direct thread to anything living on the surface.
Nukes will be noticeably more effective.
-
yeah invasion works the best once everything else is dealt with
-
How about mid-range tech and a larger planet-buster missile?
20 tons (40tons full load) with 60kkm/s relative? That's... 36 000 PJ. Or 14.4 gigaton explosion. (@200 mtons to 500PJ)
Tangent: what's after P again? =P
http://impact.ese.ic.ac.uk/cgi-bin/crater.cgi?dist=1&diam=0.8419&pdens=8000&pdens_select=0&vel=60000&theta=90&tdens=1000&tdens_select=0
Doesn't do very much apparently.
Needs to go up to 200kkm/s for a 20ton iron ball to break windows 1km away from impact site.
-
I have very, very serious doubts about the accuracy of that calculator at 200,000 km/s (or .67c). It's designed for asteroids at dozens of km/s, so take any numbers with a couple kilograms of salt.
-
Most of what is discussed here goes right over my head, i have to admit.
Something my common sense (allways dangerous to use in this kind of threats :) ) tells me is, that it highly doubts the projectile even has _time_ to breake up. It hits the atmorphere at 60.000 km/s, not the 30ish km/s of your regular asteroid. How does the atmosphere interact with that, would the missile have time to even react in any way or would it be through the atmosphere before any effect can take effect?
Or would the atmosphere be like a brick-wall, turning the missile into a ball of plasma? And then what? Whould the plasma be stoped dead in it´s track (I doubt that) or hit the ground at a somwhat slower, but still very significant speed?
Just a few things I am wondering, perhaps more knowledgable people can enlighten me ;)
-
Most of what is discussed here goes right over my head, i have to admit.
Something my common sense (allways dangerous to use in this kind of threats :) ) tells me is, that it highly doubts the projectile even has _time_ to breake up. It hits the atmorphere at 60.000 km/s, not the 30ish km/s of your regular asteroid. How does the atmosphere interact with that, would the missile have time to even react in any way or would it be through the atmosphere before any effect can take effect?
Or would the atmosphere be like a brick-wall, turning the missile into a ball of plasma? And then what? Whould the plasma be stoped dead in it´s track (I doubt that) or hit the ground at a somwhat slower, but still very significant speed?
Just a few things I am wondering, perhaps more knowledgable people can enlighten me ;)
I'm gonna go with brick wall. A simple dynamic pressure calculation says that at 50 km altitude and 60,000 km/s, a projectile will experience a pressure of 1.95 TPa (TeraPascals) or 2.83e11 Psi. That's way, way above the strength of any material I know, and the density (which dynamic pressure is proportional to) is only .00108 kg/m3, as opposed to 1.225 at sea level. So the object will suffer mechanical failure in the high atmosphere. At the same time, 1.95 TPa will also slow down the projectile. If it has a sectional density of 10,000 kg/m2, the resulting acceleration will be 1.95e8 m/s2. That's a very, very large number, and that means a lot of heat will be produced.
If it takes the projectile .001667 seconds to traverse the atmosphere, and over that time the above acceleration is constant (both of which are wrong, but I'm trying to get a handle on how much heat is generated), then over that time, the projectile will decelerate by 325 km/s. For each kilogram of projectile, that amounts to 19.4 terajoules of heat generated. That's more then enough to flash-vaporize the whole thing, even if 90% goes into the atmosphere, no matter what it's made of.
I know that TransNewtonian materials might change the values, but to survive, an object would have to be orders of magnitude more durable then anything we can make today.
As for what the resulting plasma would do, I'm under the impression that it would rapidly expand, reducing sectional density and slowing down faster and faster, so that it stops in the upper atmosphere. The big problem would not be the projectile's momentum, but the energy it carries. I'm not saying that any of this would be pleasant to be around, but it's going to behave more like a high-altitude bomb then a physical projectile.
-
I have very, very serious doubts about the accuracy of that calculator at 200,000 km/s (or .67c). It's designed for asteroids at dozens of km/s, so take any numbers with a couple kilograms of salt.
Of course most of that would be way off, but it at least has some justification.
Also, played around with the numbers on the calculator a bit and it needs around a 37 meter radius iron ball to reach the ground at 60kkm/s. Aka. you need to slam a destroyer sized missile to do any real damage. (75km radius fireball is pretty nice)
http://impact.ese.ic.ac.uk/cgi-bin/crater.cgi?dist=75&diam=37&pdens=8000&pdens_select=0&vel=60000&theta=90&tdens=1000&tdens_select=0
Although a destroyer would have rather lower density and so would need to be *even* bigger.
-
Of course most of that would be way off, but it at least has some justification.
Also, played around with the numbers on the calculator a bit and it needs around a 37 meter radius iron ball to reach the ground at 60kkm/s. Aka. you need to slam a destroyer sized missile to do any real damage. (75km radius fireball is pretty nice)
http://impact.ese.ic.ac.uk/cgi-bin/crater.cgi?dist=75&diam=37&pdens=8000&pdens_select=0&vel=60000&theta=90&tdens=1000&tdens_select=0
Although a destroyer would have rather lower density and so would need to be *even* bigger.
No, it would not reach the ground at all. As noted previously, it would disintegrate in the upper atmosphere, and, though my knowledge of material failure is far from complete, I believe it would probably become a fairly fine powder, slowing down rapidly, and dumping a lot of heat into the atmosphere. Think really big nuke. I'm not saying it would be pleasant, but no body of reasonable size will be able to survive such treatment. Note that I say reasonable size. If you slammed something like the moon into Earth at 60 Mm/s, then yes, it probably would reach the ground more or less intact.
-
Which was why I was slowly increasing the
radius diameter of that iron ball until it did reach the ground in the calculator. If you just increase the size, at *some* point, something will be left to reach the ground.
You might also note that according to the calculator, the bits left are traveling only just over 1/3 of their original speed and have spread out into a circle 0.256km in diameter. And isn't a complete chunk anymore. Perhaps the only thing reaching the ground would be the 75km wide fireball...
So, in *your* opinion, approximately how big would the ball need to be for something to reach the ground? Maybe a battleship (say 100meters?) would reach the ground? =P
Perhaps we could model it as a increasingly dense particle beam travelling at 60kkm/s ablating the surface of the ball of iron.
Obviously, their assumptions about how the projectile breaks up needs to be looked at rather closely to see if they become significantly inaccurate at high speeds. And I suspect they would be since this calculator is made for asteroid impacts...
EDIT: you might also note that the calculator says the projectile breaks up at 145km from the ground.
----------------
As a side note: it would be really cool to watch such an impact. From a safe distance of course, like from orbit. 100 meter wide ship slamming into a planet isn't going to be very healthy from inside the atmosphere...
EDIT2:
Screw practicality. Like the "boost ship to lightspeed" megaproject, I think I will add in an optional component: "point at planet with atmosphere for hugely-impractical relativistic iron bomb"
-
Which was why I was slowly increasing the radius diameter of that iron ball until it did reach the ground in the calculator. If you just increase the size, at *some* point, something will be left to reach the ground.
You might also note that according to the calculator, the bits left are traveling only just over 1/3 of their original speed and have spread out into a circle 0.256km in diameter. And isn't a complete chunk anymore. Perhaps the only thing reaching the ground would be the 75km wide fireball...
So, in *your* opinion, approximately how big would the ball need to be for something to reach the ground? Maybe a battleship (say 100meters?) would reach the ground? =P
Perhaps we could model it as a increasingly dense particle beam travelling at 60kkm/s ablating the surface of the ball of iron.
I don't think it would happen in any meaningful way for any object that is of non-astronomical size. First, the calculator does not take into account entry heating on the object. Normally not a big deal, but when you get to these sort of velocities, slowing down any releases enough heat to turn everything in the area into plasma. Second, the fragments in question will be pulverized. At terapascals of pressure, tenths of a percent variations in pressure will cause failures. That makes them very small, which means they lose energy more quickly. Which in turn causes the heating mentioned earlier. The object quite literally will turn into plasma, which makes the question of "reaching the ground" moot. By the calculator's model, the chunks that reach the ground are under dynamic pressures on the order of 20 TPa. I really doubt that they'd survive to get to that point.
Obviously, their assumptions about how the projectile breaks up needs to be looked at rather closely to see if they become significantly inaccurate at high speeds. And I suspect they would be since this calculator is made for asteroid impacts...
EDIT: you might also note that the calculator says the projectile breaks up at 145km from the ground.
There are varying degrees of "high speed". You could say that high speed is what you do on the highway (100 km/hr) or what an airliner does (1000 km/hr). Neither is terribly relevant to supersonic flight, which can be over 1 km/s. In much the same way, a model that is good for things at 5-60 km/s is unlikely to be good for things at 60,000 km/s. The failure height makes sense. I would like to point out, though, that it is disintegrating at an altitude 50% greater then the technical definition of 'space'. I used 50 km because it was a nice round number and my tables didn't go much higher.
Another thing is that we have absolutely no experience dealing with objects in this velocity range. At all.
I read through some of the documentation (http://www.purdue.edu/impactearth/Content/pdf/Documentation.pdf) and it is definitely not intended for impacts in the range we're using it for. In fact, the newer version (http://www.purdue.edu/impactearth) doesn't go beyond 72 km/s, which makes me suspect that the authors consider it to be inaccurate above that velocity.
The program saying that it reached the ground intact is an artifact of the way the program handles breakup. It says airburst when the projectile reaches 7 times original diameter. You kept increasing diameter until it just stopped telling you that (particularly as it told me 36m airburst at 225m), when actually, it would have broken up when it was probably twice original diameter.
-
Heating of the entry to atmosphere could be calculated by if they wanted to resistance and burning up. What about some form of heat shielding on missiles at advanced technologies with advanced ECM being added to.
The other option is the ability to attach engines to asteroids and ramming them at planets. Could be another addition to game and has been proposed as future weapons technology
-
Heating of the entry to atmosphere could be calculated by if they wanted to resistance and burning up. What about some form of heat shielding on missiles at advanced technologies with advanced ECM being added to.
The other option is the ability to attach engines to asteroids and ramming them at planets. Could be another addition to game and has been proposed as future weapons technology
It's not that difficult to calculate. Almost all of the lost kinetic energy goes into heat.
And good luck finding a heat shield that will take those kinds of stress. Or those kinds of heat.
If you're going to destroy a planet, just nuke it. It's easier and cheaper.
-
If you're going to destroy a planet, just nuke it. It's easier and cheaper.
I'm not sure about that. Sorium is more abundant than anything else now (eg. Tritium for warheads) and mines faster than anything else.
And fuel is ridiculously energy dense; which can be packed into a high speed projectile by a high speed ship shooting a high delta-v missile, all without increasing the missile's weight.
Even if the missile turns into plasma in the upper atmosphere (I think you mentioned 50km?), the resulting nuclear fireball could be big enough to reach the ground.
I mean, by middle of the tech levels, missiles in high speed runs would be thrown from opposite the system and have relative velocities up to ~100 kkm/s. 20 ton missile at 60kkm/s relative is 200 megatons, scaling by square of speed (which is roughly linear wrt. fuel efficiency?).
I don't think you could stuff a nuke warhead into a 20ton missile that would match that yield at the same tech level and fuel is certainly cheaper than warheads. Sure, nukes would be a ground level detonation and you need it to hit something important, but both have terminal guidance. (high speed missile is also harder to block due to less reaction time)
At the very least, sorium warheads, if possible, would beat anything else for cost.
-
I would agree with byron that a relatively slow missile that can transit the atmsphere is going to be more effective that one that is basically trying to shove it out the way.
I'm now wondering if the best planetary defense would actually just be a bunch of terraformers that busily pumped up the atmosphere density to the maximum tolerances of my inhabitants.
-
At high velocities the atmosphere is largely treated as a solid. In reality compression would occur that would make a material with the number of atoms of the column of air equal to the missiles diameter. Essentially once the missile's transit time through the atmosphere is shorter than the ability of the air to move away from it the air is simply compressed. Pretty much as happens with a piston. The temperature rise is such the molecules disassociate into atoms. This heat is conducted into the missile body but again due to the short time involved...(at 0.1c 50 km requires 1.7 ms) only the upper fraction of the missile would convert into plasma but the plasma would have the same mass, and momentum (hence kinetic energy) of the original missile. The energy required to compress that air column would be lost to the missile but I suspect that it is not enough to slow the missile down significantly.
When the missile strikes the ground the entire mass of the missile (plus the air column) is then converted into kinetic energy and dispersed via the shock wave and in large part transferred to all the debris thrown up. In principle though everything within a reasonable distance of the missile strike would be converted into plasma by the energy contained in the missile and only once the fireball expanded and cooled would you start seeing debris thrown upwards.
Note the ground shock wave would be extremely powerful. But even the air shock would be considerable...the missile impact probably is causing an outward going pressure shock front that would meet the inbound atmosphere from the vacuum left by its passage with ugly results.
There is no need for warheads on missiles that can achieve even low fractional C velocities.
The plasma is no less dangerous then a metal bar. It is fully capable of transmitting shock and energy to a material. HEAP rounds convert a titanium cone to a directed plasma jet to slice through armour, and plasma cutting is a standard way to cut thick metal. Any oxyacetylene torch is a plasma as well.
A plasma strike is what does damage in a nuclear blast in space. It is the warhead/missile being converted into plasma that is doing the damage as there is no atmosphere to transmit the energy. All the other energy is contained in particles and photons...which are not negligible but follow a r2 law so they loss energy rapidly with range.
An impact of a 20 tonne object moving at speeds were relativistic corrections become important (v>>0.75c) would be very nasty. Luckily most planets are massive enough (earth is 6x10^24 kg) that outright destruction is hard to produce...but for environment I'd say that is a different situation. You would need to accumulate a total mass of 10^7 kg of material in the missile plasma before the velocity of the plasma would drop from 10^8 m/s to 10 m/s or so. Not completely accurate but assuming the plasma remains around 4 m in diameter that only takes 150 m for a planet of the density of the earth 5.5tonne per m3...so the missile impact depth is around 150 m, in water it would be something like 1 km. At this point the plasma is roughly stationary and transfers its energy to the surroundings...which promptly sublimate and then the shockwaves from that spread.
-
I'm not sure about that. Sorium is more abundant than anything else now (eg. Tritium for warheads) and mines faster than anything else.
And fuel is ridiculously energy dense; which can be packed into a high speed projectile by a high speed ship shooting a high delta-v missile, all without increasing the missile's weight.
Even if the missile turns into plasma in the upper atmosphere (I think you mentioned 50km?), the resulting nuclear fireball could be big enough to reach the ground.
I don't disagree with this. I was commenting on a proposal to allow the use of asteroids as weapons. And for that, you tend to go for mass over velocity. And it would break up well above 50 km. I just chose to find dynamic pressure there.
I would agree with byron that a relatively slow missile that can transit the atmsphere is going to be more effective that one that is basically trying to shove it out the way.
I'm now wondering if the best planetary defense would actually just be a bunch of terraformers that busily pumped up the atmosphere density to the maximum tolerances of my inhabitants.
Not a bad idea. However, it really wouldn't do much to mitigate the damage. All this does is make it impossible to physically hit ground-level targets.
At high velocities the atmosphere is largely treated as a solid. In reality compression would occur that would make a material with the number of atoms of the column of air equal to the missiles diameter. Essentially once the missile's transit time through the atmosphere is shorter than the ability of the air to move away from it the air is simply compressed. Pretty much as happens with a piston. The temperature rise is such the molecules disassociate into atoms. This heat is conducted into the missile body but again due to the short time involved...(at 0.1c 50 km requires 1.7 ms) only the upper fraction of the missile would convert into plasma but the plasma would have the same mass, and momentum (hence kinetic energy) of the original missile. The energy required to compress that air column would be lost to the missile but I suspect that it is not enough to slow the missile down significantly.
When the missile strikes the ground the entire mass of the missile (plus the air column) is then converted into kinetic energy and dispersed via the shock wave and in large part transferred to all the debris thrown up. In principle though everything within a reasonable distance of the missile strike would be converted into plasma by the energy contained in the missile and only once the fireball expanded and cooled would you start seeing debris thrown upwards.
Note the ground shock wave would be extremely powerful. But even the air shock would be considerable...the missile impact probably is causing an outward going pressure shock front that would meet the inbound atmosphere from the vacuum left by its passage with ugly results.
There is no need for warheads on missiles that can achieve even low fractional C velocities.
Really? The projectile will begin heating and suffering aerodynamic stresses somewhere above 150 km, which is three times what you estimated. Also, what's stopping it from breaking up under the load? Just curious.
The plasma is no less dangerous then a metal bar. It is fully capable of transmitting shock and energy to a material. HEAP rounds convert a titanium cone to a directed plasma jet to slice through armour, and plasma cutting is a standard way to cut thick metal. Any oxyacetylene torch is a plasma as well.
No, that's not how HEAT rounds work. The copper liner stays in metallic form the entire time, but behaves like a liquid under the pressure. And neither an oxyacetylene torch cuts by heating the metal, not by momentum transfer. So does a plasma torch for that matter.
A plasma strike is what does damage in a nuclear blast in space. It is the warhead/missile being converted into plasma that is doing the damage as there is no atmosphere to transmit the energy. All the other energy is contained in particles and photons...which are not negligible but follow a r2 law so they loss energy rapidly with range.
No, that's not what does the damage. The damage is done by the X-rays from the bomb itself. The casing is fairly negligible.
-
I don't disagree with this. I was commenting on a proposal to allow the use of asteroids as weapons. And for that, you tend to go for mass over velocity. And it would break up well above 50 km. I just chose to find dynamic pressure there.
I looked up hypervelocity weapons on that atomic rockets site. They calculate that the ideal energy point of an accelerating missile is when it's speed is equal to exhaust velocity. Beyond that, burning more fuel reduces KE since your fuel's mass is worth more energy.
Given that I calculated the exhaust velocity of the Geosurvey vessel as 19100 km/s, that would mean that kinetic missiles will be travelling at 19kkm/s... at starting tech.
Naive conservation of momentum indicates to me that your missile will need to be 50% fuel to achieve this.
EDIT: for obvious reasons, your ships launching missiles should have their own velocity and hence some buffer should be added. Say 55% fuel and 45% engine. The missile would accelerate to exhaust velocity and then start evasive course changes using the extra 5%.
-
Given that I calculated the exhaust velocity of the Geosurvey vessel as 19100 km/s, that would mean that kinetic missiles will be travelling at 19kkm/s... at starting tech.
That assumes that the engine has the same exhaust velocity. I know that's obvious, but I for one expect the missile to have a considerably lower exhaust velocity. Particularly early in the game, I'm not going to build missiles to kill planets.
Naive conservation of momentum indicates to me that your missile will need to be 50% fuel to achieve this.
Naive indeed. No offense. And you really should read all of atomic rockets. It's a great site. And now for some rocket science:
For delta-V to equal exhaust velocity, the mass ratio is actually going to be about 2.7. The mass ratio is defined as the ratio of loaded mass to empty mass. Delta-V is calculated from the rocket equation: DV=Ve*ln(Ml/Me) DV is delta-V, Ve is exhaust velocity, ln is the natural log, and Ml and Me are the loaded and empty masses respectively. Note that loaded and empty only refer to the fuel tanks. Anything else is factored into both.
-
Hm, 2.7 doesn't sound all that much. Certainly affordable at least.
Still, 20kkm/s does not make a planet-killer. It makes a very good ship killer though (although for AS work, you'd probably want more smaller missiles at a lower velocity)
-
an interesting strategic element for terraformers against fast moving missiles burn em up versus having them hit. Sorium perhaps could be needed if u wanted a guided missile.
And the affordable factor versus perhaps a higher manufacture cost and was to intercept them as well. From an impact physics point of view something to consider, steve seems to have been offline for a week waiting to see what he thinks of some of these new ideas whenever he graces his presense again
-
At high velocities the atmosphere is largely treated as a solid. In reality compression would occur that would make a material with the number of atoms of the column of air equal to the missiles diameter.
I think most folks are looking at this backward. This missile won't reach the ground intact. It is easier to look at it in reverse.
Instead of wondering if the missile will punch through that much air and reach the ground at this velocity, try to imagine hitting the missile with this amount of particles at this velocity and it surviving. It won't.
The atmosphere is going to act like a solid. A diffuse one, but a solid. One that when slammed into the missile will disintegrate it. Big high altitude air burst. If it will reach the ground is totally a function of its energy. A lot of it is going to be reflected into the upper atmosphere again as it rebounds off of the tropopause, etc in the different layers of the atmosphere, just like sonar echos off the thermocline.
-
I think most folks are looking at this backward. This missile won't reach the ground intact. It is easier to look at it in reverse.
Instead of wondering if the missile will punch through that much air and reach the ground at this velocity, try to imagine hitting the missile with this amount of particles at this velocity and it surviving. It won't.
The atmosphere is going to act like a solid. A diffuse one, but a solid. One that when slammed into the missile will disintegrate it. Big high altitude air burst. If it will reach the ground is totally a function of its energy. A lot of it is going to be reflected into the upper atmosphere again as it rebounds off of the tropopause, etc in the different layers of the atmosphere, just like sonar echos off the thermocline.
The first part is entirely correct, but I'm not so sure about the last part of your statement. Momentum in this situation is almost negligible. Once the projectile breaks up, the sectional density goes way down, dumping energy/momentum even faster. Almost all movement in this case is going to come from the heated air, which will be moving in all directions. I don't see it "rebounding" at all.
And I'm even more skeptical of the person you quoted, given that he got just about everything else completely wrong.
-
The question of course is whether your missile going at c-fractional speeds (coz 60kkm/s is 20% of c) will generate an airburst large enough for that to affect the ground.
Given the kind of energies we are throwing around at even early-mid game, I'd say the shockwave alone should do plenty of damage on the ground under the atmosphere entry site. It certainly won't destroy all the biosphere, but you didn't want to do that anyway.
-
The question of course is whether your missile going at c-fractional speeds (coz 60kkm/s is 20% of c) will generate an airburst large enough for that to affect the ground.
Given the kind of energies we are throwing around at even early-mid game, I'd say the shockwave alone should do plenty of damage on the ground under the atmosphere entry site. It certainly won't destroy all the biosphere, but you didn't want to do that anyway.
The answer depends heavily on the size of the projectile. Even at .999c, 1 gram isn't going to do more then maybe make a flash when viewed from ground level (454 kilotons). A few kilograms might make me nervous, except that the burst altitude is probably over 100 km, which makes it somewhat less of a threat. Once past that, it gets very dangerous, very fast.
The airburst will form a shockwave. Nuclear weapons produce shockwaves because they heat the air around them to incredibly high temperatures. The same thing happens here.
-
We probably won't get 99.9% c.
I have seriously doubts about the practicality of acheving 90+% c anyway. 100kkm/s ought to be enough to kill anything you hit.
EDIT: I reserve the right to build yatches that go that fast at end-game. Simply for the lulz. =)
A 5ton missile at 100kkm/s could doable by midgame (Steve said that late game fuel efficiency was just under c?). That's... what, 25E18 J? Or about 6 gigatons?
Even with an additional 5-10% fuel weight for maneuvering and spreading out attack vectors to avoid interception, the missile shouldn't reach much more than 20tons in total.
Even if it's a 100km high airburst, that's got to do *something* rather nasty.
-
All that being said, isn't atmospheric density an issue there as well? Trace atmospheres don't have a 1atm density, so conceivably you could have an actual surface kinetic strike.
Flip side to that, when you have higher density atm, say 3 or 4, the high altitude dissipation is greater, but the overpressure wave for anything that gets down the air column is going to be... nasty...
-
All that being said, isn't atmospheric density an issue there as well? Trace atmospheres don't have a 1atm density, so conceivably you could have an actual surface kinetic strike.
Flip side to that, when you have higher density atm, say 3 or 4, the high altitude dissipation is greater, but the overpressure wave for anything that gets down the air column is going to be... nasty...
Atomospheric conditions being stirred up by quite a bit in this situation could be well very nasty indeed to what specific data sets im not sure but a consideration on this point yes
-
All that being said, isn't atmospheric density an issue there as well? Trace atmospheres don't have a 1atm density, so conceivably you could have an actual surface kinetic strike.
Flip side to that, when you have higher density atm, say 3 or 4, the high altitude dissipation is greater, but the overpressure wave for anything that gets down the air column is going to be... nasty...
This is true. However, there are several factors at play here. First, the fact that a planet with lower gravity is going to suffer less. Why? The depth of the atmosphere is a function of the gravity of the planet. At some altitude, Mars had a denser atmosphere then that of Earth. For a given velocity, a projectile will break up at a given density, so for constant surface pressure, you're better off on a low-G world. Note that this is for a given sea-level pressure.
I don't know terribly much about shockwave propagation, but based on a little research (Effects of nuclear weapons) it appears that for a given blast, overpressure is directly proportional to ambient pressure. I'm not sure how various losses would effect the shockwave at different pressures.
-
The first part is entirely correct, but I'm not so sure about the last part of your statement. Momentum in this situation is almost negligible. Once the projectile breaks up, the sectional density goes way down, dumping energy/momentum even faster. Almost all movement in this case is going to come from the heated air, which will be moving in all directions. I don't see it "rebounding" at all.
And I'm even more skeptical of the person you quoted, given that he got just about everything else completely wrong.
Didn't worry about anything else in the post, just saves on typing to copy what is right.
And as for the rebound (actually reflection) of the shockwave, it will happen. There aren't any studies of it for high energy shockwaves in atmosphere, but lots of them for the shockwave of sound as it travels in water and hits the different temps/densities. Tracking something with sonar depends alot on where it is in the layers of water.
The tropopause should reflect a fair amount of energy back into the high atmosphere as the low density air above it runs into the much higher density air below. But what percentage is reflected is anyones guess.
This is true. However, there are several factors at play here. First, the fact that a planet with lower gravity is going to suffer less. Why? The depth of the atmosphere is a function of the gravity of the planet. At some altitude, Mars had a denser atmosphere then that of Earth. For a given velocity, a projectile will break up at a given density, so for constant surface pressure, you're better off on a low-G world. Note that this is for a given sea-level pressure.
Only to a degree does gravity impact density of atmosphere. Titan (moon of Saturn) has only a fraction of Earth gravity but its atmosphere is actually denser than Earth's. It is about 40% more dense as I remember.
But as a general rule, it is true that lower gravity will have lower atm density.
I don't know terribly much about shockwave propagation, but based on a little research (Effects of nuclear weapons) it appears that for a given blast, overpressure is directly proportional to ambient pressure. I'm not sure how various losses would effect the shockwave at different pressures.
How it propagates is anyone's guess on this one. The thought of how dense the atmosphere will have to be to stop a projectile could be a nightmare. A rare atm might disrupt the missile but still be thin enough to allow the plasma to reach the surface. This one is way over my head...
-
SHoemaker levy into jupiter serves as a real world example though they were much larger and falling into a gas atmosphere
-
Thermal conduction limites the rate at which the missile will be destroyed, and coversion of the missile into a plasma strike in the atmosphere is irrelevent to the planet underneath it the energy contained in the missile will arrive on the surface as its momentum is so great, it will not "bounce." The atmosphere is not a factor (unless you live in a gas giant). The missile plasma is the equivelent of a high energy particle beam weapon in this case.
This is true for anything moving at 0.1c and upwards. At that speed a missile hitting a ship is an instant kill of the vessel struck. Even a ship of 100,000 tonnes hit by a 20 tonne missile moving at 0.1c will be destroyed instantly. The missile and ship will merge and the resulting body will be instantly (in under 0.1 ms) be accelerated to the velocity of (20*30,000 km/s)/(100000+20)= 6 km/s. 6000 m/s/0.1 ms is an acceleration of 6x10^7 m/s2...or 6 million gravities. The ship collapses structurally and the crew is rendered into paste. In reality I would assume the missile blows through the ship and the amount of energy and momentum transfered to the target ship is less but it probably bends like a pretzel and the crew is again rendered into paste by the 1000 G's or so.
Normal planetary velocities are under 50 km/s. And asteroid strikes and such are probably at a velocity that is lower since the object is usually moving in a spiral rather than directly inwards and it becomes a case of relative velocity (which can make it worse for head on collisions).
For a working newtonian motion system you probably could look at the game "Attack Vector: Tactical" by Ad Astra. They have a set of full newtonian rules.
-
And as for the rebound (actually reflection) of the shockwave, it will happen. There aren't any studies of it for high energy shockwaves in atmosphere, but lots of them for the shockwave of sound as it travels in water and hits the different temps/densities. Tracking something with sonar depends alot on where it is in the layers of water.
The tropopause should reflect a fair amount of energy back into the high atmosphere as the low density air above it runs into the much higher density air below. But what percentage is reflected is anyones guess.
When I wrote that, I was thinking about the physical projectile, not the shockwave. So yes, some would be reflected.
Only to a degree does gravity impact density of atmosphere. Titan (moon of Saturn) has only a fraction of Earth gravity but its atmosphere is actually denser than Earth's. It is about 40% more dense as I remember.
But as a general rule, it is true that lower gravity will have lower atm density.
That was not my point. My point was that a low-gravity world with the same sea-level pressure will have a thicker atmosphere. And if the world in question is terraformed to match earth at sea level, then it will absolutely have the same density.
How it propagates is anyone's guess on this one. The thought of how dense the atmosphere will have to be to stop a projectile could be a nightmare. A rare atm might disrupt the missile but still be thin enough to allow the plasma to reach the surface. This one is way over my head...
I'm not sure either. Maybe in a few years...
SHoemaker levy into jupiter serves as a real world example though they were much larger and falling into a gas atmosphere
Also, not traveling at remotely the same speed. No comparison.
Thermal conduction limites the rate at which the missile will be destroyed, and coversion of the missile into a plasma strike in the atmosphere is irrelevent to the planet underneath it the energy contained in the missile will arrive on the surface as its momentum is so great, it will not "bounce." The atmosphere is not a factor (unless you live in a gas giant). The missile plasma is the equivelent of a high energy particle beam weapon in this case.
Every one of these statements is false. First off, the missile is likely to be destroyed by physical stress, not just heating. Dynamic pressures on the order of terapascals. In the upper atmosphere. Secondly, the amount of heat released is so large that I'm going to assume that it will be destroyed by heating unless you can show me the calculations that prove otherwise. Thirdly, the momentum is not great at all. The kinetic energy to momentum ratio is absurdly high, and that's what matters. Technically, it does have a lot of momentum, but that's like claiming that an artillery shell has a lot of momentum, so after it goes off, the gas cloud should still be able to penetrate things. Lastly, the plasma will want to expand out the sides. Nothing is stopping it. Maybe I should put this another way. I've done the math (a page or two back) to support my position. Do the math to support yours. Things like heat transfer, and why it doesn't just break up. Also, why the plasma doesn't expand into a cloud, which rapidly dumps its momentum into the atmosphere.
This is true for anything moving at 0.1c and upwards. At that speed a missile hitting a ship is an instant kill of the vessel struck. Even a ship of 100,000 tonnes hit by a 20 tonne missile moving at 0.1c will be destroyed instantly. The missile and ship will merge and the resulting body will be instantly (in under 0.1 ms) be accelerated to the velocity of (20*30,000 km/s)/(100000+20)= 6 km/s. 6000 m/s/0.1 ms is an acceleration of 6x10^7 m/s2...or 6 million gravities. The ship collapses structurally and the crew is rendered into paste. In reality I would assume the missile blows through the ship and the amount of energy and momentum transfered to the target ship is less but it probably bends like a pretzel and the crew is again rendered into paste by the 1000 G's or so.
That's a good point, but I'm not totally sure how true it is. Anything under 6 million Gs will probably fail. And that includes the parts adjacent to the impact. Those pull off, and go spinning through the ship sowing destruction, but also sharply increasing the momentum transfer time. On the other hand, it's a good reason not to use armor. On the gripping hand, 30 tons is very, very big for an antiship weapon under these circumstances,
Normal planetary velocities are under 50 km/s. And asteroid strikes and such are probably at a velocity that is lower since the object is usually moving in a spiral rather than directly inwards and it becomes a case of relative velocity (which can make it worse for head on collisions).
For a working newtonian motion system you probably could look at the game "Attack Vector: Tactical" by Ad Astra. They have a set of full newtonian rules.
Asteroid strikes generally are under 50 km/s, but so is everything else. I'm sure I could find a velocity distribution if I really wanted to, but those operate in an entirely different realm.
And I own a copy of AV:T.
-
I posted a thread about this particular problem on XKCD fictional science.
Wardraft's post there includes some lower bound estimates on how much the projectile would expand outwards (5tons at 60kkm/s relative)
http://forums.xkcd.com/viewtopic.php?f=59&t=80213#p2888555
Obviously, his estimates are riddled with assumptions but he errs on the side of greater penetration so the projectile ought to explode somewhere above where he puts it.
The conclusion is that the projectile will not reach the surface.
Is there any kind of test on how high-altitude nuke-like explosions work? Especially focusing on how the shockwave propagates downwards?
-
Nothing on this scale. None of the nuclear weapons tests that I know of were at the right size and altitude. Only a few were high-altitude, and those were too high. I'm looking up more data.
The analysis you posted agrees with my gut. It's simply not going to reach the ground. I need to figure out how the expansion rate would be calculated. Someone around here has to know.
-
My gut ration is to agree that the missile won't reach the ground, but if the expansion rate was limited by the speed of sound then a heavy enough missile could actually do it.
The speed of sound in a solid seems to range from 3,000 m/s to 5,000 m/s. A 30 ton missile (50% fuel mass burned to accelerate) has a target cross section radius of 2.78 m.
To figure out what would happen if this 0.1c missile broke up at 90 km and was limited to a 4 km/s expansion rate, I dumped the problem into a spread sheet for a discrete method solution with 5-10km steps. The resulting mass didn't slow to less than the expansion rate until 2km above sea level. If it had hit a 6 km tall mountain, it would have been a 138m radius mass of mostly supper heated compressed air moving at 29 km/s with 0.1% of the original kinetic energy (6.5PJ)
A slower expansion rate would have hit the ground. A faster expansion rate or earlier break up wouldn't hit any mountains.
If anyone wants a planet killer, they'll probably need the mass and momentum of an entire suicide-ship, and not just a fast missile.
I can't remember seeing anyone's math on structural acceleration-related failure, so for what they're worth here are my "yes, it will pancake" calculations.
Acceleration = F/m. Force/area = stress. mass=density*volume. Max_Accell = Ultimate_Stress/(density*length)
Also
Acceleration = ?V/?T. ?V = V*?m/mass -> accell = V*m'/mass. m'=area*air_density*speed, so A=V^2/(density*length)
Equate the two accelerations, material density and length cancel, and Vmax = sqrt(ultimate_stress/air_density)
A strong solid metal alloy (400 MPa) vs 1g/m3 air will squash itself at anything above 633 km/s even without the help of heating. A trans-Newtonian alloys sold slug 25x stronger will shatter against the atmosphere at impacts over 3200 km/s.
-
I'm going to try to get a better handle on the expansion speed, or at least the speed of sound. First off, I'm using c=sqrt(1.6667 R*T /M). Now, for the first instant. Assuming that all of the iron is instantly converted to plasma, and assuming the xkcd numbers and all of the energy dumped into the iron particles as kinetic energy, the temperature should be 4.8e6 K. Assuming all of that, the speed of sound comes out to 34,660 m/s. I have no doubt that the above analysis is riddled with errors, but it should be accurate to within a factor of two or so (I hope). I'm not sure how it would change with time. As the projectile slows, it picks up particles, but releases energy. After the next 10 km (using his numbers), and hoping I've done the math correctly, it should have a speed of sound of somewhere between 1,964 km/s (density of iron) and 1,389 km/s (half the density of iron). Based on that, I think the expansion will be significantly faster then previously expected, at least at first.
Oh, and I did the acceleration-related failure earlier in the thread. I can up with something around (I think) 2 TPa at 50 km for .2 c, which will pulverize anything, regardless of heating.
Edit:
Looking more at high-altitude nukes, I'm starting to think that, for smaller objects, the fireball might well be the biggest contributor to damage. It's going to be very, very hot, and radiation from that will start fires and such. The blast wave from all of the various high-altitude tests appears to have been negligible. None of them were in the same region as we're looking at. The closest were Hardtack Oak, Orange, and Yucca.
-
Bluegill Triple Prime was 410kt at 48km altitude. Caused retinal burns on 2 unshielded workers.
And that Orange event you mentioned was 3.8mt at 43km altitude, producing 3 cal/cm^2 thermal radiation at ground zero.
Source: (search for Wednesday, March 29, 2006)
http://glasstone.blogspot.com/2006/03/checkmate-detonation-as-seen-from.html
Doesn't tell you much though. You can't just simply scale it up to the hundred megaton range that would be expected of most anti-planet kinetic weapons. Atmospheric absorption is certainly going to be different at the kind of temperatures a kilocal/cm^2 radiation level would cause
-
Bluegill Triple Prime was 410kt at 48km altitude. Caused retinal burns on 2 unshielded workers.
And that Orange event you mentioned was 3.8mt at 43km altitude, producing 3 cal/cm^2 thermal radiation at ground zero.
Source: (search for Wednesday, March 29, 2006)
http://glasstone.blogspot.com/2006/03/checkmate-detonation-as-seen-from.html
Doesn't tell you much though. You can't just simply scale it up to the hundred megaton range that would be expected of most anti-planet kinetic weapons. Atmospheric absorption is certainly going to be different at the kind of temperatures a kilocal/cm^2 radiation level would cause
Oops, I guess I missed that one. However, I'm not certain that atmospheric absorption will be all that different. Why would it be? For one thing, the overall situation is similar, and we have data on propagation of those sorts of flux. It's just from bombs closer to the ground. Secondly, for all intents and purposes the atmosphere is transparent at the frequencies in question. Yes, they might not propagate perfectly, but this isn't a laser.
-
But that much energy being dumped might cause the air to breakdown into plasma, ala laser blooming effect. 's why anti-ship lasers don't work against planets, even if the frequency was changed to microwaves.
Oh but then again...
Nvm, found a neat source:
http://nuclearweaponarchive.org/Nwfaq/Nfaq5.html
Haven't read it all, but it might appear that getting these bits:
- the size of the shockwave when at 5psi as a function of yield
- % energy in thermal radiation and length of pulse (to calculate wattage per cm^2 at specific ranges)
And then back calculating the yield (and hence KE) of the kinetic missile to get the minimum parameters for:
1) Thermal energy under impact site to destroy wood/concrete/iron
2) Shockwave to reach ground
Would go a long way to estimating the relative damage of kinetic missiles. Assuming we can take a burst height of ~50km?
EDIT:
Found this under 5.6.1.1 Thermal Injury:
Convenient scaling laws to allow calculation of burn effects for any yield are:
r_thermal_1st = Y^0.38 * 1.20
r_thermal_2nd = Y^0.40 * 0.87
r_thermal_3rd = Y^0.41 * 0.67
Range is in km, yield is in kt; the equations are accurate to within 10% or so from 1 kt to 20 Mt.
-
Maybe. However, I'm fairly certain that any equation that gives you pressure as a function of burst radius or vice versa will assume that both are at or near sea level unless it mentions otherwise.
For an authoritative source on the subject, try: http://www.fourmilab.ch/etexts/www/effects/.
-
How does the http://en.wikipedia.org/wiki/Tunguska_event relate to your calculations? (directed to everybody)
I realize it was most likely going slower than the kind of projectiles you folks are talking about, but if it really was only tens of meters across then my thought would be to just drop a smeg ton of them out of a ship and then let gravity do the rest. Obviously the slower the object the easier it is to intercept, but dumping a couple hundred of them could start to get dicey for the defenders, no?
I am not a mathematician, so feel free to tell me I am orders of magnitude outisde the conversation :)
-
How does the http://en.wikipedia.org/wiki/Tunguska_event relate to your calculations? (directed to everybody)
I realize it was most likely going slower than the kind of projectiles you folks are talking about, but if it really was only tens of meters across then my thought would be to just drop a smeg ton of them out of a ship and then let gravity do the rest. Obviously the slower the object the easier it is to intercept, but dumping a couple hundred of them could start to get dicey for the defenders, no?
I am not a mathematician, so feel free to tell me I am orders of magnitude outisde the conversation :)
Pretty much.
Nobody is claiming that Tunguska-type weapons are useless. The current discussion is about objects going three orders of magnitude faster, which puts them in an entirely different range of energies, which leads to different altitudes and burst effects. However, if you just want to flatten an area, a nuke is easier and cheaper then moving a few hundred or thousand tons of rock. (Yes, I understand about sorium's energy density. The problem is how deep and fast you can get something without it blowing up. And moving asteroids is very difficult. Someone posted "rocks are not free, citizen" early in the main thread.) And remember that a few tens of meters may not sound like much, but given that volume is equal to length cubed, and we're dealing with something more dense then water, it adds up fast.
-
I'd just dump a tanker in the atmosphere and let it rain fire.^^
Psych ftw. ;D
As a more serious question, what would a "Planetkiller" weapon try to achieve?
Deal serious damage on the ground?
Kill the Atmosphere?
Kill all inhabitants?
Or actually damaging the planet?
-
As a more serious question, what would a "Planetkiller" weapon try to achieve?
Deal serious damage on the ground?
Kill the Atmosphere?
Kill all inhabitants?
Or actually damaging the planet?
Guess it would depend on your goals. And how much you were willing to invest in 'rebuilding' or if you were willing to write it off for the safety of your race.
If the race isn't a major threat, damaging them enough that they have no ability to resist you would be enough.
If they could push you into extinction, then you had better beat them to the punch.
On the thought of killing a planet...I doubt the game has ever even addressed what it would take to be a 'crust buster' or such. Rendering orbital bodies into debris is a pretty tall order....
-
Deal serious damage on the ground?
I'll be satisfied with this. Nuke-like effects without radiation fallout and logistical simplicity.
-
As a more serious question, what would a "Planetkiller" weapon try to achieve?
Deal serious damage on the ground?
Kill the Atmosphere?
Kill all inhabitants?
Or actually damaging the planet?
All of these are possible to some extent. The current RKV-light under discussion would be a super-nuke, with a damage radius on the order of hundreds of kilometers. Bigger objects would likely kill the planet, but the problem is getting them there. Unless, of course, Steve allows us to shove them out of transports.
-
Don't think you want to kill planets anyway. Just remove the... inconvenient biologicals. =)
EDIT: late game, when it is possible, perhaps you might want to frag some moon somewhere to make a point, but even then I doubt that sort of thing will be used even as a last resort.
The idea is to develop a different way to nuke planets besides slow and easier to intercept (relatively) nuke missiles. Cost effectiveness wise, I think the nukes and kinetics are in the same ballpark but I believe kinetic missiles will win out once past the early tech levels.
We shall just have to see when we get to play.
-
Ok how about smaller nuclear warheads or fusion warheads based on smaller impact and explosion but able to travel faster, perhaps if they get so far into the planet they might render some environmental damage or even a mini terraformer warhead full of gas canisters that might change an atmospheres composiition
-
Don't think you want to kill planets anyway. Just remove the... inconvenient biologicals. =)
That leaves two reason to kill a planet, then.
1. It's the easiest way to remove said biologicals.
2. It makes mining way, way, easier.
No, three reasons:
3. Fun
EDIT: late game, when it is possible, perhaps you might want to frag some moon somewhere to make a point, but even then I doubt that sort of thing will be used even as a last resort.
The idea is to develop a different way to nuke planets besides slow and easier to intercept (relatively) nuke missiles. Cost effectiveness wise, I think the nukes and kinetics are in the same ballpark but I believe kinetic missiles will win out once past the early tech levels.
We shall just have to see when we get to play.
Kinetics are excellent when you wish to destroy a couple hundred kilometers radius. Not so good if you just want to kill a city.
Ok how about smaller nuclear warheads or fusion warheads based on smaller impact and explosion but able to travel faster, perhaps if they get so far into the planet they might render some environmental damage or even a mini terraformer warhead full of gas canisters that might change an atmospheres composiition
Inside the planet itself? That would take an incredibly big warhead. And a kinetic is going to do all the environmental damage you'd ever want. That big of a heat pulse will not be a good thing, nor will any aftereffects from the shockwave.
-
I don't know that it would be easier to extract minerals from a planet you have killed. If you have wiped out the population then you can't use them as slave labor, also you have likely destroyed any of the facilities you could have re purposed. If by kill you mean break up the planet, I don't think it would be particularly easy to sort through a densely packed debris field that a broken planet would leave behind.
-
In that case a new asteroid field might form after a planet explosion ie planet killer
-
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,
-
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
-
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.
-
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.
-
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.
-
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).
-
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.
-
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.
-
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.
-
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.
-
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
-
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.
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.
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.
-
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.
-
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.
-
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.
And impacting at hypersonic speed it will make a nice hole in the ground.
A rod will do little else.
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.
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
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.
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.
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.