I know that past dicusssions of near-C rocks got so heated that the topic was banned from the Traveller Mailing List, so I am ask this with trepidation, but are there any canonical defenses against mass drivers?
Passive Planetary Defenses
- Thread starter Garnfellow
- Start date
Enoki
SOC-14 1K
This comes down to the question of "How much damage is one side willing to do to a planet to take it?"
If the world has resources or infrastructure that the side trying to conquer it wants then smashing everything whether with nukes, rocks, or some other weapons is going to be counterproductive. It defeats the purpose of taking the planet to begin with.
On the other hand, if the intent is simply to deny those resources to an enemy then busting the planet into an asteroid field is probably a good thing.
Oh, one thing that might be doable, given sufficient time, is to artificially grid the world with a set of rings. These would provide a means to prevent ships from entering orbits near the world. These would also provide some protection against incoming fire, missiles, etc. Of course, this requires more knowledge of how you could make it work than I have in astrophysics...
Not that has been mentioned the couple of other times it has come up.
MAD is pretty much the default assumption.
Personally, I PSB that it is essentially impossible to accurately calculate a jump vector for something going that fast, so the acceleration has to be "in system" which in turn allows any decent level tech system to detect the oncoming rock and deal with it accordingly.
D.
I can't help but wonder if the best defense against a kinetic kill weapon are other kinetic kill weapons.
For instance, someone decides to send the world back to its pre-atmosphere days with a big ripping planetoid towards a world it desires to rape/kill/destroy.
From the planet's perspective, a constant barrage of smaller asteroids sent on a glancing impact against the planetoid might have the same effect as using a water blaster on a ball that is rolling down hill towards a target. You can't stop the ball from rolling down the hill, but you can deflect it.
In the book series MUTINEER'S MOON - Earth is the target of such an attack (although not near C per se, but serious enough!) The "hammer" being sent against the demon sector nest killers (that's EARTH!!!) gets a protective screen of warships, while the planet advances towards earth.
Just thinking aloud...
For instance, someone decides to send the world back to its pre-atmosphere days with a big ripping planetoid towards a world it desires to rape/kill/destroy.
From the planet's perspective, a constant barrage of smaller asteroids sent on a glancing impact against the planetoid might have the same effect as using a water blaster on a ball that is rolling down hill towards a target. You can't stop the ball from rolling down the hill, but you can deflect it.
In the book series MUTINEER'S MOON - Earth is the target of such an attack (although not near C per se, but serious enough!) The "hammer" being sent against the demon sector nest killers (that's EARTH!!!) gets a protective screen of warships, while the planet advances towards earth.
Just thinking aloud...
Silverhawk
SOC-12
Possibly another venue for defense...
If one uses a really powerful beam weapon to bite into the oncoming asteroid or such, the "ablative" aspect of turning part of the asteroid into super heated gases might be the equivalent of using a low grade rocket engine. The exhaust from the super heated gases would likely push against the asteroid.
Question is: How much energy would be required to produce that effect? I'm thinking along the lines of High Energy Lasers being used to act as a ground based engine for heating plastic and having the vessel be propelled that way.
(Yes, taken from TRANSHUMAN SPACE from Steve Jackson Games)
If one uses a really powerful beam weapon to bite into the oncoming asteroid or such, the "ablative" aspect of turning part of the asteroid into super heated gases might be the equivalent of using a low grade rocket engine. The exhaust from the super heated gases would likely push against the asteroid.
Question is: How much energy would be required to produce that effect? I'm thinking along the lines of High Energy Lasers being used to act as a ground based engine for heating plastic and having the vessel be propelled that way.
(Yes, taken from TRANSHUMAN SPACE from Steve Jackson Games)
Three of the five needed data points:
http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html
http://www.engineeringtoolbox.com/latent-heat-melting-solids-d_96.html
http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html
In system equilibrium temp is, in ecosphere, 273°-325° K, we'll use 300° K...
Iron: Around 1500° K, so needing ∆T=1200°
kJ/kg = ∆T * Hs +Hlv
kJ/kg = 1200 * 0.45 + 209
kJ/kg = 540 + 209
kJ/kg = 749
call it, rounded 0.75 MJ per kg, and SG is 7-ish...
so 5.25 MJ/L
Now, we need to convert that to pressure... and that's where I know the basic ideas but not the math. We need the vaporization expansion coefficient for iron, and the conversions to thrust on target.
It's not going to be an efficient conversion to thrust.
Well, if you want to set some limits, you can declare that there's some effect to very high velocity in jump space and that ships entering jump space past a certain very high velocity simply don't emerge. That at least limits them to postulating some way of doing it in the opponent's own system, which is still a headache but at least leaves some chance that the target can develop some system to detect and intercept such attacks while they're still far enough off that it would do some good.
The primary solution to the velocity problem is the 32 hour arrival window for jump. Space is big, and things move a lot in 32 hours, and when you show up, you simply don't know what time you arrive. You can't make a "ballistic" decision from out of system with a 32 hour discrepancy on the other end.
The faster you come in, the more difficult it is to potentially correct your course based on your arrival.
Now, given that, you could always simply bracket the target. Send 100 things through jump simultaneously, since 3% of them will "hit the target" as planned. But that certainly makes the logistics more difficult.
I thought it was 6 to 8 days with a 2/3 chance of hitting 7.
Anyway, lessee...
Earth moves about 30 kps through its orbit. You've got a 32 hour window, so it moves 3.456 million kilometers in that time. You need to have enough time to adjust laterally half that distance before impact. I will assume you've already matched speed. So, at 1G, 18,590 seconds - 5 hours. Limits top speed to under 70 kps. At 6g it's a good deal better, but not earth-shatteringly better; we're talking a newsworthy crater maybe, but nowhere near E.L.E. territory. If I did my math right, the free trader comes in around 1/3 ton TNT equivalent, larger ships correspondingly more powerful, faster ships more powerful still, but a small nuke still packs more punch.
Okay, I see that.
Let's check your math...
4.184e6 J per gram for TNT
Impact Joules = kg * v^2.
3.456e9 m transit.
Earth diameter 1.2742e7m
100D limit 2.5484e9m diameter sphere...
Distribution is pretty close to standard ... so putting that as a percentage... 73% of the range, but probably 90% of the jumps. We can use the 100D limit, instead.
Note that it's a 6d6 roll, so standard deviation is (per Anydice) 4.18... 31 hour range is thus ±3.708 sigma, and the variability is 22.6 hours worth to hit the sphere in the ±2.7
halving that, 1.28e9 m (rounding up)... looking it up, that's 87%...
: d = 0.5AT^2
: 2.54e9= AT^2
@1G:
: : 2.54e8 = T^2
: : 1.59e4 sec minimum transit time.
Converting to maximum velocity to allow impact
: : Vmax = D/T
: : Vmax = 1.28e9/1.59e4
: : Vmax = 8.05e4 m/s
Energy of impact
: : Scoutship is about 500 Mg (megagrams = Metric Tons)
: : Emin = Vm^2 * Mass
: : Emin = 8.05e4^2 * 5.0e11
: : Emin = 6.48e9 * 5.0e11
: : Emin = 3.24e21 J
Converting into TNT
: : 3.24e21 J / 4.184e6 (J/g)
: : 774378585086042.1 J
: : 7.74e14 g TNT
: : 7.74e11 kg TNT
: : 7.74e8 Tons TNT
: : 7.74e5 kilotons TNT
: : 7.74e2 Megatons TNT
so 774 Megatons of TNT.
The closer to the center you are, the more you can burn in...
13% of the time, you miss horribly... but can reasonably claim you simply had navigational issues.
Now, with 6G
: 2.54e9= AT^2
@6G
: : 4.23e7 = T^2
: : 6506 = T
: : Vmax = 1.28e9/6.506e3
: : Vmax = 196741 = 1.97e5 m/s
: : Emin = 1.97e5^2 * 5e11
: : Emin = 1.94e+22
: : g TNT = 4625622106444462 = 4.63e15
: : g to Mg aka Tonnes TNT (e-6): 4.63e9 Tonnes
: : to MT: 4.63e6 tons...
to GT 4630 GIGATONS of TNT.
And keep in mind: the closer you hit to center, the less re-aim, and the more boost in.
4.184e6 J per gram for TNT
Impact Joules = kg * v^2.
3.456e9 m transit.
Earth diameter 1.2742e7m
100D limit 2.5484e9m diameter sphere...
Distribution is pretty close to standard ... so putting that as a percentage... 73% of the range, but probably 90% of the jumps. We can use the 100D limit, instead.
Note that it's a 6d6 roll, so standard deviation is (per Anydice) 4.18... 31 hour range is thus ±3.708 sigma, and the variability is 22.6 hours worth to hit the sphere in the ±2.7
halving that, 1.28e9 m (rounding up)... looking it up, that's 87%...
: d = 0.5AT^2
: 2.54e9= AT^2
@1G:
: : 2.54e8 = T^2
: : 1.59e4 sec minimum transit time.
Converting to maximum velocity to allow impact
: : Vmax = D/T
: : Vmax = 1.28e9/1.59e4
: : Vmax = 8.05e4 m/s
Energy of impact
: : Scoutship is about 500 Mg (megagrams = Metric Tons)
: : Emin = Vm^2 * Mass
: : Emin = 8.05e4^2 * 5.0e11
: : Emin = 6.48e9 * 5.0e11
: : Emin = 3.24e21 J
Converting into TNT
: : 3.24e21 J / 4.184e6 (J/g)
: : 774378585086042.1 J
: : 7.74e14 g TNT
: : 7.74e11 kg TNT
: : 7.74e8 Tons TNT
: : 7.74e5 kilotons TNT
: : 7.74e2 Megatons TNT
so 774 Megatons of TNT.
The closer to the center you are, the more you can burn in...
13% of the time, you miss horribly... but can reasonably claim you simply had navigational issues.
Now, with 6G
: 2.54e9= AT^2
@6G
: : 4.23e7 = T^2
: : 6506 = T
: : Vmax = 1.28e9/6.506e3
: : Vmax = 196741 = 1.97e5 m/s
: : Emin = 1.97e5^2 * 5e11
: : Emin = 1.94e+22
: : g TNT = 4625622106444462 = 4.63e15
: : g to Mg aka Tonnes TNT (e-6): 4.63e9 Tonnes
: : to MT: 4.63e6 tons...
to GT 4630 GIGATONS of TNT.
And keep in mind: the closer you hit to center, the less re-aim, and the more boost in.
mike wightman
SOC-14 10K
Kinetic energy should be half that
E=1/2 m v^2
E=1/2 m v^2
And then there are the T5/MgT ships capable of much higher acceleration... Assuming these arrive at the 100 diameter limit how long do you have to react? At the speeds involved can they even maneuver? What's going to happen if you can intercept them with a large enough MAC (Mass Accelerator Cannon aka railgun but spinal mount sized) round?
mike wightman
SOC-14 10K
Lol, yup.
At the energies you have calculated the outcome is pretty traumatic.
I've often wondered if the ship would actually make it to surface impact or would it be a ball of plasma slamming into the ground or exploding in the air.
There have been some pretty interesting studies done on the angle of attack of asteroid impacts and how the closer the impact is to 90 degrees the les atmosphere there is to penetrate and hence the greater chance of a ground impact and a commensurate increase in devastation potential.
Yep, left off some zeroes. Feeling pretty stupid. 
Yep, left off some zeroes. Feeling pretty stupid.
There's a reason I do the math on the board - So someone can check my work.
noting that the difference between 1G and 6G is 3.5 orders of magnitude... (0.4 GT vs 2 TT tnt)... that was a surprise. That's for a Scout Courier... A battleship will be about 10 PetaTons.
Lesson learned: doing math on the fly while busy with something else is a bad idea.
So we're back to forces that, even with a scout or free trader purloined by some terrorist group, pack enough wallop to plow most or all the way through crust to magma and, if nothing else, trigger planetwide earthquakes that would level cities, planet-enveloping ash clouds that would devastate the world's ecology, and a planetwide barrage of re-entering fiery debris - all of which can partly be averted by inventing some rationalization for limiting top speed when entering jump.
So we're back to forces that, even with a scout or free trader purloined by some terrorist group, pack enough wallop to plow most or all the way through crust to magma and, if nothing else, trigger planetwide earthquakes that would level cities, planet-enveloping ash clouds that would devastate the world's ecology, and a planetwide barrage of re-entering fiery debris - all of which can partly be averted by inventing some rationalization for limiting top speed when entering jump.
So, I'm still curious, what happens if you manage to intercept one of these ships with a spinal mount sized chunk of dense material moving at a high speed? Would they vaporize before hitting the planet? How long do you have to react assuming detection of jump exit?
