Crashing ships as weapons

[esampson]

I was estimating it at 2,000,000 tons, so for the point of illustration my figures are still good. It's 2% of the energy instead of 1%. Still just a tiny fraction.

And no, the Chicxulub asteroid may have triggered the extinction of about 75% of the species on the planet. However there are a lot of theories that it was not solely responsible and even if it was it did not kill them immediately. The die off occurred because the impact created massive climate disruptions that caused the food chain to collapse. There was no one to attempt species conservation or climate modification such as there would be if Earth had been a planet of the Imperium.

Again, I'm not saying the Tigress crashing at .01c wouldn't be a horrendous event. It absolutely would be, especially if it was crashed with the intention of causing the most damage possible. I'm just putting the amounts of energy into perspective and saying it wouldn't be a 'planet splitter' or even a 'planet killer'. With the energy of 1/50th of the energy of the Chicxulub asteroid life on the planet would certainly be disrupted but I can't imagine it would be wiped out.

 

[Blue Ghost]

You're forgetting kinetic energy. Forget fuel mass for a minute (I've been assuming Traveller had reactionless drives, which decreases the required mass by a lot, but sure, you still need fuel to move). The ship is converting fuel to velocity, which is kinetic energy, which is 1/2 mv^2 joules (for m in kg and v in m/s).

If we get our ship up to a paltry 0.01c before impact, that's 0.5 * m * (2.998e+8 m/s / 100)^2 = 4.5e+9 joules of energy per kg of mass of the ship. Smash that into a planet.

At 2% of the speed of light, that quadruples the kinetic energy. At 3%, 8 times the joules. And so on.

Well, off the top of my head you need to use the relativistic equations because things "change" at those speeds.

I guess it's one of those things where it looks good on paper, but the reality may be something a little more prosaic than what your figures describe. Objects travelling at relativistic speeds tend to punch through other objects, or get absorbed. At least that's what I recall from both high school and college engineering physics. My brain's a little hazy on that.

 

[Blue Ghost]

Except that when you are using such modes you do not theoretically increase the kinetic energy of the ship. The same bit of physics trickery that allows the ship to 'exceed' the speed of light also prevents it from gaining massive amounts of kinetic energy (essentially, because space is being warped the ship itself is not moving or is moving at a more reasonable subluminal velocity).

Now what the effect of the space warping field is when it intersects a planet is a whole different matter of conjecture, but for right now and for the purposes of a game we could easily handwave it away and say that when the field intersects a massive body the physics cause the entire field to collapse making the ship vanish. Thus suicide runs on planets would result in nothing at all happening to the planet but the ship vanishing from normal space never to return.

That's a bit beyond talking about how the Imperium might handle such things, however, because in the canonical Traveller universe ships don't use such a drive.

Yeah, you know, I've never seen anyone address that. It seems like the Alcubierre drive, for it to work, essentially takes your patch of reality, and places it outside the universe, which means that you slide through nebula, stars, planets of all sorts, clouds of matter, and whatever else that's out there, because you're "not really there", just traversing the same geographic dimension.

I don't know. It's been a while since I read on the subject. I saw a couple of videos on the topic recently, but nothing explaining the math, and certainly nothing to quote in a post here.

 

[esampson]

Well, off the top of my head you need to use the relativistic equations because things "change" at those speeds.

I guess it's one of those things where it looks good on paper, but the reality may be something a little more prosaic than what your figures describe. Objects travelling at relativistic speeds tend to punch through other objects, or get absorbed. At least that's what I recall from both high school and college engineering physics. My brain's a little hazy on that.

The formula for relativity effects is (basically) √(1-(V²/C²)). At .01c you might be able to measure the effect if you have good enough instruments but it would be pretty difficult. While you might have to make some adjustments to deal with relativity if you are getting up to .1c (especially if long periods of time such as several days are involved) you're probably not going to be getting any kind of serious relativistic effects until you are well past .5c. At .85c you are basically at the 2:1 point (time travels at only half the rate for the accelerated object and its mass is doubled).

 

[esampson]

Yeah, you know, I've never seen anyone address that. It seems like the Alcubierre drive, for it to work, essentially takes your patch of reality, and places it outside the universe, which means that you slide through nebula, stars, planets of all sorts, clouds of matter, and whatever else that's out there, because you're "not really there", just traversing the same geographic dimension.

I don't know. It's been a while since I read on the subject. I saw a couple of videos on the topic recently, but nothing explaining the math, and certainly nothing to quote in a post here.

I believe the Alcubiere drive actually stretches and squashes space (as proposed). It doesn't really place you outside the universe so you would not be able to just slide through planets or stars. You might be ok with nebula since the kinetic energy of the ship isn't increased.

 

[kilemall]

Again, I'm not saying the Tigress crashing at .01c wouldn't be a horrendous event. It absolutely would be, especially if it was crashed with the intention of causing the most damage possible. I'm just putting the amounts of energy into perspective and saying it wouldn't be a 'planet splitter' or even a 'planet killer'. With the energy of 1/50th of the energy of the Chicxulub asteroid life on the planet would certainly be disrupted but I can't imagine it would be wiped out.

Plutonium in the nuke warheads might though.

 

[esampson]

Poking around a lot it seems like a nuclear missile for Traveller fired from a bay is about 1 megaton yield. Now the Tigress does have 430 bays but still, we have detonated a 50 megaton bomb on Earth without any significant effect (except to the extremely local area).

Yes, I realize that the ship may carry additional missiles to reload the bays but we are still talking about orders of magnitude. The 50 megaton bomb that we detonated contaminated an area that is so relatively small that if you were in a position where you could see half of the earth in a glance you probably would be unable to see the area even if it was clearly marked. The number of missile bays makes that one order of magnitude larger so you might be able to see it as a pinpoint sized dot on the planet. If you had 4300 missiles on the Tigress that would be another order of magnitude. Now it might be a dot on the planet that actually has some sort of visible dimensions instead of being a speck, but you still aren't talking about anything even remotely approaching covering the planet.

Of course that's actually detonating the missiles, which isn't really going to happen when the ship crashes. What you're really looking at is the amount of radioactive material those missiles contain. Well, poking around the web for a bit in a manner that will quite likely get the NSA looking at me again it looks like it takes around 50 kg of material to make a 1 megaton explosion. That's about 21.5 tons for 430 missiles multiplied by however many times the bays can be reloaded and fired. That might seem like a lot but spread over the surface of a planet it's not going to be anything at all (about 40 milligrams per square kilometer for an Earth sized planet).

And of course all that is based on our TL of 8. I would assume that the missiles used by the Imperium are probably much more efficient and need much less fissionable material (while I don't assume the Imperium is able to achieve total matter to energy conversion it is still useful to note that the mass could be as small as about 50 kg for 430 missiles). Additionally, probably not all the missiles that a Tigress carries are nuclear. While only Imperial ships are allowed to use nuclear weapons I would guess that they carry conventional warheads as well in the exact same way that our own military has a mix of nuclear and conventional weapons.

The long and short of it is that killing a planet is hard. I'm not saying that crashing a ship into a planet at a substantial portion of the speed of light won't do it because the kinetic energy increases with the square of the speed (though there is an issue that having the kinetic energy isn't the only part of the equation, the energy must be delivered). What I'm saying is that you aren't likely to be doing it with things like the missiles carried on a ship (even a dreadnought) or by some halfhearted collision where the ship hasn't been accelerating for days if not weeks.

And once again, I'm not saying the impact wouldn't be a catastrophe, either. I'm just saying it wouldn't be some kind of world ending event.

 

[esampson]

Just as a side note to this entire conversation, I went ahead and did the math for a scout ship (assuming a scout ship has a mass of about 400 tons) travelling at .5c (something that would take nearly 6 months to accelerate to) and came up with 5e+21 joules of energy, and that includes accounting for the increased mass due to relativity. That is still only 5% of the estimated energy of the impact of the Chicxulub asteroid..

So while ships crashing into planets at high speed might be something terrorists would attempt and would still be something that people have to be concerned about I don't think they are quite the issue we are making them out to be. Governments would probably be about as likely to use these as they are to use things such as car bombs.

 

[esampson]

As a final aside I found this (http://impact.ese.ic.ac.uk/ImpactEffects/). I've got no idea how accurate it really since it is designed to simulate asteroids under less extreme situations but just for fun I fed in the numbers that should equate to a scout ship at .5c (http://impact.ese.ic.ac.uk/cgi-bin/...vel=149900&theta=90&tdens=3000&tdens_select=0). I used TNE for the mass of the ship (and used the loaded mass) and calculated density by dividing it by 1350 cubic meters and then calculated the diameter of a sphere with a volume of 1350 cubic meters.

You will do substantial damage out to around 500 kilometers of the epicenter so such an action would probably kill millions if you aimed at a population center but again, we aren't remotely in the area of the destruction people have been theorizing.

(Just to satisfy myself I also went ahead and ran the simulations using a density of 8000 kg/m³ with a diameter of only 5.5 meters and it still exploded in an airburst 30 km above the surface of the planet)

 

[JimMarn]

The science programs, doomsday possibilities, I have seen on this mention that ocean hits are the worst events. Is this true ?

 

[esampson]

It sort of depends on what you mean by 'worst events' but in most cases, probably yes. Ocean impacts by a sufficiently large impactor would have the problem of creating massive tsunamis. When this is combined with the fact that the majority of humanity tends to congregate along coastlines this can cause the loss of life to increase dramatically.

However, what I am now beginning to realize is that while a ship travelling at a large fraction of the speed of light carries a lot of energy it may not be able to effectively deliver that energy because it will explode in the atmosphere. It looks like the massive impactors in the past that have done so much damage were things travelling much slower but which were many, many orders of magnitude larger than even the biggest ships. Thus, a ship travelling slow enough to actually reach the ocean and transfer its energy into the water would probably not create a wave of any significant size (on a planetary scale).

I will have to admit, however, that I am way out on a limb here with my speculation on that. I'm not completely sold on the idea that a ship would detonate in midair since the formulas really are intended to model asteroids instead of ships. On the other hand I'm reminded of firing rifle bullets into water and seeing them absolutely disintegrate after only travelling a few inches.

 

[aramis]

The science programs, doomsday possibilities, I have seen on this mention that ocean hits are the worst events. Is this true ?

Depends.

Remember, it takes energy to change state, and impact energy becomes a mix of kinetic and thermal change.

Liquification of rocks takes a LOT of energy. Vaporization even more.

Hitting water, it's already liquid, and the vaporization is low energy. So, you get a LOT of water vaporized, plus an outward pulse of pressure, taking little of the overall energy, and THEN you get a slightly smaller ground impact. The kinetic causes and initial wave pulse, the fill-in & vaporization a second, the repeats potentially dozens more... a significant possibility of water lost to space and/or orbit, a huge amount in high altitude clouds, and then, admist it all, the rain of hot rock UNDER the thermal blanket of clouds...

Essentially, it adds tsunamis and reduces radiative losses at the same time vs a ground impact.

If the people aren't shoreline,and the planet's on the cool side, it's not always worse, per se - the temp comes up, and there's less direct damage. (If the temp comes up too much, tho')...
If it's on the hot side, it can feedback into a hothouse.

 

[Carlobrand]

...However, what I am now beginning to realize is that while a ship travelling at a large fraction of the speed of light carries a lot of energy it may not be able to effectively deliver that energy because it will explode in the atmosphere. ...

There's not much time to explode between atmosphere and ground at large fractions of c. That's not like a meteoric impact. That's more a situation where the ship is carrying velocities normally ascribed to particle accelerators. The interval between hitting atmosphere and impacting surface is short enough that even if the ship became a glob of plasma, it would barely even begin expanding before it struck the surface. I suspect the main reason it wouldn't deliver all its energy is because - beyond a certain velocity - it would be punching out the other side of the planet and into space.

 

[esampson]

There's not much time to explode between atmosphere and ground at large fractions of c. That's not like a meteoric impact. That's more a situation where the ship is carrying velocities normally ascribed to particle accelerators. The interval between hitting atmosphere and impacting surface is short enough that even if the ship became a glob of plasma, it would barely even begin expanding before it struck the surface. I suspect the main reason it wouldn't deliver all its energy is because - beyond a certain velocity - it would be punching out the other side of the planet and into space.

That was my initial impression but what I'm wondering is if hitting the atmosphere at such massive speeds the atmosphere itself won't act almost like a solid wall dispersing the plasma because the air can't get out of the way or be compressed fast enough.

Like I said, I'm not really sure that would happen. I think a lot of the formulas that the website are using are designed around things of looser composition than a starship and travelling at considerably slower speeds. However, I am also now not completely sure such a thing wouldn't happen (and to be honest I'm not sure there's anyone around who can be completely sure. I mean, how much research have people done in what happens to air when something rips through it at roughly 1 million times the speed of sound?)

 

[Carlobrand]

I don't think it's possible for atmosphere to act as a wall at such speeds. My understanding is the energy involved is of an order that atoms in the air and in the hull are being smashed. Mechanical properties become irrelevant. The individual molecules of nitrogen and oxygen are broken up, the individual atoms are smacked and accelerated and possibly broken into their constituents in the same way they would be if impacted in a particle accelerator - but this is happening along the entire surface of the front of the craft. Meanwhile, the individual atoms of the hull along that surface are likewise being slowed and possibly broken into their constituents as they transfer energy to the oxygen and nitrogen atoms - and then impacting the atoms of the hull behind them and being accelerated while those are slowed, and those slowed atoms impact the ...

I think you're looking at that region in front of the craft, and the hull itself, achieving pressures and temperatures normally found in the core of a sun. Momentum on that scale is not going to be denied by the mechanical properties of air nor by the mechanical properties of stone or magma.

 

[esampson]

Clearly the momentum would be denied by the mechanical properties of stone and magma because it was. Again, the Chicxulub impactor had 20 times that momentum and it was stopped (in fact it appears from what I've read that the estimated depth of the crater was 30 km which probably did not even breach the crust).

At any rate, I'm not saying that the ship would definitely explode in the atmosphere. I quite definitely recognize that the models being used may be flawed, especially as they were not designed for such things. However, I think that you should consider that the possibility exists that it might happen. Very strange things happen in fluid dynamics when you are dealing with things like that and sometimes the results are very counter intuitive.

Finally, even if the airburst doesn't occur and the ship slams into the ground you are talking about something with 1/20^th the energy of something that failed to wipe out life on the planet, and it took you 3 months to accelerate to that speed. It would appear that suicide diving ships, while being quite destructive, are not as destructive as we were initially considering them to be.

 

[JimMarn]

Interesting, thanks !

A different program showed an asteroid significantly larger, I don't remember the diameter, than the Chicxulub one. They said that such an impact would peel off the uper layers of the land depending on just how large it was. Suffiently large enough, and it would peel back the uppermost layers for several miles to most of Earth.

Apparently such a hit wouldn't take very long to wipe out everything, except maybe some bactyeria several miles down into the crust. So maybe we could get part of a scream out, depending on the people screaming not being on the other side of the planet for the hit.

They drawing they showed... well, it looked to be around the size of Mars.

 

[Carlobrand]

Clearly the momentum would be denied by the mechanical properties of stone and magma because it was. Again, the Chicxulub impactor had 20 times that momentum and it was stopped (in fact it appears from what I've read that the estimated depth of the crater was 30 km which probably did not even breach the crust). ...

Ummm, no, it would not be denied. We're not talking about the Chicxulub impactor. We're taling about:

... a ship travelling at a large fraction of the speed of light ...

Here's an interesting bit. A fastball packs about 130-140 joules. A .22 Short round packs about 110-120 joules, if the Wiki entry is correct.

https://en.wikipedia.org/wiki/.22_Short

Baseball comes in around 145 grams while the .22 is less than 2 grams. .22 short's a very light round, weak, but it's the .22 that will penetrate muscle, not the baseball. They don't interact with the body in the same way.

You are, in essence, comparing getting hit by a baseball with getting hit by a bullet. Chicxulub was perhaps 12-15 kilometers in diameter, delivered between 1 and 5 x 10²³ Joules. For math purposes, I'll use these figures.

http://impact.ese.ic.ac.uk/ImpactEffects/Chicxulub.html

You said 20 times, so let's use that. Our comparison c impactor delivers 2.5 x 10²² Joules. Say it's a scout/courier 100 dT, mass about 1000 metric tons. Velocity is about 223,600 kps, about 0.75 c.

Okay, now we have a meteor 15 km in diameter - 176.7 million square meters cross sectional area - impacting at 20 kps. We're comparing it to the scout: 24 meters wide, 7.5 meters tall, 90 square meter cross sectional area given that diamond shape, 223,600 kps.

Seriously, you're comparing a baseball with a bullet.

 

[esampson]

Ummm, no, it would not be denied. We're not talking about the Chicxulub impactor. We're taling about. . .

I think you and I have very different definitions of 'denied'. Sure, it made a crater but it failed to punch through. In terms of the scale of the planet it did nothing. If you shrunk the Earth to a ball the size that you could hold in your hand you probably wouldn't be able to feel a 30 km deep crater.

Here's an interesting bit. A fastball packs about 130-140 joules. A .22 Short round packs about 110-120 joules, if the Wiki entry is correct.

https://en.wikipedia.org/wiki/.22_Short

Baseball comes in around 145 grams while the .22 is less than 2 grams. .22 short's a very light round, weak, but it's the .22 that will penetrate muscle, not the baseball. They don't interact with the body in the same way.

You are, in essence, comparing getting hit by a baseball with getting hit by a bullet. Chicxulub was perhaps 12-15 kilometers in diameter, delivered between 1 and 5 x 10²³ Joules. For math purposes, I'll use these figures.

http://impact.ese.ic.ac.uk/ImpactEffects/Chicxulub.html

You said 20 times, so let's use that. Our comparison c impactor delivers 2.5 x 10²² Joules. Say it's a scout/courier 100 dT, mass about 1000 metric tons. Velocity is about 223,600 kps, about 0.75 c.

Okay, now we have a meteor 15 km in diameter - 176.7 million square meters cross sectional area - impacting at 20 kps. We're comparing it to the scout: 24 meters wide, 7.5 meters tall, 90 square meter cross sectional area given that diamond shape, 223,600 kps.

Seriously, you're comparing a baseball with a bullet.

In my example I was using a scout ship travelling at .5c. Let's stay with one set of numbers for now. Mass is also a bit under 800 metric tons. I already provided that.

Sure, a bullet and a fastball have the same amount of energy. You do realize that a major league fastball can kill a person and a .22 short round is easily survivable, right? They may not interact with a body the same way but they actually don't interact as differently as you might want to think. The baseball isn't going to penetrate muscle but it can definitely shatter a skull.

That's not what you've got though. You've got a fastball and something that is travelling faster but with 1/20^th of the energy of the fastball. It's more like a fastball and a high speed grain of sand. Now which one is going to do more damage?

Also, and this goes back to the issue of the airburst, a thrown baseball will penetrate a great deal more water than a rifle bullet with a much higher amount of energy. This is because as an object passes through a fluid (whether water or air) the force that pushes back against it is based on the square of its speed. While the baseball has a larger cross-section it still has far less force acting to retard its forward motion and so continues forward while the rifle bullet is actually destroyed by the impact with the water and stopped almost instantly.

Now again, I'm not saying that I'm absolutely certain this would happen. I'm also not saying that the airburst would result in no damage being done to the ground. I should have been clear on that. The airburst 30 km above the ground is still calculated to destroy buildings for hundreds of kilometers around the epicenter. This would be something like the Tunguska event on steroids. However, it would not result in a massive crater (assuming the airburst were to happen).

 

[Carlobrand]

In my example I was using a scout ship travelling at .5c. Let's stay with one set of numbers for now.

I did. 1/20 the cited energy for Chicxulub, 5 x 10²³ Joules, gave the numbers I provided, not the numbers you provided. 1/20 the lower value gave 1 x 10²². 800 metric tons at 0.5c yielded 9 x 10²¹ joules. But, given the magnitudes involved, a quibble.

...Sure, a bullet and a fastball have the same amount of energy. You do realize that a major league fastball can kill a person and a .22 short round is easily survivable, right? ...

Yup, the baseball could fracture your skull, stop your heart - but I'm reasonably sure you understood the analogy and are not trying to say the planet behaves like a human body. So, again, quibble.

...That's not what you've got though. You've got a fastball and something that is travelling faster but with 1/20^th of the energy of the fastball. It's more like a fastball and a high speed grain of sand. Now which one is going to do more damage?...

Interesting question. How much damage will a grain of sand do if it were fired from a particle accelerator that could shoot grains of sand? Because, really, that's what we're looking at here.

...Also, and this goes back to the issue of the airburst, a thrown baseball will penetrate a great deal more water than a rifle bullet with a much higher amount of energy. This is because as an object passes through a fluid (whether water or air) the force that pushes back against it is based on the square of its speed. While the baseball has a larger cross-section it still has far less force acting to retard its forward motion and so continues forward while the rifle bullet is actually destroyed by the impact with the water and stopped almost instantly. ...

Ah, so the ball subject to mechanical forces penetrates deeper than the bullet subject to mechanical forces. But, again, we're dealing with that grain of sand fired from a particle accelerator.

...Now again, I'm not saying that I'm absolutely certain this would happen. I'm also not saying that the airburst would result in no damage being done to the ground. I should have been clear on that. The airburst 30 km above the ground is still calculated to destroy buildings for hundreds of kilometers around the epicenter. This would be something like the Tunguska event on steroids. However, it would not result in a massive crater (assuming the airburst were to happen).

I'm not suggesting a massive crater either. Again, grain of sand fired from a particle accelerator. In - through - maybe out, but my knowledge fails once it starts interacting with the crust and lithosphere. I'd suggested a bullet through an apple once, but there's a scale problem that gives a more violent picture than I'm trying to portray. This is more like that 0.5c grain of sand fired through an apple. That scout has a 90 square meter cross sectional area that it's driving the energy through. Certainly as it encounters matter and reacts to impact with air, that cross section is going to change, but at 0.5 c it goes from Karman Line to impact in 6.67 x 10^-4 of a second. My thought is it spends the bulk of its energy within the planet.

What happens with the atmosphere, that's another story. If a lot of energy gets transferred to that column of atmosphere, it's going to be rather like a nuke went off. I'm getting something like 900 metric tons mass of air in a column 90 square meters in cross section, ground to space. 3/4 of that is in the bottom 11 kilometers. Physics-wise, what happens when an 800 ton solid mass at 0.5c interacts with a 333 ton 89 kilometer tall column of "trace" to "very thin" air? What happens when an 800 ton solid mass at 0.5c interacts with a 667 ton 11 kilometer tall column of air? Does the scout's configuration make the slightest difference? If we call the hull iron, then at 0.5c the atoms in the air are encountering impact energies at 6.5 GeV, if I have the math right.