Relativistic Weapons

[Beastttt]

at what angle did you set it for
you get better craters if the angles is as close to 90 degrees as possible

Interesting. Not nearly as devastating as I'd thought, if I'm putting the right numbers in now and the program can make decent predictions based on such extremes. Pretty much a Tunguska event for any of the smaller starships* travelling at 0.5C with the atmosphere preventing much direct damage.

Either the whole C-rocks thing is after all a moot point (too little damage for the investment, at least for a world with a standard atmo) or we're gonna have to use a bigger ship

* I plugged in the 30m diameter Merc Cruiser with various densities.

 

[far-trader]

at what angle did you set it for
you get better craters if the angles is as close to 90 degrees as possible

Yep. I tried both 45 and 90. Since 45 seemed more realistic, and I knew 90 would be the best. It made no difference, both we disintegrated in the upper atmosphere. If I recall correctly.

 

[Beastttt]

if it is being done on purpose 90 degrees is what most villians would shoot for unless time was a factor

at what angle did you set it for
you get better craters if the angles is as close to 90 degrees as possible

Yep. I tried both 45 and 90. Since 45 seemed more realistic, and I knew 90 would be the best. It made no difference, both we disintegrated in the upper atmosphere. If I recall correctly.

 

[far-trader]

if it is being done on purpose 90 degrees is what most villians would shoot for...

Shoot for yes, hit... a little harder. Not that it would matter with a near-C impactor. They both seem to be planetary destroyers. Of course if you're going to allow it, why just send one, send a dozen, or twenty. One of them will have to hit at 90 degrees right.

If we're going to accept that such tactics and attacks are possible, probable, and even conducted I think we have to presume defenses have been implemented. Let's talk about that for a bit too?

 

[Beastttt]

sensors out among the asteroid belt(s)

have your own rocks to use as interceptors

posted speed limits near habital planets if exceeded reason to shoot if aimed at a world

colonies would need gaurding ships and orbital platforms

pretty much any colony will either be well gaurded or hidden somehow till defenses are built up

generally speaking any rock will be seen with plenty of time unless somebody is pushing at a target and them you will have a drive to target

sending a mining remote to bore a hole and have a cargo drone with a bigger than normal fusion warhead head in the bored hole to deliver it's cargo to shatter it from inside
all the while your gaurd ships fend of the rock herders

you also make it a war crime that is more like we will come and do the same to you policy or shoot you before we have the trial that you would have been hang at anyway

nearby colonies forming posses to track down the villians

considering that we right now can Id naval ships by their engines and prop
sensors of the future could easily do this also
then broad cast the info to hundreds of recorders that are seeded all over the system and all they do is listen and record
and when the navy makes it's bi-monthly visit should the colony be destroyed the navy ship can bring up it's partial list of locations for recorders(so if captured it cannot give away all the recorders locations)
go and retrive 1 for study and figure out who did this horrible act
and get word out to hunt them down

having X-boats outside the 100 diameter limits ready to emergency jump should they get a signal or an unauthorized ship gets into extreme firing range maybe even have a weapons platform to guard it and the X-boat sits inside it

jamming will be next to usless with the recievers having directional antennas you will need to be in line between the sender and reciever
and the sender can send omni directionaly to not give the recorders position away

about the only way to do a rock throw would be to have a large freighter loaded with rocks come in looking like they are going into orbit to land and drop them then with maybe 1 or 2 turns of accelleration real close to the planet or dive in itself either way it would be a suicide mission

 

[Jeff Hopper]

Thanks for the calculator, it'll be great for when I throw rocks at worlds!

But it really doesn't look like it was designed to handle Near-C impacts. One of the things that I'm assuming will happen when the impact occurs is a radiation wave directly proceeding the wave of plasma created by the kinetic energy of the impactor hitting any matter.

Even if you have a small, under one-ton, impactor hitting a world I think the effects could detsroy the world's biosphere from shockwave induced seismic disturbances, nuclear winter style dust cloud, atmospheric overpressure and heating, and the exit hole that the impactor would create on the way out of the other side of the world.

 

[far-trader]

Thanks for the calculator, it'll be great for when I throw rocks at worlds!

You're welcome, I was hoping when I thought of it that it'd handle near-C but oh well. Imagination will have to fill in I guess

Yeah, I was wondering if it would include a hard nuclear blast. I think a near-C impactor is going to hit the upper atmo like a brick wall though, forget planetary impact by the primary mass. If there's anything left of it, it'll be a molten jet, perhaps mostly shooting back into space from the blast, but the blast effect alone will probably glass the world to the horizon, boiling off the water. The atmo will be blown off, taking the surface all the way around the other side with it in the process. The last thing anybody will be worrying about are the off the scale, mantle cracking earthquakes and super volcano eruptions. The world will be toast I think.

 

[EDG]

I'm trying to get my head around the numbers involved here in case they shed any light on the matter.

Of course, this is rather problematic because of how Traveller's design systems quantify manoeuvre drives - I only know of one (TNE's FF&S) that actually bothers to explicitly relate power and mass and thrust - the Mongoose one is unfortunately totally lacking in this sort of info. So I'll have to go with FF&S' assumptions jere.

In FF&S, each cubic metre of thruster plates generates 40 metric tons of thrust, weighs 2 tons, costs 1 MCr, and consumes 1MW of power. And the assumption in the book is that we need 10 tons of thrust per displacement ton (14 cubic metres) of spacecraft in order to accelerate it by 1G. So I guess the assumption there is that each dt of ship has a mass of 10 metric tons.

Now, by "ton of thrust" I guess they're really talking about a 'ton-force' which is 1000kg multiplied by 1G, or about 10,000 Newtons of force ( http://en.wikipedia.org/wiki/Kilogram-force ). So each cubic metre of thruster plate generates 400,000 N of thrust.

We can check this using Newton's second law (F=ma): 400,000 N will accelerate 40 tons (40,000 kg) of mass by 10 m/s, or about 1G. All good.

Now let's find a planetoid. Say we pick one that's 50m in diameter, and we'll settle for a spherical cometary body in the kuiper belt (it's ice, so density is 1000 kg/m3). So the mass of this body will be about 500,000 metric tons, and its volume is about 37400 dt.

So using F=ma again, we need a force of (500,000,000 * 10 =) 5 billion N to get this accelerating at 1G. That's 12,500 cubic metres of thruster plates, massing 25,000 tons, requiring 12.5GW of power and costing 12.5 GCr and taking up 2500 square metres of area (a 50x50 m square).


So far so good... but I can't help but feel that we're overlooking something here. The problem is that asteroids aren't stationary objects - they're orbiting the star. This means that they have velocity to start with, which also means that they have momentum. Let's say that out in the Kuiper belt (call it about 40 AU from the star), the orbital velocity of a planetoid is about 5 km/s - similar to Pluto. Momentum is equal to (mass * velocity), so our 50m radius iceball, with its mass of 500,000,000 kg, and going at 5000 m/s (funny how this is all fives!) has a momentum of 2.5e12 Newton seconds.

Unfortunately, here's where my understanding breaks down because I can't recall how to figure out how its initial momentum affects any attempt to change the velocity of the asteroid. This is possibly complicated by the fact that thrusters are reactionless drives, and so conservation of momentum kinda gets thrown out of the window. But qualitatively speaking at least my gut instinct is that the asteroid's orbital momentum (or possibly its inertia) has to be overcome before its velocity and acceleration vector can be changed to point toward the centre of the system (where the habitable target planet is), and that is probably going to be hard to do for a body of this mass travelling at 5 km/s. But I'll have to leave that to someone with a better understanding of mechanics than I have...

 

[Jeff Hopper]

Yeah, I was wondering if it would include a hard nuclear blast.

That is where my level of physics knowledge fails me. The numbers I'm crunching for the energy released at the point where a 0.8C+ impactor hits the atmosphere are so huge that they only make sense if the atmospheric elements themslves are breaking down. Not just chemically, because everything is reduced to its component elements from the energy released, but a handful of the gases (nitrogen, oxygen) look like they might undergo fission from the shock at the initial point of impact.

And that is just too weird for me.

 

[rust]

But qualitatively speaking at least my gut instinct is that the asteroid's orbital momentum (or possibly its inertia) has to be overcome before its velocity and acceleration vector can be changed to point toward the centre of the system (where the habitable target planet is), and that is probably going to be hard to do for a body of this mass travelling at 5 km/s.

Probably a silly question, but: Would the asteroid not move into a lower
orbit around the sun (= move inwards and closer to the center of the sy-
stem) automatically once it is decelerated ?

And while I am at silly questions: Could a (minor) impact create a vol-
canic "hot spot" on a planet, a small region where the planet's crust
has been weakened and a volcanoe could appear ?

Thank you !

 

[EDG]

Probably a silly question, but: Would the asteroid not move into a lower orbit around the sun (= move inwards and closer to the center of the system) automatically once it is decelerated ?

I think it would. Which is another reason why attaching a drive on an asteroid and accelerating it inward seems silly to me.

And while I am at silly questions: Could a (minor) impact create a vol-
canic "hot spot" on a planet, a small region where the planet's crust
has been weakened and a volcanoe could appear ?

Well the impact would melt some of the crust, and the crater itself could be filled with impact melt (or filled by eruptions from fissures if the crust within it is thinned enough, like on the Moon) but I don't think you'd be able to get random volcanoes sprouting up around the crater because of it.

 

[Infojunky]

And while I am at silly questions: Could a (minor) impact create a vol-
canic "hot spot" on a planet, a small region where the planet's crust
has been weakened and a volcano could appear ?

Long term or short term? I can see an one time event after the impact event as the fractures around the site fill from below.

But a lot of vulcanism it related to the sub-crust topology.

 

[rust]

I can see an one time event after the impact event as the fractures around the site fill from below.

Thank you, I think that one time event is all I need to justify a lava flow
leading away from the crater region - I would have disliked to have to
redraw the map.

 

[Infojunky]

I can see an one time event after the impact event as the fractures around the site fill from below.

Thank you, I think that one time event is all I need to justify a lava flow
leading away from the crater region - I would have disliked to have to
redraw the map.

Your welcome.

 

[Rikki Tikki Traveller]

I'm trying to get my head around the numbers involved here in case they shed any light on the matter.


(SNIP energy calculations)

Summary:
Asteroid Mass: 500KTons
Volume: 37.4KTons
Orbital Velocity: 5km/s

So far so good... but I can't help but feel that we're overlooking something here. The problem is that asteroids aren't stationary objects - they're orbiting the star. This means that they have velocity to start with, which also means that they have momentum. Let's say that out in the Kuiper belt (call it about 40 AU from the star), the orbital velocity of a planetoid is about 5 km/s - similar to Pluto. Momentum is equal to (mass * velocity), so our 50m radius iceball, with its mass of 500,000,000 kg, and going at 5000 m/s (funny how this is all fives!) has a momentum of 2.5e12 Newton seconds.

Unfortunately, here's where my understanding breaks down because I can't recall how to figure out how its initial momentum affects any attempt to change the velocity of the asteroid. This is possibly complicated by the fact that thrusters are reactionless drives, and so conservation of momentum kinda gets thrown out of the window. But qualitatively speaking at least my gut instinct is that the asteroid's orbital momentum (or possibly its inertia) has to be overcome before its velocity and acceleration vector can be changed to point toward the centre of the system (where the habitable target planet is), and that is probably going to be hard to do for a body of this mass travelling at 5 km/s. But I'll have to leave that to someone with a better understanding of mechanics than I have...

Well, it's been about 10 years since my Orbital Mechanics classes, but I should be able to help:

Since we are using reactionless thrusters, you don't have conservation of momentum, so you don't need to worry about it. Also, momentum would be important here if we had to worry about reaction mass for thrust, which we don't.

BUT, since the object is most likely orbiting in the same direction as the target planet, you will have to overcome that 5kps orbital speed as part of your calculations. Since we are going Near-C, you can probably not worry about that though. Assume 0.5c (150,000 kps) and that 5kps is negligible.

So, figuring Kinetic Energy directly is probably just fine.

When the object (solid or ice or rubble or whatever) hits the atmosphere, it will convert all of it's KE to heat and deformation of the atmosphere (wind) and planetary surface (crater). Some of that will leak back in to space, but most would be absorbed by the planet and atmosphere.

While it is possible that a SMALL fission process might take place, I don't have the formulas to crunch the actual temperatures to see if fission is possible, so lets assume it isn't.

All of this will happen within a fraction of a second.

I don't think even a 500Kton rock will be enough to extinguish life on a planet (the Dinosaur killer was what 10 km in diameter?). BUT, it would sure ruin a cities day and have devastating weather changes all over the planet.

Compared to the size of a PLANET, a 50m rock isn't all that big, but the velocity is what gets you. You could probably get the same effect by accelerating a ship (5000tons or so) to the same velocity and aiming it at a planet.

At 1g, it would take 177 days (25.3 weeks) to get to 0.5c.
It would have to travel approximately 7,650 AU.

So, while it is POSSIBLE, surely a few well placed Nukes would be cheaper, easier and faster.

 

[lastbesthope]

EDIT: To clarify, at the very least you'll get the entire kinetic energy of the impactor converted to heat (so that's 500 gigatons of TNT equivalent for our 200 ton ship travelling at 0.5c.

I'm sure at least some of the momentum would be transferred rather than converted into heat.

I mean how else can I play interplanetary pool?

:lol:

LBH

 

[EDG]

Since we are using reactionless thrusters, you don't have conservation of momentum, so you don't need to worry about it. Also, momentum would be important here if we had to worry about reaction mass for thrust, which we don't.

I wonder if there's some equivalent of reaction mass that we do have to worry about though. e.g. the energy you're putting into the drive has to be converted to kinetic energy?

BUT, since the object is most likely orbiting in the same direction as the target planet, you will have to overcome that 5kps orbital speed as part of your calculations. Since we are going Near-C, you can probably not worry about that though. Assume 0.5c (150,000 kps) and that 5kps is negligible.

Except that you don't go instantaneously from 5 km/s at a tangent to the orbit to an inwardly radial 0.5c vector. Sure, the rock might start accelerating at 1G in the radial direction but it'll still be moving at 5km/s on its orbit and you have to get rid of that lateral motion somehow.

I don't think even a 500Kton rock will be enough to extinguish life on a planet (the Dinosaur killer was what 10 km in diameter?). BUT, it would sure ruin a cities day and have devastating weather changes all over the planet.

Compared to the size of a PLANET, a 50m rock isn't all that big, but the velocity is what gets you. You could probably get the same effect by accelerating a ship (5000tons or so) to the same velocity and aiming it at a planet.

I think a 500 Gigaton explosion would have serious planetary-scale effects - it shouldn't really matter if that's caused by a slow 100 km diameter rock or a relativistic 50m radius rock.

At 1g, it would take 177 days (25.3 weeks) to get to 0.5c.
It would have to travel approximately 7,650 AU.

There is that too . though even after 40 AU of acceleration it'd still be going fast enough to cause some serious damage I think?

 

[Allensh]

Wow, Empty Hex Jumps, Jump Torps, and near-c rocks all showing up at the same time here... it's all the classic Traveller flame wars in one place! Who needs any other boards now...

Yes, all we need now are Aslan pirates in comfortable shoes and we'll be all set..

Allen

 

[far-trader]

Wow, Empty Hex Jumps, Jump Torps, and near-c rocks all showing up at the same time here... it's all the classic Traveller flame wars in one place! Who needs any other boards now...

Yes, all we need now are Aslan pirates in comfortable shoes and we'll be all set..

Allen

And it's all, always, new to somebody

I'm impressed at the relatively low thermodynamic properties of the topics here. So far at least. Nice to see.

 

[Beastttt]

here is a fun site I found on the Hero system boards
scroll down for the throwing rocks near c velocities

http://www.projectrho.com/rocket/rocket3x.html