Jump Bubbles

[Meanderer]

Missiles at speed can't be used against a planet either. They will burn up.

Absolutely correct statement, but I would clarify that to be missiles at extreme speed - Normal missiles - cannot be used normally. If you are looking at a typical explosive warhead, the heat and pressure will most likely tear the missile apart and may detonate it prematurely.

But you can check my math in terms of evaluating the energy. A 10 kg projectile travelling at 500 km/s will deliver the kinetic equivalent of 600 kilotons of TNT. The scale of this is horrific. The bomb dropped on Hiroshima in World War II had a yield of 16 kilotons. You have a weapon potentially launchable from any starship turret missile launcher that can deliver such an attack. Even if it is destroyed in the atmosphere, that energy is going somewhere. You can end up with something like the Tunguska event http://en.wikipedia.org/wiki/Tunguska_event. Smaller if you have just one missile. But if half of that spread of 1,440 missiles I mentioned weren't diverted from the planet we could be dealing with a combined force of 420 megatons. Keep in mind when reading about the destruction at Tunguska that the object that caused the destruction did not survive collision with the atmosphere (it exploded before it hit the surface).

Think of a cruiser squadron delivering the explosive effect of the entire nuclear arsenal of the USA. And, because this is purely kinetic energy no nuclear dampers will help defend against it.

I mentioned normal missiles. Missiles intended for such an attack may be specially built around a single shaft of hard metal. Such weapons were described in the Night's Dawn trilogy as being pretty much a spear of tungsten. (For Traveller: crystaliron perhaps; with Imperial navy loads using bonded superdense).

The concept is well known and the military application of this in a space-based weapon (Project Thor) is under development as a conventional weapon useful for penetrating and destroying deeply buried bunkers. http://en.wikipedia.org/wiki/Kinetic_bombardment.

An orbital based kinetic telephone pole made of tungsten apparently isn't considered a weapon of mass distruction. A missile heading at a planet at 500 km/s is nothing but a WMD. Seems like something there would be treaties against - though how good the treaty is depends on how much a government needs the other party to follow it. (Ink on a page). Scary stuff.

(From reference material I have, a 5 kg kinetic missile 60 cm long would be about 3 cm in diameter. This would be 300 kilotons at 500 km/s but (being about 2 feet long) should fit in a ship based missile. Thinking a missile a meter long would need some sort of special launcher. We could do some math on a kinetic kill torpedo (maybe it splits off into multiple spears of 3 m length or more. Mass is a straight multiplier. A 40 kg spear would have the kinetic energy equivalent of 2.4 megatons and it isn't much of a stretch to imagine a torpedo carrying 20 of them. )

 

[Meanderer]

Just a comment here. Science fiction is, at it's heart, an exercise of "What if?".

The tremendous threat of such attacks would be bound to influence defense, but the cost increases the further out you layer your defense. I don't think static defense sattelites make any sense except in close orbit. If you want to put a defense layer out 200,000 km out from the world it would be starships or system defense boats of varying sizes that can move and concentrate where they are needed.

Going back to jump drives, the +/- 15 hour time lag is useful in protecting against these attacks. Vessels jumping in cannot plan to emerge just 100 D out from the target world. Since the world is in motion (orbiting around its star) arriving early or late puts you on the wrong attack vector. You could plan a general vector to bring you in on an attack like this but would have to emerge a considerable distance back from the target world and overtake it in its orbit. Gives a lot of time for the system defense boats to get into position.

But the implications for defense means a lot of concentrated forces near the primary world which means less can be stationed out to defend the gas giant. A fleet could send a lone cruiser in every few days to do an attack run on the primary world - to draw back forces from outer parts of the system. As the SDB system takes a beating from these attacks they may have no choice even if they realize the intent is to weaken outer defenses.

Interested in everyone's thoughts on this.

 

[Wil Mireu]

But the implications for defense means a lot of concentrated forces near the primary world which means less can be stationed out to defend the gas giant. A fleet could send a lone cruiser in every few days to do an attack run on the primary world - to draw back forces from outer parts of the system. As the SDB system takes a beating from these attacks they may have no choice even if they realize the intent is to weaken outer defenses.

Interested in everyone's thoughts on this.

So don't defend anything else except the mainworld - the only border that matters is the one between the planet's atmosphere/Low Orbit and space anyway, the gas giant is irrelevant (unless it's the only source of hydrogen in the system, which is very unlikely). If anyone comes to attack the mainworld, it gets destroyed or repelled by the mainworld ships, which don't go out to chase it if it runs away. Eventually the mainworld can build up a fleet big enough to go to the GG and destroy/repel the ships that are out there.

 

[Meanderer]

Yeah, and the hit and run raids reinforce this. The invasion fleet will want to jump in somewhere in the outer system, and refuel at a gas giant. They will be vulnerable while refueling but with full tanks they have the option of jumping back out if the battle gets dicey.

But coming up with a perfect defense system is difficult. You can put a lot of defensive batteries including deep mounted meson guns to make it lethal to ships trying to come into orbit (or requiring all orbital bombardment ships to have heavy armor and cutting edge meson screens). But only major worlds can really put that much of an orbital defense up, but it is locked into position. A mobile force can draw out enemy forces and try for better position but if you are locked into defending the homeworld the enemy can sit back and whittle away at the defenses.

But then I think this is a large part of the binding force of the Imperium. Member worlds give up some sovereignty in exchange for a defense treaty. Holding the outer system and using it to launch long distance attacks on the major world will eventually force that world to capitulate, but if it takes long enough then imperial reinforcements may come to lift the siege.

[I have a correction to my TNT equivalents above. I grabbed the wrong amount of energy for a kilogram of TNT for a not so small error. I was off on an order of magnitude of 1000. So the 10kg missile would have the energy of 600 tons of TNT. So you need about 25-30 of them to equal the Hiroshima bomb. Sorry for the error.]

A friend suggested something worse than the missile attacks I described above though.

Take a spear of hard material. Crystaliron perhaps. Crystaliron being much harder and 1.25 times as dense as regular steel, you make it about 30 m long and 0.5 m in diameter, or about 57 tonnes of metal. Mounting this missile on a heavily armored 400 ton boat (like the SDB in the original Traveller supplement Traders and Gunboats) such that cumulative collisions with particles in space won't do to much damage to the boat. (A 400 ton starship capable of high acceleration is better because microjumps would be useful - see below)

From the outer system there is plenty of space to do a 2 billion km attack run, getting that kinetic spear up to a velocity of about 15,000 km per second (3 days of constant acceleration of 6G). Okay, maybe the physics of small collisions with dust particles (and even atoms of hydrogen) will take its toll on whatever is doing the accelerating even with lots of armor and with the weight of the spear only 5G acceleration is possible. Let's tone that down. Say just over one day of full acceleration getting up to 5,000 km per second.

Wondering what the kinetic energy is? You know it will be big. Sci-fi has lots of examples of near light speed objects used as kinetic missiles for planet busting impact. The good news is this kinetic spear isn't going to bust open the planet. The bad news is:

57,000 kg at 5,000 km/s means 1.43 x 10^18 joules. Converting that to comparison with nuclear weapons for amount of energy, we are talking about 340 megatons.

And remember we are talking about 57 tonnes of metal. The drives accelerating it are attached to a ship that lets the kinetic spear go and decelerates (maybe microjumping) away. You don't even need it to be precisely aimed. Say have a few dozen small starships do attack runs with these and you can launch a volley every week or so (say a week and a half if the ships are microjumping away). If you go with 30 such attack vessels you get ten gigatons every week and a half until they run out of these missiles.


If you are curious, if that spear could be brought up to 15,000 km/second the energy increases to 3 gigatons per missile. If you can launch a thousand such missiles at a time, that's 3 teratons equivalent. Not as dramatic as an extinction event like the Chicxulub impact believed to have killed off the dinosaurs - just 3% of that. If the objective is to induce nuclear winter, strategic modeling suggests this scale of strikes would still be overkill. http://en.wikipedia.org/wiki/Nuclear_winter

But that seems to be the nature of future war. As technology progresses our ability to destroy becomes so great that the thought of getting into a fight seems insane. Going up against an opponent armed with an assault rifle, sure. But a fusion gun (where a near miss can also be a kill even if you are in full armor)?

Intercepting a regular ship or missile going 500 km/s seems feasible but what about ten times that, or more? And what do you intercept 57 tonnes of metal with? Hit it with lasers? That will heat it up. But that really doesn't help. Destroying a chunk of solid metal seems difficult, and deflecting it will require a lot of kinetic energy.

The scary thing is that the big crystaliron spear I described is something easily done at TL 12 and could potentially be done by an adventuring group. (what does a 57 ton cylinder of hull metal cost?) I had been putting this in terms of a well-planned attack carried out by a major government. Now I am realizing that a terrorist group could do some serious damage.

Okay, a nuclear missile would be used to intercept it. Maybe a few such missiles because a guaranteed hit is needed. That's trading tactical nuclear missiles for chunks of metal. Interstellar war seems scarier and scarier. And that's if you see it coming. It has no emissions. It can be detected but with enough notice?

 

[sideranautae]

From the outer system there is plenty of space to do a 2 billion km attack run, getting that kinetic spear up to a velocity of about 15,000 km per second (3 days of constant acceleration of 6G). Okay, maybe the physics of small collisions with dust particles (and even atoms of hydrogen) will take its toll on whatever is doing the accelerating even with lots of armor and with the weight of the spear only 5G acceleration is possible. Let's tone that down. Say just over one day of full acceleration getting up to 5,000 km per second.

One nuc detonated on the "spear" and it is vaporized. Too easy and not worth more than moments thought by the defenders. In fact a couple B-lasers would do the same. As individual molecules, they are absorbed by the planets atmosphere. 8)