Interstellar War

[Codraroll]

Wouldn't you be able to see a kinetic kill vehicle coming literally years in advance, relativistic or not? Stealth in space is pretty impossible, after all. In a wartime scenario with that sort of technology, any large object being accelerated in the other system would be picked up by enemy sensors before it even reached orbital velocities. Ample time to set up several layers of defense and intercept. Given a large enough laser (or even a lens) stationed in the right spot, one could nudge the kill vehicle a few millonths of a degree off-course, causing it to miss by several AU.

Or of course, there's an ultimate counter to kinetic weaponry: Be somewhere else when it hits. Again, stealth in space is impossible and you get ample warning time. Moving planets out of the way may not be feasible, but space stations could be moved on relatively short notice. It's not like the enemy could issue commands to correct the course, given that they would observe any movements four years after they happen.

 

Anyway, I have a feeling that this whole discussion is akin to medieval knights discussing details of future jousting, with horses that go a hundred miles per hour and saddles that can keep any knight mounted no matter what. By the time the techniques discussed are even feasible, the larger picture is so irrelevant it's laughable.

[p1t1o]

9 hours ago, Codraroll said:

Wouldn't you be able to see a kinetic kill vehicle coming literally years in advance, relativistic or not? Stealth in space is pretty impossible, after all. In a wartime scenario with that sort of technology, any large object being accelerated in the other system would be picked up by enemy sensors before it even reached orbital velocities. Ample time to set up several layers of defense and intercept. Given a large enough laser (or even a lens) stationed in the right spot, one could nudge the kill vehicle a few millonths of a degree off-course, causing it to miss by several AU.

Or of course, there's an ultimate counter to kinetic weaponry: Be somewhere else when it hits. Again, stealth in space is impossible and you get ample warning time. Moving planets out of the way may not be feasible, but space stations could be moved on relatively short notice. It's not like the enemy could issue commands to correct the course, given that they would observe any movements four years after they happen.

 

Anyway, I have a feeling that this whole discussion is akin to medieval knights discussing details of future jousting, with horses that go a hundred miles per hour and saddles that can keep any knight mounted no matter what. By the time the techniques discussed are even feasible, the larger picture is so irrelevant it's laughable.

Relativistic Kinetic weapons are usually defined as travelling fast enough that it arrives at its target only shortly after any possible observation of its departure via light. Its about the only stealth that works.

[kerbiloid]

10 hours ago, Codraroll said:

Wouldn't you be able to see a kinetic kill vehicle coming literally years in advance, relativistic or not?

Say, we now see that Centauri launched something big and ugly-looking in this direction. ETA 10 years.
Looks like we could undertake some countermeasures only if already had reached at least their technical level.

Multiple relativistic rods probably could be stopped by a dust or plasma cloud appearing on their way, making them vaporize.
But this also would require a big antimatter charge and a sacrificial asteroid.

Probably, this is the fork critical for relativistic kinetics:
If it's too large, we can send one accurate probe (or a pack of them) and hit it with one hit.
If they are small and numerous, we can't hit them personally, but any particle of sand hits them as a projectile making to vapourize.
So, the negotiation is about some intermediate projectile size when there can be many of them at once, but enough bulky to run through a dust cloud.
In any case, both cloud and interceptor need the technological level comparable to the agressor's one.

Edited February 22, 2017 by kerbiloid

[magnemoe]

16 hours ago, p1t1o said:

 

The only defence against a RKV is to pre-emptively exterminate any civilisation which has the capability to build one.

Greg Bears "Anvil of the stars"/"Forge of God" book pair dedals with this concept, although with a slightly different weapon (Von Neumann weapons).

As in, as soon as you get word that the folks at Alpha Centauri have the technology to launch an RKV, let alone build one, you launch yours. Its the only way to guarantee survival, boiling it down to an arms race.

Downside - your action will be visible for light years, advertising yourself as someone very much worth exterminating (not only do you prove you have RKV capability, you prove you have the will to actually use it).

So the other option is civilisational stealth, which as you can imagine, has its problems.

Problem with RKV is that they don't work well against smaller movable installations. Anybody who colonize another star with plausible technology will have significant space infrastructure 
An good estimate is that the ship will use more energy than the energy earth receive from the sun. 

An decent chance that killing the planet will kill 90% of the population but only 10% of the industrial capacity, the spare industrial capacity will be used by the military or to expand industry for later military use 
 

1 hour ago, p1t1o said:

Relativistic Kinetic weapons are usually defined as travelling fast enough that it arrives at its target only shortly after any possible observation of its departure via light. Its about the only stealth that works.

Yes, however .99 c is pretty unrealistic, 

[p1t1o]

1 hour ago, magnemoe said:

Yes, however .99 c is pretty unrealistic, 

We ARE talking *interstellar* war here...  It presumes levels of technology, and economy (possibly more important) that make these things far more plausible.

If it takes 3 centuries for your weapons to travel the distance, the war is not really a war is it. High relativistic travel is almost assumed as a given.

 

Edited February 22, 2017 by p1t1o

[magnemoe]

2 minutes ago, p1t1o said:

We ARE talking *interstellar* war here...  It presumes levels of technology, and economy (possibly more important) that make these things far more plausible.

If it takes 3 centuries for your weapons to travel the distance, the war is not really a war is it. High relativistic travel is almost assumed as a given.

Not centuries, I assume pretty high speeds here 0.5 c or higher, however 0.9 c and faster is hard. Forget beamed power because of the red shift. Even an staged very good anti matter rocket will have limits.
Going fast enough even an reactionless drive powered by an fusion engine is limited by the energy in the fusion process. 
 

[kerbiloid]

If look into perspective, a permanent birth/annihilation of vrtual particle pairs can give you energy if separate them in proper way. Just an antimatter appearing from nothing.
Also this could power an Alcubierre drive and probably provide with some kind of antimatter. So, you get at once a hyperdrive and a rocket engine.

[p1t1o]

1 hour ago, magnemoe said:

Not centuries, I assume pretty high speeds here 0.5 c or higher, however 0.9 c and faster is hard. Forget beamed power because of the red shift. Even an staged very good anti matter rocket will have limits.
Going fast enough even an reactionless drive powered by an fusion engine is limited by the energy in the fusion process. 
 

Can you fight an interstellar war with a minimum 8 year travel time (for alpha centauri which I assume we are all basing this on)? Theres quite a risk that peace might be achieved whilst your planet killer is still on the way. Or *theirs*.

*Why* you would fight such an expensive war with someone so far (in time) removed from your society is a discussion for another thread, but helps to form the assumed technological environment.

Even so, cutting warning time in half would still be a highly significant military advantage.

Edited February 22, 2017 by p1t1o

[kerbiloid]

3 minutes ago, p1t1o said:

Theres quite a risk that peace might be achieved whilst your planet killer is still on the way.

To achieve peace, they need to communicate. How can they talk with Centaurian savages faster than with the ship which is still on its way?

[p1t1o]

13 minutes ago, kerbiloid said:

To achieve peace, they need to communicate. How can they talk with Centaurian savages faster than with the ship which is still on its way?

It might not be a ship, could just be a rock.

Also, people on strategic mass-destruction missions are likely going to be trained very hard to ignore messages from the enemy whilst en-route.

[kerbiloid]

2 hours ago, p1t1o said:

Also, people on strategic mass-destruction missions are likely going to be trained very hard to ignore messages from the enemy whilst en-route.

Then they should send to the captain a genealogical tree of his hamster or another secret info.
And let them have a reserve copy of CRM-114 discriminator.

[0111narwhalz]

2 hours ago, kerbiloid said:

If look into perspective, a permanent birth/annihilation of vrtual particle pairs can give you energy if separate them in proper way. Just an antimatter appearing from nothing.
Also this could power an Alcubierre drive and probably provide with some kind of antimatter. So, you get at once a hyperdrive and a rocket engine.

I think it takes more energy than it produces to separate the pairs.

[kerbiloid]

2 minutes ago, 0111narwhalz said:

I think it takes more energy than it produces to separate the pairs.

They born separated. Just don't let them to stick back.

[0111narwhalz]

15 minutes ago, kerbiloid said:

They born separated. Just don't let them to stick back.

That's like the classic "door compresser," where you concentrate a gas on one side of the door by just opening and closing it at the appropriate time. The sensing of the position of the particles wastes any energy that could be gained by producing the gradient.

In other words, thermodynamics.

[kerbiloid]

3 minutes ago, 0111narwhalz said:

In other words, thermodynamics.

Just    make their retrograde quantum state impossible, and their wave function will do all other job.

[0111narwhalz]

3 minutes ago, kerbiloid said:

Just    make their retrograde quantum state impossible, and their wave function will do all other job.

That sounds like it takes energy.

[kerbiloid]

Just now, 0111narwhalz said:

That sounds like it takes energy.

Depleting potential energy of vacuum. We have many vacuum.

[0111narwhalz]

1 minute ago, kerbiloid said:

Depleting potential energy of vacuum. We have many vacuum.

Ahh. You are creating a gradient where there was none. That requires that you lose a little more of a gradient elsewhere.

[kerbiloid]

So, the target is at 40 light years from here...

[YNM]

It'd be fought very slowly. At first.

Soon, one of the early ship sent came to see a destroyed enemy. And destroyed homebase.

Case closed.