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A collection of posts by David Weber containing background information for his stories, collected and generously made available Joe Buckley.

"Buckshot" missile defenses

In article <35703122.72506C49@mindspring.com>, Armorfiend writes:

I wasn't thinking you'd even be looking for it, though. In wartime, surround your bases with a bunch of this junk, and shoot out even more of it when you know an enemy fleet's passing through the system. An added bonus is that your radar sig would probably be increased 40 fold, confusing the missile's sensors...

Still there is a range where such a system would be effective. But even an Ensign on first deployment is unlikely to pick just that spot to shoot

Gorg

Okay, folks. I was gonna just let you make nice with each other, but Richard is back from "over there" and picking on me, so I looked through the thread. Here's the skinny (as I see it).

#1: Chuck is right that there is a very simple way for mobile forts to avoid c-frac bombardment; they move. Not sometimes; all the time, even when they're officially at "stand-by." And leave us not forget, in regard to that, that the wormhole (which is where the RMN has put most of its forts) is like ten light-hours from the nearest star and does not have either mass or a gravity well of its own. Hence there is no mass for an orbit to center on, which means the forts' drives have to be up, at least at station-keeping levels, just to stay in one place, which makes steady, slow, random movement the best (and cheapest) defense.

#2: The biggest problems with the "buckshot" are

(a) the sheer scale of the "cloud" required;
(b) the problems it creates for everything else in the vicinity;
(c) the fact that it works against one and only one form of attack.

Those who point out that success requires saturating a sphere 30,000 kilometers in diameter are precisely correct, and whatever the monetary expense of the operation (which, I am sure, would be huge), the sheer mass required would make it impractical. Space is big, people, and covering that much of it with sufficient density and particles of sufficient mass to do the job would require a simply enormous operation in materials handling. Nor would simple "replenishment" of portions of the cloud be a solution. Presumably you shoved all that stuff out there at some velocity, and it will keep right on moving at that velocity (relative to the station you're trying to protect, at any rate) until something stops it.

While ships are protected by their wedges and particle shields while underway, the same is not true of satellites, space stations, asteroid extraction processing stations, etc., etc. If you start filling large volume of space in your star system with "brilliant pebbles" (or their moronic cousins), there are lots and lots of things you can screw all to hell when they run into the defensive cloud.

Finally, this defense would work only against c-frac attacks. A missile under power would not be affected by it in any noticeable way, although it could certainly (if dense enough) screw up active seekers in terminal stage attacks. No navy could afford to make the investment in such an enormously costly passive defense when it would be used only against one form of attack, and that a form which is made relatively rarely.

#3: Lining up a "stealth" shot against a far distant, fixed target would not (I strongly suspect) be so easy as Chuck seems to expect. Even the teeny-tiniest error would generate an enormous miss at such long ranges, and any conceivable target (short of a moon or planet) is a very small mark to shoot at in deep-space terms. You would need incredibly detailed information and an absolutely accurate position fix for the launching platform to have any hope at all of hitting any artificial space structure which I can imagine (well, short of Dahak, and he ain't in this universe!)

#4: A "snapshot" barrage of counter missile down the threat axis upon notification from distant FTL-com-equipped sensor platforms would seem to me to be a better, more cost-effective solution to the problem than an immense cloud of buckshot. Your platform doesn't have to be able to give you absolutely detailed information on the incoming fire; all it has to do is scream: "something's coming from 123-degrees by 021-degrees! Halp!" with a time chop. At that point, you know the general bearing of the threat and your point defense computers can make a pretty good guess as to arrival times, so you begin firing blind at the earliest moment you calculations suggest a threat missile could be within countermissile range. You carefully space your shots down the known threat axis in order to sweep the maximum volume of space, and any c-frac bird in that volume is dead, because it will be eaten by the wedges of the counter missiles. You can stagger your launches to avoid wedge-induced fratricide amongst your counter missiles, because it doesn't matter precisely when a specific portion of the defended volume is swept. Anything headed through it will still be headed through it; all you have to do is catch it (a) before the drive on your counter missile burns out and (b) before the attacking missile reaches attack range (30,000 km). This defense would cost enormously more when you actually fire it, but enormously less in terms of long term maintenance. And in the case of orbital forts in wartime, the anti-missile systems are always at stand-by under computer control, which takes a lot of the human reaction element out of the fire control loop for this scenario. Note also that in the case of fortress groups, like those on the Manticoran Wormhole Junction, forts whose systems are fully up would be responsible for protecting forts whose systems are on stand-by or stood fully down as well as themselves. Thus there would always be someone available to lay down defensive fire in such a case.

#5: Most c-frac attacks on targets in major systems will not be launched by someone you don't even know is there. There was a great deal of discussion in an earlier thread about the difficulties inherent in "sneaking up on" a star system with modern passive sensor arrays. That holds true for ships trying to get into range for a c-frac launch, as well. That means you will at least have a notion of where such an attack would be coming from, and, at the very least, would be able to vector your own mobile units out for a look see. In addition, you could (and no doubt would) reconfigure your available fixed sensor assets to look very closely at the potential threat axis, and if you have FTL capability, you're back into #4, above.

There are undoubtedly cases in which a "buckshot" defense would work. In HH's universe, however, those cases are such special ones that I don't see any modern navy making the investment in time and money. As someone said, this isn't a case of bankrupting yourself in order to put the defense in place; it's a case of bankrupting yourself and failing to put a defense in place and diverting so much time and effort to it that you leave yourself vulnerable to other, more "conventional" forms of attack.

#6: Ships do have particle shielding which operates against normal density particles. Missiles do also, at least while their drives are up, although their particle shielding is less impressive because they are normally not going to need it for as long. When a missile's wedge goes down, however, so does its particle shielding. If the shielding were up, it would require quite a heavy particle (relatively speaking) to do the job; once the wedge is down (as in our classic-profile c-frac attack), missile particle shielding would become a moot point.

There. I'm done. And I'm going back into lurk, Richard. Leave me alone. I'm not coming out again. And if it should happen that I do come back out, somebody is getting a red shirt. Again.

David