Early missile defense system concepts were nuclear, because it was assumed that was the only way to ensure that a payload delivered to the right neighborhood would take out the missile. This would have resulted in so much collateral damage that it was abandoned early on, and gave a bad name to the concept of defense against missiles per se.

Thus, it was a breakthrough in missile defense when we developed (and continue to improve) the capability to guide projectiles with precision. This allows us to not only not use nuclear explosions, but to get away without using explosives at all. The high speed of the interceptor provides it with sufficient kinetic energy to kill the target from the collision alone.

This has apparently had a nice spinoff for a war in which we're trying to minimize collateral damage. I don't know if we're doing this, but the Brits have come up with a bomb with no explosives. It's basically just a thousand pounds of concrete which, when dropped from a height to a precise target (using the same smart guidance techniques as more conventional munitions), can do a lot of damage, but without having to explode. It's like something that ACME might manufacture, except it really really works.

The terminal velocity on one of these things would be several hundred miles per hour, I'd guess, given the density. I wouldn't want to be in a tank in a narrow city street when one of these things falls on it, but it's quite possible that one could be standing next to it when it occurred, and not be injured, or even have overpressure on the eardrums. But you definitely don't want to try to fair catch it.

Saves money, saves lives. Cool.

So we may be able to use such weapons quite surgically, even within a city. We may find out in the next few hours.

I seem to recall the USAF using something similiar in the former 'no-fly' zones. Iraq would park radar van for the SAM missiles next to houses, etc. Hitting them with a laser guided ton of concrete wrecked the target but tended not to injury too many bystanders. Good PR move. :)

I did a little fiddling with a spreadsheet- for a one ton projectile, density 3x that of water, 14" diameter and 140" long, with a drag coefficient of 0.2, the terminal velocity would be over 900 m/s. Since it isn't being dropped from over 50 km altitude, it *won't* reach that speed- but at a much more reasonable 400 m/s, (about 8000 meters in freefall), the kinetic energy is about 85 MJ- as much energy as 20 kg of TNT.

The flying fragments would still be bad for flowers and other living things, but with only a few percent of the energy of an explosive bomb, it certainly would be much less hazardous for the poor suckers the bad guys are hiding near.

A nice chunk of hardened steel would make a much better dart, would shed fewer fragments, and would likely nail the damn tank to the ground if nothing else...

Grizz

Funny you should say that--it's not all that new of a concept. Didn't any of you read The Moon Is A Harsh Mistress? "Loonies threaten to throw rice!"

Wasn't there something from SDI that described what was essentially long iron rods with some control surfaces at one end, in orbit, that could be brought out of orbit and used as a weapon?

"A nice chunk of hardened steel..."

You mean like a really big anvil?

"The Moon is A Harsh Mistress" is one of the first references to orbital kinetic weapons. "Footfall" by Larry Niven and Jerry Pournelle also has a solid mention, actually referring to it as 'Thor' which was the Pentagon's phrase for it when it was considered. The only thing keeping us from deploying these as space-based weapons are a couple of treaties signed with the defunct USSR, as the engineering involved is pretty much 1960's level, not state-of-the-art. Imagine the 'shock and awe' the beginning of the war would have had if we had hit the same targets simultaneously with nary a plane in the air.

Concrete bomb (Voice of America transcript at FAS.org).

Grizz, you're my kind of guy. ;)

I'd be extremely surprised to see terminal velocity on the "concrete bomb" reach more than Mach 0.8 or so: drag divergence tends to happen abruptly in the transonic regime, with large final Cd. I'd expect a maximum terminal velocity for something of that fineness ratio to be around 270 m/s, even with active controls to prevent the bomb from spinning.

I can say this with some certainty, because I've personally worked with low-Cd vehicles in that weight range, autopilot-controlled for spin, and we were unable to reach Mach 0.8 on a gravity drop. It wasn't from lack of trying...

Thomas,

I think you're thinking of Project Thor. Jerry Pournelle has some stuff about it at his website, http://www.jerrypournelle.com

With regard to a neat fictional treatment of precision guided, non-explosive weapons, be sure to check out Marc Stiegler's novel David's Sling. It also contains some fine insights about decision making and the proper training for decision makers.

Project Thor. That sounds like what I remember. Just cracked open Footfall. It's an interesting read, so far.

Am I the only one who immediately thought about bomber pilot Wile E. Coyote dropping a piano on Saddam from 40,000 feet?

The trick is to precision guide the piano to keep the angle as such to minimize coefficient of drag.

Wouldn't that be a great psychological tactic, though? Kill Saddam with a piano! Who would dare oppose us after accomplishing something as cool as that? ;)