(Captain's log): Geoff writes:
Having reflected on your possible outcomes wrt North Korea, it strikes me that what the US really needs is an effective massive non-nuclear attack capability which does not involve large numbers of personnel, such as THOR, sometimes known as 'smart rocks' or 'brilliant pebbles'.
All the power of a nuclear weapon without the fallout; described (by Jerry Pournelle) as a 'tungsten telephone pole' failing from orbit at 12,000 mph. No warhead or explosive necessary, the message is the medium or vice versa.Unfortunately, Thor, Thoth and High Sierra never saw the light of day.
There are a lot of ideas which look really nifty from a distance but turn out to suck the closer you look at them. There may well be a place for that kind of weapon, but not as a means of delivering massive devastation.
That kind of weapon can conceivably be really good at destroying specific targets, especially if the targeting can be made sufficiently precise (up to the standards of the other "precision guided munitions" we have), but it isn't a "massive attack capability". The energy causing the destruction is entirely kinetic energy converted from energy of position, and that means that energy has to be expended to lift all that mass into space.
In the book "The Moon is a Harsh Mistress", Heinlein talks about the process that the computer "Mike" uses to conclude that Luna Free State could use kinetic weapons to attack the Earth during its revolutionary war. In there, Heinlein buries a lot of key wisdom, and one observation is that all weapons are engines for manipulating and applying energy. That's even somewhat true for swords and bows, but is particularly true for pretty much any weapon developed for modern warfare in the last five hundred years. The primary purpose of any weapon is to apply energy to a target so as to cause some sort of damage or destruction, and if it does so extremely inefficiently it's probably not a very good weapon.
It's plausible that kinetic weapons could be used for certain kinds of attacks, but not for any kind of massive attack. The capability does not exist to lift that much stuff into space even at sub-orbital speeds. In Heinlein's book, the technology already existed to deliver bulk mass from Luna to Earth because it was being used to ship grain; Mike concluded that the same catapult could be used to deliver multi-ton payloads as a military weapon and would produce explosions at the level of a small nuke from the velocity of impact. Heinlein was careful in his construction of the scenario, and his physics was correct. But we Americans don't have a catapult on the Moon designed to deliver multi-ton payloads to Earth, and right now we don't even now how to build such a thing.
These things have to be evaluated on several different scales of efficiency. One is money: how much bang (or boom) for the buck, as it were. Another is time; how fast can it be done? Yet another form of efficiency would be energy: how much energy of various kinds, including fuel, do you have to use in order to accomplish the requisite destruction?
Cannons firing explosive rounds are pretty efficient. The cannon itself converts a good proportion of the power of the propellant charge into kinetic energy in the round. If the round being fired carries its own energy source (e.g. TNT) then the system is pretty energy efficient, with a pretty good percentage of the total energy expended causing useful destruction. (As it were.)
That became even better when ways were found to make the explosive rounds themselves more efficient (such as through the use of shaped charges). When we switched from the use of explosive rounds to kinetic penetrators for anti-tank rounds, it didn't actually degrade all that much. The energy all came from the propellant, but the large smooth-bore guns were still very good at utilizing it. (Relatively speaking.)
Cannons are also relatively cheap and the rounds are easy to produce in quantity, at a pretty low cost. So they're relatively efficient in money, in time, and in energy conversion.
As weapons of mass destruction, orbital or sub-orbital kinetic weapons fail all three tests. Per unit destruction they create, they would cost far too much, take far too long to develop and deploy, and waste far too much energy.
The current technology of space flight (rocket engines) is inherently wasteful. It takes a huge extremely expensive rocket loaded with immense amounts of fuel to boost a relatively small payload into orbit. Rocket engines are inefficient anyway, and most of the fuel in a rocket is consumed to lift the rocket or the fuel itself. If you calculate the energy efficiency as the energy in joules which a payload in orbit gained during launch and orbital insertion divided by the amount of energy inherent in the fuel (even ignoring the further energy which was expended to manufacture the rocket), you find that it's an appallingly low ratio when compared to such things as railroads or cargo ships. We rockets because right now we don't have any other technology which is better. But even a crummy solution is better than no solution at all, and just because you can't do something big doesn't mean it isn't worth doing.
The first person to figure out how to melt steel, and to produce steel which was reasonably consistent, could only produce batches of maybe fifty