Dan Clemmensen wrote:
> You are correct in that I didn't run the numbers. I'm simply assuming that
> I can find 2 million comets with an aggregate mass of two eath masses, and
> that if I am willing to use fusion-powered ion engines, I can expend half
> the mass of each comet to direct the other half into the same converging
> hyperbolic orbit with very low relative velocities. Since each of the
> mass drivers is "small", far away, and directing its energy away from
> I assumed that detection from earth was difficult. As it happens, there
> are a few minor trivial loose ends on this hare-brained scheme. In
> I'm not quite sure how to manage the heat generated as the pieces
> into a single mass.
To do this you nead to move each comet a long way - about 0.1 LY, if I remember right. Ion drives at .01 G will take around 20 years, which is long enough to make the whole scheme irrelevant. To do it fast enough to matter you need to apply a velocity change of several thousand KPS in a space of a year or less. The exhaust is going to have to be extremely hot (otherwise you expend all your mass as fuel), and the drive system will also have a huge IR signature. It won't be visible to the naked eye from Earth, but it will certainly be obvious to even a modest-size early warning system.
> Please note that I don't feel that this is the easiest way to use nanotech
> to destroy a human-based civilization. I feel that direct application of
> military nanotech gives an overwhelming advantage to the attacker. My
> earth-mass impactor simply makes the attacker's advantage more obvious.
It always looks like the attacker has an overwhelming advantage if you gloss over the details. Using giant space-based weapons strengthens this effect because it moves you into an unfamiliar realm where the problems aren't obvious. That doesn't many anything has actually changed - its just that the 'gosh-wow' factor of schemes like this tends to cover up the vulnerabilities.
> Just for fun, let's try an earth-based approach. I think your nano-based
> defense model pits the defending naites against the attackers directly?
> That is, you need to know that an attack is occurring.
> What if I use my attackers to build hundreds or thousands of mega-nukes
> at an appropriate depth in the earth's crust? I don't have to burrow the
> nukes, I just program the seed nanites to first burrow and then build
> You cannot defend against this unless you are continuously monitoring the
> entire target volume: IMO this defense will require an SI.
A seed nanite can't build a nuke. You have to import plutonium, tritium, and other exotic elements, and export a lot of useless matter (probably several hundred cubic yards for a mega-nuke). You also need an energy source, which means running a power line to the surface and putting a visible power station there. You also need to figure out how to build such a device in the first place, and find a source for the raw materials. The appropriate depth to place them is less than a mile down, so you also have to avoid notice from all the other construction projects - if you can do this, others will be digging underground freeways, factories, bomb shelters, and who knows what else.
Now you're talking about something similar to the modern problem of terrorist nukes. It is possible (in theory) to pull of the project, but in practice it takes more knowledge, planning and organization that can be mustered by anyone who would want to do it. In the long run it might happen anyway - but I've already said I think we should migrate into space at the first opportunity.
Billy Brown, MCSE+I