Yes, folks, it’s that time again for the first time when I answer y’all’s background questions!

We have one question this month. James Sterrett asks:

What precursor elements do autofacs require for fabrication?  The same elements in the same proportions as the finished product (plus waste etc), or can they synthesize required elements?

Well, now, that’s an interesting question with quite a complicated answer, inasmuch as autofacs are rather complicated things in themselves..

Let me first suggest that this might be a good time to re-read Things That Make Things, since it covers a lot of the terminology I’m about to be throwing about.

So let’s start at the small end, with one of the most common working parts of an autofac, and which is also the core component of a cornucopia, including the ubiquitous desktop nanoforge, the portable nanolathe, and the specialized fabbers.

These, themselves, can’t synthesize elements, or indeed produce any other part of their feedstock – which is to say, you can’t just throw trash into them and have them rearrange it into what you want (you need specialized disassemblers for that, that are hardened to the job. Throw trash into a cornucopia, you have a good chance of wrecking the delicate internal components). They’re just glorified 3D printers. They’re absolutely dependent on a supply of feedstock, which is called nanoslurry.

(One exception to this is that you can also get what is called a nanobrick, which is basically dehydrated nanoslurry and formed together with a mass of simple assemblers. You use it together with a programming nanolathe for field construction, after mixing it with a suitable solvent, usually water, to form a nanopaste. But that’s not what we’re talking about here.)

Nanoslurry itself is a complex suspension of materials useful in nanoconstruction, designed to make it as easy and efficient as possible for nanofacs to pick out the bits they need. It comes in a variety of different kinds and grades, most of which are intended for one specialized industrial application or another. Standard-grade, which is what is shipped out as a public utility down municipal nanopipe systems, comes in two forms, informally referred to as “gray” and “green”.

The nanopipe you have plugged into your domestic cornucopia, for that matter, is actually a four-pipe system. The first supplies gray nanoslurry – which is water, long-chain alcohols, sulphur and nitrogen compounds, a suspension of iron and copper oxides, heavy metals, silicates, acetats, nanograins of industrial plastics, ceramics, and alloys, and prefabricated molecular components, or to put it another way, everything you might need to perform “common mechanosynthetic applications”. The second supplies green nanoslurry, which is specialized towards organic synthesis applications – what this means, of course, varies from world to world. And the third is the special-order pipe, which gets aliquots of specialized feedstock shot down it upon request, because while you may occasionally need, say, 2.1 g of technetium, it’s something specialized enough that there’s no point in including it in the regular feedstock.

(The fourth is the return pipe, that pumps what’s left after the nanofac has picked out what it needs back to the nanosource for recycling.)

And what the nanofacs need is, well, exactly what elements are in the finished product. (Plus a certain degree of in-process waste that ends up squirted down the outgoing pipe back to the nanosource.)

So, so far, we’ve just pushed the problem back to the nanosource; after all, nanoslurry doesn’t exist in nature, so it has to be manufactured. Which is what nanosources do: out of a variety of sources. Air mining, for worlds with atmospheres that have useful components. The bactries of chemical companies, refining volatile asteroid-liquor into useful chemicals with bacterial aid. Giant metal ingots shipped from smelters, which are reduced to slurry components. Reclaimed and purified chemicals from recycling plants and biocleaning cascades. In short, from the ends of all the conventional supply chains. Larger autofacs, like the Hive, will usually have their own nanosource(s) to produce all the specialized feedstocks that they want, especially since autofacs use a bunch of those raw materials elsewhere in their non-nanotech manufacturing processes.

So now we’ve just pushed the question back another level, haven’t we, to “can the people the nanosources use as suppliers synthesize elements?”

To which the answer is, finally: yes, but they usually don’t.

Nucleosynthesis is possible. There’s an entire engineering discipline, alchemics, that specializes in this sort of thing. But it’s neither cheap nor convenient, inasmuch as it still involves banging nucleons together and trying to get the wee buggers to stick, a process that tends to involve particle accelerators and nucleonic furnaces and isotopic separators and mucking about at absurdly high energy densities and low efficiencies. That said, it is now regular non-experimental engineering, and a large enough autofac might well include the equipment.

…but economically, it is almost always cheaper to dig the stuff up and have it shipped to you for nanosource processing than try to manufacture it on site from other elements. Nature’s production process may be slow and uncomfortably explosive for anyone within a couple of hundred light-years, but, damn, does it have economies of scale.

This effect is only amplified, of course, by the fact that alchemics equipment is also what you use to produce gluonic string,  muon metals, and various other kinds of exotic matter that genuinely don’t occur in nature anywhere. Now that’s what you call comparative advantage!