One night, as I was putting my daughter to bed and waiting for her to fall asleep, I tried to think of some new markets for space utilization.

We often hear about attempts to find industrial uses for microgravity for growing crystals, for purification of electronic materials (which is an actual thing with ACME Advanced Materials: http://www.a2-m.com/ ), maybe growth of certain metal foams, etc. However, in space, you’re in both a hard vacuum and not physically resting on anything, so you can spin up something, and it will simply keep on spinning (stably, if you spin it around the correct axis) nearly indefinitely without any additional energy input and no wear on bearings or anything. So in fact, you can get basically any gravity level you want, including HYPERgravity, nearly for free.

What are the applications of this?

The most obvious one I can think of that has the biggest market potential is isotopic enrichment of Uranium-235 for nuclear fission fuel. The world demand for electricity is about 10^20 Joules electric, and the price of Uranium fuel is about half a cent per kWh. About 40% of that is the cost of separation, with a Separative Work Unit costing around $100. So enrichment cost about 5*10^-10 dollars per Joule of electricity. That gives a world market for up to $50 billion for separation if we used just nuclear. If 10% of our market is nuclear, then $5 billion. Given 10^14J/kg of fissionable fuel and cost of 5*10^-10 $/J, then you have $50,000/kg of Uranium. Knock that down to 20% due to thermal to electrical conversion (power plants are usually better than that), and we’re at $10,000/kg. If you can get launch costs down to $50/kg, then it might be worth doing this (because you’re launching natural isotope ratios of Uranium to make the math easier). But interestingly, near-pure U235 is something that probably WOULD be economically worthwhile to export from Mars or Moon or asteroids (processed in orbit).

One can imagine other uses for isotopic separation, like lithium-6-enriched metal alloys. Lithium 6 is about 15% lighter than natural lithium. The best conductivity-to-mass-ratio wires (other than superconducting or microscopic graphene or nanotubes, etc) at room temperature is Lithium-6, nearly 4 times as good as copper. But that’s a much smaller market.

EDIT: I want to add some more realistic figures for cost, etc. There is currently perceived to be a glut of separation capacity, so the SWU price is still just $82 or so. But there’s also kind of a near-monopoly (quadropoly or something?) among separation providers, and the US is still using crappy gaseous diffusion plants which are super inefficient. So there may be a good argument for doing it anyway as a form of avoiding a sort of cartel arrangement. Also, since natural uranium is so poor in U235, it may actually make sense to pre-enrich the uranium before launch so that you don’t have to launch as much of it. Suppose we’re trying to make 95% U235-enriched Uranium (quite highly enriched) and want our “tails” to contain just 0.1% U235 (vs 0.7% naturally). We want to maximize the number of SWUs we do for a given launched mass. I’ve found that occurs at about 25%-U235 pre-enriched. 5.23 SWUs per kilogram of uranium. According to this calculator: http://www.wise-uranium.org/nfcue.html

(I could have used the full expression for SWUs and massaged it with calculus to give the actual maximum, but I’m getting lazy.)

Multiplying that by the cost per SWU (about $82), we get about $430 per kilogram. In other words, the market value of the work we can do separating that Uranium, if our orbital isotope enrichment goes well,

is about $430/kg. So we probably need launch prices to be down around $100-200/kg for this to really work. But that’s not unreasonable, and there’s also some value in having an independent capability to do this.

….Then again, the elephant in the room here is that we’re talking about launching tons of already-highly-enriched uranium (enough to make a crude fission bomb) and recovering VERY highly enriched uranium. Enriched so much that we’d better be careful about how much we have together at one time. Kind of goes without saying that there’d be political opposition to such a scheme! But still, it would be another space market.

(And I redid the numbers for more power-plant-grade 4.5% low enriched uranium given natural 0.711% feed and 0.1% tail… It’s about $119-worth-of-work/kg launched, so not actually as bad as I thought, and isn’t super highly enriched and so politically is more feasible, since you’re not just shipping bomb-grade material around.)

…and all this is pretty irrelevant if you start breeding your fuel from natural uranium and thorium, which probably makes sense in the long term.