Hi, everybody. I’m a newbie here, although I’ve been following FF’s progress for two or three years. I certainly have high hopes that p-B11 fusion will succeed—it seems like a much more desirable neighbor than any other form of energy production. (Including solar, when you start talking about paving over whole states with solar panels!)

I’m moved to post for the first time by just having read another apologia for mining He-3 on the moon—I won’t link to it, since I’m sure you’ve all read many such already. Now I’m a big advocate of space exploration, and any excuse to interest the powers-that-be in developing more economical launch vehicles in particular should be encouraged, since everything else follows from that.

However…doesn’t this seem nonsensical to anybody but me? If you have achieved temperatures that can fuse He-3-D, can’t you fuse deuterium with itself? (And how do you keep it from doing that even in the presence of He-3? But that’s another discussion.) If you can do that, wouldn’t it be infinitely cheaper to put D-D reactors in space and make your own He-3? (Especially since vacuum isn’t at a premium in space and the vacuum vessel is a big part of the weight and cost of any fusion reactor?) Every pound of deuterium is going to produce six ounces of He-3 and six ounces of tritium that will decay into He-3. How much mining and refining equipment are you going to have to land on the moon to scrape 12 ounces out of the regolith?

You could undoubtedly extract enough power from the proton and neutron (they carry 3/4 of the energy after all) to run the operation, with some left over. Periodically deorbit a small container of pure He-3 and sell it for an astronomical sum. It would still be much cheaper than squeezing the moon for it.

Heck, use the neutron to produce on-site power and let the proton escape aftward and you have a very low-thrust, high specific-impulse space drive. Go back and forth to Mars a few times, producing very expensive reactor fuel all the way. Each trip would take years and probably take √2 times the Hohmann ∆V, but remember you’re trying to use up fuel, and there wouldn’t be any problem paying for it.

That said, I’m really pulling for p-B fusion, and wondering how many megawatt-years I poured down the drain washing my hands with Boraxo after working on my car all these years. Now’s the time to tear my theory apart—I look forward to your reactions.

The moon is unfortunately rather barren of easily extractable resources. Its advantage, for mining operations, is that it is fairly nearby. But it has almost no hydrogen, which is desperately needed as a resource for materials extraction. I would find asteroid mining to be more worthwhile, probably.. if-only we could park one into earth orbit.

What Focus Fusion is attempting, is aneutronic fusion. No neutrons means no long-lived radioactive waste, and no bomb-making.

And therefore there is no plan to breed tritium, and no good reason to want to, if you can just burn boron.

vansig - 30 January 2011 04:13 AM

And therefore there is no plan to breed tritium, and no good reason to want to, if you can just burn boron.

That was my point. D-D produces helium-3 and tritium, which you allow to decay to He-3 before shipping it dirtside for use in (aneutronic) power reactors.

EDIT: I should perhaps make this even clearer: this scenario is predicated only on the eventuality that p-B11 doesn’t work, nobody wants to burn D-D or D-T on earth because of the neutrons they produce, and we’re reduced to trying to obtain helium-3 somewhere for D+He-3. (Why not He-3+He-3? No side reactions there.) I just think it would be enormously cheaper to produce our own with D-D reactors in space than ship mining and extraction equipment to the moon.

vansig - 30 January 2011 04:13 AM

What Focus Fusion is attempting, is aneutronic fusion.

D+3He itself is an aneutronic reaction too.
Hypothetical fusion reactor using this mix would actually produce some neutron flux due to D+D side reactions.
However this flux should be several orders of magnitude lower than D+T, if the reactor keeps the fusion temperature optimal for the best D+3He reaction rate

to topic starter: as for mining Moon for 3He - hmmm, I think it would be worth to return to this idea in… say 20-30 years.
when we have at least working D-T fusion.
or may be never return to it if we have working p-B11

Mining the moon makes no sense to me, although governments have eco-political needs to fund enormous projects which produce impressive images showing how hard it is to do anything (that wasn’t designed to be the most elegant solution to the publicly stated problem).

As for mining asteroids, I’d go to them rather than try to figure out the laws of unintended circumstances regarding moving new and significant masses into earth orbit. Besides, that kind of mobility will open up the space travel and vacation industries. Been waiting for that all my life.

Aeronaut - 30 January 2011 08:12 PM

Besides, that kind of mobility will open up the space travel and vacation industries. Been waiting for that all my life.

First, belated congratulations on your 1000th post. Yeah, I’ve been waiting for that my whole life too. I was 17 (well, almost) when we landed on the moon for the first time. Now I’m 58, and we’re farther from being able to land on the moon than we were in 1961. Our only sign of movement is SpaceX reinventing the wheel and taking us back to 1960—and that’s considered progress!

I did a little ballpark arithmetic on my plan—if you had a 1000-tonne spacecraft powered with a D-D reactor, only using the proton for thrust, you’d need about 16 tonnes of deuterium to transport several hundred tonnes of payload from low earth orbit to low mars orbit and back, and in the process produce about 12 tonnes of helium-3 (well, 6—you’d have to wait for the 6 tonnes of tritium to decay). That should be enough to produce (with some added deuterium) about 200 GW-years of electricity. That’s got to be worth something on the open market.

As always, getting rid of waste heat is the real problem. If you took two years for each leg of powered flight, you’d need at least 40 acres of radiators, and there goes your payload. Maybe you could take longer—I’m assuming this is cargo-only, people would have to go much faster because of the cosmic ray exposure. It would be one way of making space travel pay for itself. You’d need to build essentially this interplanetary spacecraft even if you were parking it in orbit to burn deuterium into helium-3. You’d have to use some of that thrust for stationkeeping. Why not go somewhere with it?

Thanx for noticing, Arvid. I’m 53, and if I wait for the existing organizations to provide the vehicles, I’ll never get into space. I’m looking for the space elevator, myself.