good grief..... lunar helium-3 again

10kBq Jaro · Senior Member

good grief..... lunar helium-3 again

iprimap · Veteran Member

It is easier to produce Helium-3 in the following fashion:

Seed a fission nuclear reactor such as TVA's Watts Bar (http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/tritium.html with Lithium-6. On neutron absorption Lithium-6 will produce Helium-4 and Titium (or Hydrogen-3). Tritium has a 12.32 year half life wherein it undergoes beta-minus decay to Helium-3.

I would have to imagine that both the US and Russia have plenty of Helium-3 left over from all the tritium they have produced for their thermonuclear weapons. Mining helium-3 on the Moon is far more costly than production in fission nuclear reactors as described above.

Regards,

Paul P.

GoogleNaut · Guru

As much as I like the idea of mining the moon, I have to agree that mining the moon for helium-3 makes little sense, because we haven't even demonstrated an economically operational fusion reactor that can burn deuterium and tritium, which is easier to initiate than helium-3 and deuterium.

It's a little like putting the cart before the horse, so to speak....

Now when (or if) we do develop thermonuclear fusion in a big way, and if fusion power systems are available for deep space propulsion, the lunar helium-3 resources may in fact become important.

Infact, given a lengthy enough industrialization period (say 1000 years) with interplanetary and possibly interstellar travel, then the helium-3 resources available in the atmospheres of the Jovian planets might actually become attractive....

-- Edited by GoogleNaut at 20:36, 2005-08-21

John · Senior Member

Several years ago I became very interested in He3 as space fuel for fusion engines. From a space application D-T fusion is very good as 80% for the energy comes off in neutrons which are fairly useless unless you are actually going to breed tritium on your spacecraft. At the time I had the naive hope that you could fuse He3-D at about twice the temperature of D-T well that was wrong its more like 10 times the temperature. Very close to the temperature of D-D fusion. So guess what? You have a lot of D-D fusions as well as the He3-D reactions. Still a lot of neutrons.

So if you are going to operate in that temperature why not just use what is called Cat D-D. You do the D-D reactions to get D + D --> T + H and D + D --> He3 + n. Then you immediately get a D + T --> He4 + n and almost as fast (at those temps)

He3 + D --> He4 + H. 60% of the energy is in charged particles that are good for propulsion and best of all the fuel is very available on Earth not radioactive.

Oh, it is true that decaying tritium from the nuclear arsenals is a source of He3 but the quantities are far too small for space propulsion or as a major energy source here on Earth.

It seems clear to me that it is just a political decision that prevents us from having first generation, i.e. D-T fusion for energy on for electrical production. Given our current state of knowledge a focused national commitment program like Apollo could have working reactor with a decade.

-- Edited by John at 14:58, 2006-01-29

GoogleNaut · Guru

Until we demonstrate an operable thermonuclear reactor, I think it's hard to justify developing a lunar Helium-3 extraction fascility as the primary reason to go there...

However, I would add that if we go back to the moon anyway, and if we develop insitu resource utilization with extraction of useful materials such as titanium, aluminum and other materials from lunar regoltih, a byproduct of this materials processing will naturally be volatiles anyway. So then it makes sense to store any extracted helium-3 we find, along with nitrogen, hydrogen, and carbon--volitiles on the moon will be a gold mine for lunar operations anyway--savvy lunar miners would hedge their bets and store the helium-3 anyway just incase fusion reactors able to burn it do come online.

But to go there with the intended purpose of only extracting helium-3 is foolish and shortsighted without an operating thermonuclear fusion powerplant infrastructure to consume it...

Presently, helium-3 is not the holy grail of fusion. Not when Tritium and Deuterium have a lower ignition temperature--neutrons or not. And we haven't been able to demonstrate a working fusion reactor based on those fuels yet either so it seems premature to go looking for helium-3.

Andrew · Senior Member

I thought THE ultimate holy grail of divinity for fusion is p-B11 reaction?

GoogleNaut · Guru

Well, if it works, then it'll be the holy 'grail'.

Deuterium and Tritium have the lowest ignition temperature of the fuseable isotopes--and they produce the most energy per nucleon.

This is why this combination is used 'exclusively' in thermonuclear explosives.

However, if p-b11 works well enough--and I am very skeptical at this point--then there will be plenty of fuel materials all around the solar system--ideal for future propulsion and power systems.

Andrew · Senior Member

By the way, what about Lithium-6? It's cross section is larger then Helium-3's but lower then Boron 11's, while still plentiful on Earth.

John · Senior Member

Well Lithium-6 is the source of the tritium. Li6 + n --> He-4 + T is how you make tritium (at least that is the main method). This can occur in a nuclear reactor to breed tritium or in the "secondary" of a nuclear bomb. The neutron flux from the primary which is basically a fission bomb or ofter a boosted fission bomb flows through the secondary which is filled with Li6D breeding tritium based on the above reaction. Then the T + D --> He4 + n reaction generate more energy and more T. Yes, Li6 is very involved.

First generation fusion reactors primarily will be fueled with Lithium. The are basically tritium breeders. You have to start of with tritium made in a fisson reactor to start the process. But, then you react D + T to make He4 and neutrons. 80 percent of the energy comes off in neutrons which then interact with Lithium both to breed more tritium and absorb the neutron energy to convert it to thermal engergy.

And has been stated D-T fusion happens at temperature much lower than other fusion reactions.

GoogleNaut · Guru

I agree with John.

DT fusion will be much easier also because these heavy isotopes of hydrogen are intrinsicly 'less lossy' than higher Z materials like boron.

I don't see any real reason to go to the moon for Helium-3 when Lithium-6 can breed an isotope which is easier to fuse. Besides if you don't like Tritium, then let it decay to Helium-3. It 12.3 years, half the stuff will turn into Helium-3, and that source of He3 will be much easier to get here than the moon.

Of course, it's all mute if we don't even have a working DT reactor yet, let alone one that burns He3!

-- Edited by GoogleNaut at 05:01, 2007-04-17

Andrew · Senior Member

Yes, but I recall that using tritium as a Helium-3 source is not very optimal. I'm just thinking what other possibilities there are. Perhaps 3rd generation fusion will use Li6?

John · Senior Member

Actually B-11 + p --> 3 He-4 is easier to achieve than the lithium reaction. That's probably the third generation. The reason the space people got into
He-3 was that He-3 + D --> He-4 + p which give all of the reaction products as charged particles. So you get the most useful thrust out of a fusion rocket with that reaction. Also no neutrons solves a lot of problems. The problem is that the He-3D reaction occurs at so hot a temperature that you also get a lot D-D reactions about half of which produce neutrons so your aneutronic reactions is gone. Hey but its a good excuse to go to the moon!

Andrew · Senior Member

No, a good excuse to go to the moon is making it a staging area for future space explorations as well as an important place to do actual scientific research.

GoogleNaut · Guru

To support that level infrastructure will require a lot of volatiles. Either from the poles (hopefully) or from comets (a lot more expensive,) but volatiles will be needed for everything from rubber seals, propellants, chemical energy storage media, or even as simple water to grow crops and recycle air. To establish an initial base is one thing--to establish a colonization effort, that's a completely different animal. And that makes sense only if the volatile supply problem is solved.

Andrew · Senior Member

Where there no explorations whether there are violatiles at the poles? Even just by robots? Something akin to the Mars Roover might be helpful.

GoogleNaut · Guru

I believe a lunar robotic polar mission, something very much akin to the RTG powered Mars Science Laboratory slated for launch about 2009-2011, is actually being planned for extended lunar polar exploration. If there is a few billion tons of water ice locked up at the poles, we need to know if it't there, and how much!

Andrew · Senior Member

Weren't there in the past? One would think that the Moon is easier target then Mars.

EDIT:

Actually B-11 + p --> 3 He-4 is easier to achieve than the lithium reaction.

Wha? My source here: http://fusedweb.pppl.gov/ says that p-b11 reactions is harder then p-li6 reaction (albeit, it gives more energy).

Can you please link me to a more detailed table about fusion reactions? Most I come across aren't very detailed.

-- Edited by Andrew at 13:23, 2007-04-21

John · Senior Member

My source is the book Fusion Energy in Space Propulsion Ed. by Terry Kammash. There is a graph on ch 4 page 100 Fig. 2 A comparison of D-T and advance fuel reactivities. It shows reactivity vs. T in KeV (per particle). It shows the p-B11 peaking before the p-Li6 about 400-500 KeV vs more than 2000KeV respectively. Interesting the curves cross below 50 KeV so for reactors running below optimium temperature the p-Li6 is a little more reactive. Given the energy output differences why not go for the p-Be11?

GoogleNaut · Guru

...but a DT reaction will be much lower than that, and the neutron flux will, when interacting with Lithium-6 and 7 in a blanket surrounding the reaction chamber, breed more Tritium, and recover another 4-6 MeV per neutron interaction as well. DT fusion, despite all the misgivings about neutrons, I think is still just about the most practical way to fuse hydrogen out there...

-- Edited by GoogleNaut at 00:28, 2007-04-23

10kBq Jaro · Senior Member

GoogleNaut wrote:
DT fusion, despite all the misgivings about neutrons, I think is still just about the most practical way to fuse hydrogen out there...

And speaking of practical, the most practical/ economical way of doing DT or DD fusion is using contained thermonuclear explosives -- as in the PACER project : http://en.wikipedia.org/wiki/PACER

But as the article says, "the political effects of beginning a large-scale production of nuclear bombs could potentially be large, and with increasing bomb numbers, increased security measures would be necessary.
The entire system - fissile material production, bomb fabrication, and power generation - could be carried out in a single well-guarded site."

PS. I cut off the quotation, because the rest of it is balloney, designed to discourage any thought of ever implementing such a scheme, and to encourage spending endless billions on the Tokamak white elephant, that will not be economically practical -- at least until ambient-temperature superconductors are invented.
The slant of the article is not surprizing, as it references a paper by Richard Garwin, a perennial anti-bomb activist -- regardless of whether its for weapons or for "swords to ploughshares" applications, including such things as the Orion nuclear pulse-engine.

By contrast, PACER would have been "practical" decades ago -- much like Orion.

-- Edited by 10kBq Jaro at 01:20, 2007-04-23

Andrew · Senior Member

The charm I find in aneutronic reactions is, that according to site I linked, about 95% of the energy could be directly harnessed by magnetohydrodynamic methods from aneutronic reactions.
While only 50% would be achievable with neutron reactions which we get their energy from the neutrons heating water that produces steam, that spins the turbine, that spins the generator.

DT is easiest to do, but I think that's its only charm (I'm saying this as an amateur).
Tritium can only be gained artificially (yes, I understand that tritium can be gained from fusion process) and is mildly radioactive.
Deuterium can be gained from seawater (I'm not sure, but I think I can buy heavy water at the right shop, from there I only have to electrolysis it to get deuterium), and Helium-3 can be gained from the solar wind itself. Lithium-6 and Boron-11 are fairly light elements abundant of Earth, and would be further available with the fusion rocket technology such would unlock.
There is also the issue that maintenance is easier: you don't have to replace reactor elements regularly and you don't have to worry about radiation (much).

I have no doubt that first generation fusion reactors will use D-T reactions as target, but as fusion technology is perfected, advanced fuels will be regarded superior unless the aim is to get allot of neutrons. And we have fission for that, don't we?

John · Senior Member

I was a big fan of He3-D for fusion space systems but the problem is the lack of a good supply of He3. Another reaction that may be considered (but not first generation) is Cat D-D. You run a reaction of D-D at Q<1. But hot and dense enough that the T and He3 produced by these reactions fuse immediately. It also has to be hot and dense enough that you get the amount of T and He3 that you need so that the whole process is a net energy producer. The D + D --> T + p (50%) and He3 + n (50%). The He3 + D --> He4 + p and T + D --> He4 + n would follow immeadiately and produce most of the energy. About 60% of the energy is in the form of charged particles. The fuel is cheap and available.

Andrew · Senior Member

Interesting. Very interesting.

I thought of this, also I didn't expect that 60% of the energy is charged particles (I sadly have no proper education in quantum mechanics, but I'd love to have, can you suggest on-line sources perhaps?).

This has its charm. Lower amount of neutrons can still give tritium (or possibly other useful isotopes?) but are less of a hazard, while energy gain from the reaction is much purer (due to it gained in the form of charged particles, although I suspect that the "ion catchers" will have to be replaced regularly).
Another charm of this is that deuterium can be widely gained.

Personally I suspect that He3 will pretty much fuel the space industry, as its only there where it can gained. As space and the need for He3 grows, perhaps even the gas giants will be mined.

GoogleNaut · Guru

Yes, but the trouble is to create a self sustaining reaction requires temperatures approaching 1 billion K. We haven't yet achieved break even, let alone engineering break even, let alone economic break even with the easiest of these reactions: the DT fusion reaction. Only thermonuclear weapons have ever achieved substantial yields of energy from fusion on Earth. And only thermonuclear detonations as yet can achieve Q>>1--but they are not even considered a viable energy source because of the political situation involving restarting nuclear explosive production; the risks inherent in contamination with bomb residues; and that doesn't even address the environmental risks associated with the seismic stresses involved in multiple detonations over long periods of time.

As much as I love the idea of thermonuclear fusion, it is extremely difficult. He-3 supply isn't really the problem--it's overcoming Coulomb repulsion of nucleii. Temperature and pressure can achieve this, with difficulty.

Interestingly enough, nuclear weapons designers do not view He-3 as a fuel, they view it as a contaminant, or worse, a poison. One of the problems with keeping a nuclear weapons stockpile, is constantly reprocessing the tritium boosters to remove the He-3 contaminants. The He-3 can actually soak up neutrons and can slow or even stop a chain reaction cold: a weapon can actually fizzle if it has too much He-3 in the booster capsule.

This just indicates to me that He-3+D fusion is a lot harder than is generally advertised. If it was that easy, then why don't weapons designers exploit it?

Food for thought!
Ty Moore

-- Edited by GoogleNaut at 19:54, 2007-04-24

John · Senior Member

A few points about my Cat D-D comments:

I said that it definately was NOT first generation.

It's also easier to achieve than B11-p.

The context was fusion space propulsion.

If we had a working He3-D power fusion space engine we would have some trouble getting enough He3 to power it assuming routine use. Compare that to a pure deutrium fuel. It is somewhat more challenging but quite a bit of payoff. This is not a near term issue of course.

An interesting point about He3 as it does have rather high neutron cross section. I bet the reprocessing of bomb tritium is one of our larger source of He3. But, also consider that the first hydrogen bomb, i.e. the Mike devices was largely a tank of liquid deuterium for the secondary. The lithium-deuteride devices came shortly there after as a cryrogenic bomb was not very practical.

-- Edited by John at 01:58, 2007-04-25

GoogleNaut · Guru

O.K., yeah once interplanetary commerce with fusion drive vessels commence, then we're going to need a lot of He-3 provided we go that way. The two biggest sources of He-3 will be Jupiter and Saturn. If we have mastered fusion power systems by then, then it seems like a no brainer to place fusion powered 'scoop ships' into the atmospheres of these planets.

Processing hydrogen and helium gas on the fly, propelled with some kind of fusion powered ramjet engine, a kilometer long 'scoop' ship ought to process millions of tons hydrogen and helium in short order. There is literally hundreds of trillions of tons of the stuff (He-3) in atmosphere of Jupiter so even if we end up using thousands of tons per year, even hundreds of thousands, we won't run out any time soon.

Andrew · Senior Member

Actually Uranus has a smaller gravity well yet still offers a good deal of Helium-3. Jupiter would be a bad choice due to its large radiation and gravity.
Saturn on the other hand has less gravity, a ring full of stuff spaceships can use (water, debris, etc) and a radiation zone not much worse then Earth's.

Oh course a good deal of He3 must be used to supply the colonies and ships there, as solar panels are dead weight by those distances.

John · Senior Member

Ok, there is a lot of helium of the gas giants. But the problem with helium-3 on Earth is also so very rare as a percentage of natural helium that one has to go to expesive proceedures to separate it out. Does helium-3 exist in that much greater percentage of total on the gas giants?

GoogleNaut · Guru

Well doing a google search for "Helium-3 in the Atmosphere of Jupiter" returned a abstract from a scientific paper at:

http://www.springerlink.com/content/v6013031p56l1634/

According to the abstract the deuterium to hydrogen ratio, as measured by the Galileo space craft is:

D/H = 2.6+/- 0.7 * 10^-5

and the He3/He4 = 1.66+/-0.05*10^-4

This suggests that for every million metric tons of hydrogen processed, you're going to get about 26 tons of deuterium. Fore every million metric tons of helium processed, you're going to get about 166 tons of He3. Jupiters upper atomsphere is about 93% hydrogen, 5% helium and the rest are compounds of carbon, sulfur, oxygen, nitrogen, argon, etc.

I'm not saying it would be easy, but this means that there are literally trillions of tons of both in Jupiter's atmosphere. Assuming a technologically advanced mining campaign, it is not too hard to imagine automated fusion powered scoop ships mining the atmosphere of Jupiter, Saturn, or other gas giants for these isotopes and other essential volatiles. A reundezvous with an automated tanker vessel in Low Jupiter Orbit to transfer cargo to a refinery, maybe in orbit about Ganymede, Callisto, or Europa (although these are all within Jupiter's Van Allen radiation belts.) The Isp available from fusion ought to allow something like this without burning up too much of the fuel cargo. I would expect that technologically advanced species may infact do this very thing.

Infact, if one were to create the Terrestrial Planet Finder, if it has the required resolution, it may infact be possible to do spectroscopic analysis of the upper atmospheres of distant gas giants. Identifying gas giants with anomolously low D/He3 concentrations may indicate extensive gas mining and insipient depletion, indicating hundreds of thousands of years, or millions of years of spacefaring civilization.

John · Senior Member

That's a concentration that is a lot high than in helium on Earth. I suppose in the far future we may well use He-3 from the gas giants. However, we will probably be able to develop fusion reactors the will burn He3-D well before that time. My point is that it isn't that much harder to go to the Cat D-D system and the fuel is plentiful on Earth.

Of course how long that will be is a matter of politics as much as science. It think that human technology has reached the point in which some elements of natural techological evolution have broken down. For example we probably could have gotten to the Moon much faster that we did based on history as we know it fixed in 1945. But, we certainly could have been to Mars by now. I think we could at least have a ITAR-type fusion demonstrator running by now. We certainly could have had nuclear thermal propulson by now. We probably could have had some type of second generation shuttle by now. We could have a majority of our electric power produced by nuclear reactors by now. We could have breeder reactors by now.

I could go on with the examples but the point is that space/energy techologies have slowed after the 1970s as a matter choice rather than possibility. So while I can recommend certain courses of action that really could happen they probably won't for sometime. In 1900 a person similar to myself couldn't say that in 20 year we could go to the moon with any basis by comparison.