Every so often I read where someone says we could mine helium-3 from the moon. What I don’t understand is why this is considered a likely or worthwhile prospect. The problems I see are [ul]
[li]There is no such thing currently as a working fusion reactor- not even a barely-breaks-even laboratory model, let alone a prototype of an industrial power generator. It seems simply taken for granted that one will arrive eventually. But physicists have spent decades simply shaving some zeros off the order of magnitude by which they fall short of sefl-sustaining fusion. This has led some wags to proclaim that “fusion is the energy source of the future - and always will be”.[/li][li]The point of using helium-3 instead of tritium is that it would be clean(er). But any plasma hot enough to fuse deuterium and helium-3 would produce some tritium anyway by D-D reaction. So would it be worth it?[/li]Would it really be cheaper to obtain helium-3 from the lunar regolith than to simply breed it from tritium as we do now? You’re talking about establishing a gigantic industrial infrastructure on the moon, and we’re still paying ten thousand dollars a pound to put satellites in low earth orbit. [/ul]
I’ve read that some of the big fusion reactors have actually reached the break even point now, but haven’t gotten beyond it.
The reason for going to the Moon to mine the Helium3 that’s there is that it doesn’t have to be processed out of anything, it’s pretty much laying about in it’s pure state, so we could skip the whole business of having to process it out.
Also, it really doesn’t have to be handled by a massive industrial complex. Automated machinery can do much of the work, and getting it to Earth, would be cheaper than getting things up from Earth to the Moon. A nuclear/solar powered rail gun could fire projectiles at the Earth for pennies a shot. The projectiles would need only occassional thrusts from small thrusters (which could be fueled from oxygen extracted from lunar material).
Additionally, there’s literally tons of the stuff readily available on the Moon, whereas the processes we have on Earth produce significantly smaller amounts at a time. Just a few tons of the stuff would be enough to satisfy the US’s electrical needs for a year.
So, no matter how we pull it off, the payoff will be huge.
[General Turgidson] Mr. President, we cannot allow a Helium-3 gap! [/General Turgidson]
Yes - but will it be huge enough? Extracting enough He3 to be worthwhile will mean processing staggering amounts of lunar ore - you have to process 200 million tons of ore to get one ton of He3. To power the entire USA at our current energy requirements would take 25 tons of helium annually, which translates to 4 billion tons of lunar ore that need to be collected, ground, processed, and then dumped elsewhere. For comparison, giant bucket wheel excavators weighing about 1000 tons can scoop about 80 million tons of ore in a year, assuming you run it 24 hours a day nonstop. So, assuming similar technology to process ore on the moon, you’d need to land over 60,000 tons of equipment on the moon just to scoop up the ore. The Apollo lunar lander, for comparison, weighed about 17 tons - and that included the descent engines, fuel tanks, and guidance systems that need to be added in addition to the payload weight of the ore-scooper itself. And that needed a Saturn 5 to get it there. So that’s over 3500 saturn 5 rocket equivalents just for the ore gatherers. Then there’s the ovens to extract the He3, the machines to carry the ore away to dump piles, the launcher to get the He3 back to the Earth, the nuclear or solar power stations to provide power to the whole operation…
Maybe you could do this with unmanned machinery, but it would require a lot of unmanned machinery. We’d need to build a space infrastructure several orders of magnitude more capable than anything we’ve built in the past, and almost certainly have to send up regular ships to replace supplies and broken equipment. With the magnitude of equipment needed, sending along a few humans to oversee the operation is trivial by comparison.
On the other hand, deterium and tritium fusion is a lot easier to achieve than He3 fusion. We have already achieved break-even D-T fusion in test reactors. It just hasn’t been made into a commercially viable fusion reactor yet. The only drawback to it is that the reactor walls become radioactive after time. So the issue comes down to the cost of building a truly massive space program versus the costs of dealing with some radioactive waste - which we can do now.
Now, I’d love to see a truly massive space program built. But He3 mining alone is not much of a justification for it.
By “pull it off” I meant fusion by any means (excepting nuclear weapons, of course), be it from mining lunar sources or doing it here on Earth.
Comparing the technology needed to the Apollo set up is wrong. Not simply because the objectives of the Apollo landings are different, but because the materials we have available to us today are vastly superior to those available in the 1960s. Composites are lighter and stronger than the alloys the engineers had to work with back then. Additionally, rocket design is better, so we’re able to get more fuel efficiency out of a rocket today because we understand better how to mix the fuels than they did in the 1960s. Also, you’re thinking in Earthbound ways, and not Lunarbound ways. A 100 ton ore carrier on Earth is going to be able to haul 600 tons of ore on the Moon (gravity being 1/6th that of Earth). Lunar based ovens would also be a lot simplier than Earthly ones. There’s ample sunlight hitting the Moon for one to use focused mirrors to heat the ore up, no need for fancy electronic furnaces.
As for dealing with radioactive waste, sure, there’s lots of ways we can dispose of it, but if you talk to the people of Nevada, they’re not real happy with the favored method of the moment for doing it.
It’s not as great a difference as you might think. Yes, we can make alloys and composite materials today that are stronger than those used used in the 1960’s, but it’s a matter of a few percentage points when it comes down to the final rocket performance. There has been no breakthrough in materials which would change the fact that you’d still need thousands of Saturn-5 equivalent rockets to pull off a worthwhile lunar mining program. The only place where modern rockets are significantly more efficient today is in the electronics - we can make computers much smaller, lighter, and more reliable than those used then. But even back then the computer was only a tiny fraction of the rocket’s weight.
Yes, but again, it’s a matter of incremental improvements. The liquid-hydrogen burning engines in the space shuttle have a vacume ISP (that is, how much thrust is produced per fuel burned) about 10% better than the J-2 engines used on the Saturn 5. Most of the improvement has been in reliability and reuseability.
On the other hand, lunar equipment has to be designed to deal with conditions a lot harsher than those on Earth. 2 weeks of raw unfiltered sunlight, then 2 weeks of utter darkness, and the violent temperature swings that causes. Thermal control under those conditions is a very serious issue - you can’t keep your equipment cool by blowing outside air over it, so any serious mining machine is going to need large radiatiors and liquid cooling loops, which need to be kept from freezing solid during the lunar night. One of the soviet unmanned lunar rovers died after dust got on the radiator, ruining its thermal emissivity and overheating it. Speaking of lunar dust, it’s apparantly incredibly abrasive - no wind or water to wear all those jagged edges down into nice smooth dust grains. This was also a serious problem for the Apollo missions - after just a few days on the moon, the suits were wearing badly at all the joints. Power is also an issue - you can use solar power, but a serious mining operation needs a lot of power, so that means fairly large solar arrays, and it limits your operations to the daytime. Or you can send up a lot of nuclear plants, but they’re not exactly lightweight.
And even if you assume that mining equipment on the moon can handle 6 times as much ore as earthly equipment, that’s still over 10,000 tons of payload needing to be delivered to the lunar surface just for the ore extractors.
Which limits your oven’s duty cycle to 50% at best. And how many ovens (and associated hardware) do you need to handle a throughput of 5 billion tons of ore a year?
No matter what, you’re looking at a massive industrial operation here. Improved materials, rockets, and other technology will help you some. But you’re still talking about a space launch infrastructure many orders of magnitude larger than anything we’ve ever had. Not that that’s a bad thing, but I suspect if we ever get to the point of being able to build the launch systems required, we may have better options for getting energy anyway. There’s always the possibility of hydrogen-boron fusion. It’s much harder than even he3 fusion, but also produces no neutrons, and uses fuel quite common on Earth.
It might actually be easier to just build D-T fusion plants, then build rockets to boost the resulting radioactive waste out of the solar system. I suspect you’d need a significantly smaller launch infrastructure to do that than to set up a He3 mining operation on the moon.
Oh sure, but then you have to worry about how the aliens will respond by getting nuclear waste dumped on them. I can see it now. The population of Earth rejoices at getting rid of a huge amount of deadly waste, only to be killed by pissed off aliens.
But you wouldn’t believe how those few percentage points quickly add up. The designers of the LEMs managed to take the first model, which was too heavy to land (thus used for a test on Apollo 9), to the model used on Apollo 17 which enabled the astronauts to spend a couple of days on the lunar surface. Before the program got killed, NASA had figured out how to tweak the hardware they were using on the Apollo missions to extend stays to a month or more.
Again, even a few ounces of improvement can have a big payoff.
We do have plenty of experience building things to run around on the Moon, and we’ve got even more experience building heavy earth moving equipment, so it’s not like this is a total impossibility. The Martian rovers (admittedly benefitting from a much milder climate) have exceeded their design life by a number of months now, and are still running.
My understanding of it (and I may be wrong in this) is that the ore is fairly easy to get to, so it’s not like we’d have to tunnel through several hundred feet of lunar surface to get to the He3, it’s all lying about on the surface.
Yeah, but that 50% is 24/7 182.5 days a year. As for how many you’d need, I’ve no idea. If you know how hot the lunar ore’s got to be in order to break the He3 free, then this site should be able to tell you the size and number of oven’s you’ll need. (Earth based data, so a lunar based one would operate at slightly greater efficiency since the sun’s not blocked by clouds on the Moon.)
Eventually, it’d need to be a massive set up, but even if the breakthroughs needed on the fusion front were to occur today, it’d still be at least 10 years before the first plant was up and operational (since so many people hear the word “nuclear” and immediately think “evil” it’s going to be hard to find a place to site a plant). So it’s not like we’d need a operation capable of providing the necessary tons of fuel running all at once. I’m sure, also that we wouldn’t build one enormous power plant to supply the entire US, but lots and lots of small plants scattered across the US, so timing it correctly wouldn’t be that difficult. And I don’t have time to dig up a cite, but NASA has designed and tested a laser powered space craft (i.e. a giant Earth based laser fires upwards and ionizes air, to lift a ship into space), so that eliminates much of the rocket needs, plus, part of the cost could be absorbed by SDI (since they’d probably like to get their mitts on a really high powered laser).
Considering the way the nutters go crazy whenever NASA tries to launch a probe with a few microounces of plutonium or whatever, I can’t imagine that idea going over too well. . . .
And in this thread loopydude mentions something which would make a good reason for siting it all on the Moon.
For it to happen, it’s not going to be with traditional manufacturing techniques.
But if we could come up with something like a nanotech replicating factory that used lunar materials to manufacture its own harvesting robots, you might have something.
But that’s just science fiction at this point.
Well also: there may only be 25 pounds of tritium in the world.
[sup]3[/sup]He + [sup]3[/sup]He -> 2P + [sup]4[/sup]He
The significance is no neutrons. Rather than needing huge magnetic fields, simpler electric fields can contain stuff. (at least that is my understanding)
D + [sup]3[/sup]He -> p + [sup]4[/sup]He does create some T but MUCH less than DD.
http://fti.neep.wisc.edu/neep533/SPRING2004/lecture26.pdf
Whole course on lunar He:
http://fti.neep.wisc.edu/neep533/SPRING2004/neep533.html
Brian
I don’t have the article handy but in either Wired or Discover some years ago was an article about a couple of professors at a university in the Western US, who were devising a scheme to use robots about the size of the Mars rovers to build a sun farm in the US desert. Apparently, the big stumbling block (besides getting the money to do this) was writing the software. They weren’t going to be using anything that wasn’t based on off-the-shelf technology, other than the software as I recall.